EE Coaching Notes 3 PDF: Electromagnetics & Electric Circuits

EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS ELECTROMAGNETICS To charge an electroscope by induction, use the sequence: 1. A coulomb is the same as: Answer: 4, 1, 2, 5 Answer: an ampere·second 22. A charged insulator can be discharged by passing 2. A kiloampere·hour is a unit of: it just above a flame. This is because the flame: Answer: charge Answer: contains ions 3. The magnitude of the charge on an electron is 23. A small object has charge Q. Charge q is removed approximately: from it and placed on a second small object. The Answer: 10^−19 C two objects are placed 1 m apart. For the force 4. The total negative charge on the electrons in 1 that each object exerts on the other to be a mol of helium (atomic number 2, molar mass 4) is: maximum. q should be: Answer: 1.9 × 10^5 C Answer: Q/2 5. The total negative charge on the electrons in 1 24. Two small charged objects attract each other with kg of helium (atomic number 2, molar mass 4) is: a force F when separated by a distance d. If the Answer: 4.8 × 10^7 C charge on each object is reduced to one-fourth of 6. A wire carries a steady current of 2 A. The charge its original value and the distance between them that passes a cross section in 2 s is: is reduced to d/2 the force becomes: Answer: 4 C Answer: F/4 7. A wire contains a steady current of 2 A. The 25. Two identical conducting spheres A and B carry number of electrons that pass a cross section in equal charge. They are separated by a distance 2 s is: much larger than their diameters. A third Answer: 2.5 × 10^19 identical conducting sphere C is uncharged. 8. The charge on a glass rod that has been rubbed Sphere C is first touched to A, then to B, and with silk is called positive: finally removed. As a result, the electrostatic Answer: by arbitrary convention force between A and B, which was originally F, 9. To make an uncharged object have a negative charge becomes: we must: Answer: 3F/8 Answer: add some electrons 26. Two particles, X and Y, are 4 m apart. X has a 10. To make an uncharged object have a positive charge of 2Q and Y has a charge of Q. The force charge: of X on Y: Answer: remove some electrons Answer: has the same magnitude as the force of 11. When a hard rubber rod is given a negative charge Y on X by rubbing it with wool: 27. The units of 1/4πε0 are: Answer: negative charges are transferred from Answer: N·m^2/C^2 wool to rod 28. Two particles have charges Q and −Q (equal 12. An electrical insulator is a material: magnitude and opposite sign). For a net force of Answer: through which electrons do not flow zero to be exerted on a third charge it must be easily placed: 13. A conductor is distinguished from an insulator Answer: at none of these places (there is no with the same number of atoms by the number of: place) Answer: nearly free electrons 29. Particles 1, with charge q1, and 2, with charge 14. A neutral metal ball is suspended by a string. A q2, are on the x axis, with particle 1 at x = a positively charged insulating rod is placed near and particle 2 at x = −2a. For the net force on the ball, which is observed to be attracted to a third charged particle, at the origin, to be the rod. This is because: zero, q1 and q2 must be related by q2 =: Answer: there is a rearrangement of the Answer: 4q1 electrons in the ball 30. Two particles A and B have identical charge Q. 15. A positively charged insulating rod is brought For a net force of zero to be exerted on a third close to an object that is suspended by a string. charged particle it must be placed: If the object is attracted toward the rod we can Answer: midway between A and B conclude: 31. Charge Q is spread uniformly along the Answer: none of the above (choices: object + circumference of a circle of radius R. A point charged, object is – charged, object is an particle with charge q is placed at the center of insulator, object is a conductor) this circle. The total force exerted on the 16. Two uncharged metal spheres, L and M, are in particle can be calculated by Coulomb’s law: contact. A negatively charged rod is brought Answer: the result of the calculation is zero close to L, but not touching it. The two spheres 32. Two particles, each with charge Q, and a third are slightly separated and the rod is then particle, with charge q, are placed at the withdrawn. As a result: vertices of an equilateral triangle. The total Answer: L is negative and M is positive force on the particle with charge q is: 17. A positively charged metal sphere A is brought Answer: perpendicular to the bottom side of the into contact with an uncharged metal sphere B. As triangle a result: 33. A particle with charge Q is on the y axis a Answer: both spheres are positively charged distance a from the origin and a particle with 18. The leaves of a positively charged electroscope charge q is on the x axis a distance d from the diverge more when an object is brought near the origin. The value of d for which the x component knob of the electroscope. The object must be: of the force on the second particle is the Answer: positively charged greatest is: 19. A negatively charged rubber rod is brought near Answer: a/√2 the knob of a positively charged electroscope. 34. In the Rutherford model of the hydrogen atom, a The result is that: proton (mass M, charge Q) is the nucleus and an Answer: the electroscope leaves will tend to electron (mass m, charge q) moves around the collapse proton in a circle of radius r. Let k denote the 20. An electroscope is charged by induction using a Coulomb force constant (1/4π60) and G the glass rod that has been made positive by rubbing universal gravitational constant. The ratio of it with silk. The electroscope leaves: the electrostatic force to the gravitational Answer: gain electrons force between electron and proton is: 21. Consider the following procedural steps: Answer: kQq/GMm 1. ground an electroscope 35. A particle with a charge of 5 × 10^−6 C and a 2. remove the ground from the electroscope mass of 20 g moves uniformly with a speed of 7 3. touch a charged rod to the electroscope m/s in a circular orbit around a stationary 4. bring a charged rod near, but not particle with a charge of −5 × 10^−6 C. The radius touching, the electroscope of the orbit is: 5. remove the charged rod Answer: 0.23 m ------------------------------------------------PAGE 1-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS 36. Charge is distributed uniformly on the surface of 53. Positive charge Q is uniformly distributed on a a spherical balloon (an insulator). A point semicircular rod. What is the direction of the particle with charge q is inside. The electrical electric field at point P, the center of the force on the particle is greatest when: semicircle? Answer: it is anywhere inside (the force is Answer: to the right zero everywhere) 54. Positive charge +Q is uniformly distributed on 37. Charge is distributed on the surface of a the upper half a semicircular rod and negative spherical conducting shell. A point particle with charge −Q is uniformly distributed on the lower charge q is inside. If polarization effects are half. What is the direction of the electric field negligible the electrical force on the particle at point P, the center of the semicircle? is greatest when: Answer: downwards Answer: it is near the inside surface of the 55. Positive charge +Q is uniformly distributed on balloon the upper half a rod and negative charge −Q is 38. An electric field is most directly related to: uniformly distributed on the lower half. What is Answer: the force acting on a test charge the direction of the electric field at point P, 39. As used in the definition of electric field, a on the perpendicular bisector of the rod? “test charge”: Answer: downwards Answer: none of the above B (choices: has zero 56. The electric field due to a uniform distribution charge, has charge of magnitude 1 C, has charge of charge on a spherical shell is zero: of magnitude 1.6 × 10^−19 C, must be an electron) Answer: only inside the shell 40. Experimenter A uses a test charge q0 and 57. A charged particle is placed in an electric field experimenter B uses a test charge −2q0 to measure that varies with location. No force is exerted on an electric field produced by stationary charges. this charge: A finds a field that is: Answer: at locations where the electric field Answer: the same in both magnitude and is zero direction as the field found by B 58. An electron traveling north enters a region where 41. The units of the electric field are: the electric field is uniform and points west. Answer: N/C The electron: 42. What kind of files are stored with the.mat Answer: veers east extension? 59. A charged particle is placed in an electric field Answer: J/(C·m) that varies with location. No force is exerted on 43. Electric field lines are: this charge: Answer: none of the above (choices: trajectories Answer: slows down of a test charge, vectors in the direction of 60. An electric dipole consists of a particle with a the electric field, from closed loops, cross each charge of +6 × 10^−6 C at the origin and a other in the region between two point charges) particle with a charge of −6 × 10^−6 C on the x 44. Two thin spherical shells, one with radius R and axis at x = 3 × 10^−3 m. Its dipole moment is: the other with radius 2R, surround an isolated Answer: 1.8 × 10^−8 C·m, in the negative x- charged point particle. The ratio of the number direction of field lines through the larger sphere to the 61. The force exerted by a uniform electric field on number through the smaller is: a dipole is: Answer: 1 Answer: none of the above (choices: parallel to 45. A certain physics textbook shows a region of space the dipole moment, perpendicular to the dipole in which two electric field lines cross each moment, parallel to the electric field, other. We conclude that: perpendicular to the electric field) Answer: the author made a mistake 62. An electric field exerts a torque on a dipole 46. Choose the correct statement concerning electric only if: field lines: Answer: the field is not parallel to the dipole Answer: field lines are close together where the moment field is larg 63. The torque exerted by an electric field on a 47. The electric field at a distance of 10 cm from an dipole is: isolated point particle with a charge of 2 × 10^−9 Answer: perpendicular to both the field and C is: dipole moment Answer: 1800 N/C 64. When the dipole moment of a dipole in a uniform 48. An isolated charged point particle produces an electric field rotates to become more nearly electric field with magnitude E at a point 2 m aligned with the field: away from the charge. A point at which the field Answer: the field does positive work and the magnitude is E/4 is: potential energy decreases Answer: 4 m away from the particle 65. The purpose of Milliken’s oil drop experiment was 49. An isolated charged point particle produces an to determine: electric field with magnitude E at a point 2 m Answer: the charge of an electron away. At a point 1 m from the particle the 66. A total charge of 6.3×10^−8 C is distributed magnitude of the field is: uniformly throughout a 2.7-cm radius sphere. The Answer: 4E volume charge density is: 50. Two point particles, with a charges of q1 and q2, Answer: 7.6 × 10^−4 C/m^3 are placed a distance r apart. The electric field 67. Charge is placed on the surface of a 2.7-cm radius is zero at a point P between the particles on the isolated conducting sphere. The surface charge line segment connecting them. We conclude that: density is uniform and has the value 6.9 × 10^−6 Answer: q1 and q2 must have the same sign but C/m^2. The total charge on the sphere is: may have different magnitudes Answer: 6.3 × 10^-8 C 51. Two charged point particles are located at two 68. A spherical shell has an inner radius of 3.7 cm vertices of an equilateral triangle and the and an outer radius of 4.5 cm. If charge is electric field is zero at the third vertex. We distributed uniformly throughout the shell with conclude: a volume density of 6.1 × 10^−4 C/m^3 the total Answer: at least one other charged particle is charge is: present Answer: 0.1 uC 52. Two point particles, with the same charge, are 69. A charged point particle is placed at the center located at two vertices of an equilateral of a spherical Gaussian surface. The electric triangle. A third charged particle is placed so flux ΦE is changed if: the electric field at the third vertex is zero. Answer: the point charge is moved to just outside The third particle must: the sphere Answer: be on the perpendicular bisector of the 70. Choose the INCORRECT statement: line joining the first two charges (I) Gauss’ law can be derived from Coulomb’s law ------------------------------------------------PAGE 2-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS (II) Gauss’ law states that the net number conductor and allowed to touch its inner surface. of lines crossing any closed surface in an After the ball is removed, it will have: outward direction is proportional to the net Answer: no appreciable charge charge enclosed within the surface 85. A spherical conducting shell has charge Q. A (III) Coulomb’s law can be derived from particle with charge q is placed at the center of Gauss’ law and symmetry the cavity. The charge on the inner surface of (IV) Gauss’ law applies to a closed surface the shell and the charge on the outer surface of of any shape the shell, respectively, are: (V) According to Gauss’ law, if a closed Answer: -q, Q + q surface encloses no charge, then the 86. An electron moves from point i to point f, in the electric field must vanish everywhere on the direction of a uniform electric field. During surface this displacement: Answer: V only Answer: the work done by the field is negative 71. The outer surface of the cardboard center of a and the potential energy of the electron-field paper towel roll: system increases Answer: cannot be a Gaussian surface because it 87. A particle with a charge of 5.5 × 10^−8 C is 3.5 is not a closed surface. cm from a particle with a charge of −2.3 × 10^−8 72. A physics instructor in an anteroom charges an C. The potential energy of this two-particle electrostatic generator to 25 µC, then carries it system, relative to the potential energy at into the lecture hall. The net electric flux in infinite separation, is: N·m^2/C through the lecture hall walls is: Answer: -3.2 × 10^-4 J Answer: 2.8 × 10^6 88. Two identical particles, each with charge q, are 73. A point particle with charge q is placed inside placed on the x axis, one at the origin and the the cube but not at its center. The electric flux other at x = 5 cm. A third particle, with charge through any one side of the cube: −q, is placed on the x axis so the potential Answer: cannot be computed using Gauss’ law energy of the three-particle system is the same 74. A point particle with charge q is at the center as the potential energy at infinite separation. of a Gaussian surface in the form of a cube. The Its x coordinate is: electric flux through any one face of the cube Answer: 13 cm is: 89. If 500 J of work are required to carry a charged Answer: q/6ε0 particle between two points with a potential 75. A conducting sphere of radius 0.01 m has a charge difference of 20 V, the magnitude of the charge of 1.0 × 10^−9 C deposited on it. The magnitude on the particle is: of the electric field in N/C just outside the Answer: 12.5 C surface of the sphere is: 90. During a lightning discharge, 30 C of charge move Answer: 900 through a potential difference of 1.0 × 108 V in 76. 10 C of charge are placed on a spherical 2.0 × 10^−2 s. The energy released by this conducting shell. A particle with a charge of −3 lightning bolt is: C is placed at the center of the cavity. The net Answer: 3.0 × 10^9 J charge on the inner surface of the shell is: 91. Two particle with charges Q and −Q are fixed at Answer: +3 C the vertices of an equilateral triangle with 77. 10 C of charge are placed on a spherical sides of length a. If k = 1/4πε0, the work conducting shell. A particle with a charge of −3 required to move a particle with charge q from C is placed at the center of the cavity. The net the other vertex to the center of the line joining charge on the inner surface of the shell is: the fixed particles is: Answer: +7 C Answer: 0 78. Charge Q is distributed uniformly throughout an 92. An electron is accelerated from rest through a insulating sphere of radius R. The magnitude of potential difference V. Its final speed is the electric field at a point R/2 from the center proportional to: is: Answer: √V Answer: Q/8πε0R^2 93. Two large parallel conducting plates are 79. Positive charge Q is distributed uniformly separated by a distance d, placed in a vacuum, throughout an insulating sphere of radius R, and connected to a source of potential difference centered at the origin. A particle with positive V. An oxygen ion, with charge 2e, starts from charge Q is placed at x = 2R on the x axis. The rest on the surface of one plate and accelerates magnitude of the electric field at x = R/2 on the to the other. If e denotes the magnitude of the x axis is: electron charge, the final kinetic energy of this Answer: Q/72πε0R^2 ion is: 80. Charge Q is distributed uniformly throughout a Answer: 2eV spherical insulating shell. The net electric flux 94. An electron volt is: in N·m^2/C through the inner surface of the shell Answer: the energy gained by an electron in is: moving through a potential difference of 1 volt Answer: 0 95. An electron has charge −e and mass me. A proton 81. A long line of charge with λf charge per unit has charge e and mass 1840me. A “proton volt” is length runs along the cylindrical axis of a equal to: cylindrical shell which carries a charge per unit Answer: 1 eV length of λc. The charge per unit length on the 96. Two conducting spheres, one having twice the inner and outer surfaces of the shell, diameter of the other, are separated by a distance respectively are: large compared to their diameters. The smaller Answer: -λf and λc + λf sphere (1) has charge q and the larger sphere (2) 82. Charge is distributed uniformly on the surface of is uncharged. If the spheres are then connected a large flat plate. The electric field 2 cm from by a long thin wire: the plate is 30 N/C. The electric field 4 cm from Answer: 1 and 2 have the same potential the plate is: 97. A conducting sphere with radius R is charged until Answer: 30 N/C the magnitude of the electric field just outside 83. A particle with charge Q is placed outside a large its surface is E. The electric potential of the neutral conducting sheet. At any point in the sphere, relative to the potential far away, is: interior of the sheet the electric field produced Answer: ER by charges on the surface is directed: 98. A hollow metal sphere is charged to a potential Answer: toward Q V. The potential at its center is: 84. A hollow conductor is positively charged. A small Answer: V uncharged metal ball is lowered by a silk thread 99. Positive charge is distributed uniformly through a small opening in the top of the throughout a non-conducting sphere. The highest electric potential occurs: ------------------------------------------------PAGE 3-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS Answer: at the center 119. Let Q denote charge, V denote potential 100. Eight identical spherical raindrops are each at difference, and U denote stored energy. Of these a potential V , relative to the potential far quantities, capacitors in parallel must have the away. They coalesce to make one spherical same: raindrop whose potential is: Answer: V only Answer: 4V 120. Capacitors C1 and C2 are connected in series and 101. A metal sphere carries a charge of 5 × 10^−9 C a potential difference is applied to the and is at a potential of 400 V, relative to the combination. If the capacitor that is equivalent potential far away. The potential at the center to the combination has the same potential of the sphere is: difference, then the charge on the equivalent Answer: 400 V capacitor is the same as: 102. A conducting sphere has charge Q and its electric Answer: the charge on C1 potential is V, relative to the potential far 121. Two identical capacitors are connected in series away. If the charge is doubled to 2Q, the and two, each identical to the first, are potential is: connected in parallel. The equivalent capacitance Answer: 2V of the series connection is __ the equivalent 103. In a certain region of space the electric capacitance of parallel connection. potential increases uniformly from east to west Answer: one-fourth and does not vary in any other direction. The 122. Two identical capacitors, each with capacitance electric field: C, are connected in parallel and the combination Answer: points east and does not vary with is connected in series to a third identical position capacitor. The equivalent capacitance of this 104. If the electric field is in the positive x arrangement is: direction and has a magnitude given by E = Cx^2, Answer: 2C/3 where C is a constant, then the electric potential 123. A 2-µF and a 1-µF capacitor are connected in is given by V =: series and charged from a battery. They store Answer: −Cx^3/3 charges P and Q, respectively. When disconnected 105. The work required to carry a particle with a and charged separately using the same battery, charge of 6.0 C from a 5.0-V equipotential surface they have charges R and S, respectively. Then: to a 6.0-V equipotential surface and back again Answer: R > S > Q = P to the 5.0-V surface is: 124. Capacitors A and B are identical. Capacitor A is Answer: 0 charged so it stores 4 J of energy and capacitor 106. The equipotential surfaces associated with a B is uncharged. The capacitors are then connected charged point particle are: in parallel. The total stored energy in the Answer: concentric spheres centered at the capacitors is now: particle Answer: 2 J 107. The capacitance of a parallel-plate capacitor is: 125. A battery is used to charge a parallel-plate Answer: proportional to the plate area capacitor, after which it is disconnected. Then 108. The capacitance of a parallel-plate capacitor can the plates are pulled apart to twice their be increased by: original separation. This process will double Answer: decreasing the plate separation the: 109. If both the plate area and the plate separation Answer: stored energy of a parallel-plate capacitor are doubled, the 126. A parallel-plate capacitor, with air dielectric, capacitance is: is charged by a battery, after which the battery Answer: unchanged is disconnected. A slab of glass dielectric is 110. If the plate area of an isolated charged parallel- then slowly inserted between the plates. As it is plate capacitor is doubled: being inserted: Answer: the potential difference is halved Answer: a force attracts the glass into the 111. Pulling the plates of an isolated charged capacitor capacitor apart: 127. Units of a magnetic field might be: Answer: increases the potential difference Answer: kg/C·s 112. If the charge on a parallel-plate capacitor is 128. An electron moves in the negative x direction, doubled: through a uniform magnetic field in the negative Answer: the electric field is doubled y direction. The magnetic force on the electron 113. The capacitance of a spherical capacitor with is: inner radius a and outer radius b is proportional Answer: in the negative z direction to: 129. The magnetic force on a charged particle is in Answer: ab/(b - a) the direction of its velocity if: 114. The capacitance of a single isolated spherical Answer: never conductor with radius R is proportional to: 130. A magnetic field exerts a force on a charged Answer: R particle: 115. Two conducting spheres have radii of R1 and R2, Answer: if the particle is moving across the with R1 greater than R2. If they are far apart field lines the capacitance is proportional to: 131. The direction of the magnetic field in a certain Answer: R1R2/(R1 - R2) region of space is determined by firing a test 116. A battery is used to charge a series combination charge into the region with its velocity in of two identical capacitors. If the potential various directions in different trials. The field difference across the battery terminals is V and direction is: total charge Q flows through the battery during Answer: one of the directions of the velocity the charging process then the charge on the when the magnetic force is zero positive plate of each capacitor and the 132. An electron is moving north in a region where the potential difference across each capacitor are: magnetic field is south. The magnetic force Answer: Q and V/2, respectively exerted on the electron is: 117. A 2-µF and a 1-µF capacitor are connected in Answer: zero series and a potential difference is applied 133. A magnetic field CANNOT: across the combination. The 2-µF capacitor has: Answer: change the kinetic energy of a charged Answer: half the potential difference of the 1- particle µF capacitor 134. A proton (charge e), traveling perpendicular to 118. Let Q denote charge, V denote potential a magnetic field, experiences the same force as difference, and U denote stored energy. Of these an alpha particle (charge 2e) which is also quantities, capacitors in series must have the traveling perpendicular to the same field. The same: ratio of their speeds, vproton/valpha, is: Answer: Q only Answer: 2 ------------------------------------------------PAGE 4-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS 135. A hydrogen atom that has lost its electron is 152. A long straight cylindrical shell carries current moving east in a region where the magnetic field i parallel to its axis and uniformly distributed is directed from south to north. It will be over its cross section. The magnitude of the deflected: magnetic field is greatest: Answer: up Answer: at the outer surface of the shell 136. At one instant an electron is moving in the 153. The magnetic field B inside a long ideal solenoid positive x direction along the x axis in a region is independent of: where there is a uniform magnetic field in the Answer: the cross-sectional area of the solenoid positive z direction. When viewed from a point on 154. Two long ideal solenoids (with radii 20 mm and 30 the positive z axis, it subsequent motion is: mm, respectively) have the same number of turns Answer: counterclockwise around a circle in the of wire per unit length. The smaller solenoid is xy plane mounted inside the larger, along a common axis. 137. The direction of the magnetic field in a certain The magnetic field within the inner solenoid is region of space is determined by firing a test zero. The current in the inner solenoid must be: charge into the region with its velocity in Answer: the same as the current in the outer various directions in different trials. The field solenoid direction is: 155. Solenoid 2 has twice the radius and six times the Answer: one of the directions of the velocity number of turns per unit length as solenoid 1. when the magnetic force is zero The ratio of the magnetic field in the interior 138. An electron and a proton are both initially moving of 2 to that in the interior of 1 is: with the same speed and in the same direction at Answer: 6 90º to the same uniform magnetic field. They 156. A toroid with a square cross section carries experience magnetic forces, which are initially: current i. The magnetic field has its largest Answer: equal in magnitude but opposite in magnitude: direction Answer: just inside the toroid at its inner 139. A current is clockwise around the outside edge of surface this page and a uniform magnetic field is directed 157. The normal to a certain 1-m^2 area makes an angle parallel to the page, from left to right. If the of 60º with a uniform magnetic field. The magnetic magnetic force is the only force acting on the flux through this area is the same as the flux page, the page will turn so the right edge: through a second area that is perpendicular to Answer: moves toward you the field if the second area is: 140. The units of magnetic dipole moment are: Answer: 0.5 sq.m. Answer: ampere-meter^2 158. Suppose this page is perpendicular to a uniform 141. The magnetic torque exerted on a flat current- magnetic field and the magnetic flux through it carrying loop of wire by a uniform magnetic field is 5 Wb. If the page is turned by 30 around an B is: edge the flux through it will be: Answer: maximum when the plane of the loop is Answer: 4.3 Wb parallel to B 159. The units of motional emf are: 142. For a loop of current-carrying wire in a uniform Answer: tesla·meter^2/second magnetic field the potential energy is a minimum 160. Faraday’s law states that an induced emf is if the magnetic dipole moment of the loop is: proportional to: Answer: in the same direction as the field Answer: the rate of change of the magnetic flux 143. Lines of the magnetic field produced by a long 161. The emf that appears in Faraday’s law is: straight wire carrying a current are: Answer: around the boundary of the surface used Answer: circles that are concentric with the to compute the magnetic flux wire 162. The units of magnetic field strength are: 144. In an overhead straight wire, the current is Answer: ampere/meter north. The magnetic field due to this current, at 163. If the magnetic flux through a certain region is our point of observation, is: changing with time: Answer: west Answer: an emf must exist around the boundary 145. A wire carrying a large current i from east to 164. A square loop of wire lies in the plane of the west is placed over an ordinary magnetic compass. page. A decreasing magnetic field is directed The end of the compass needle marked “N” will into a page. The induced current in the loop is: point: Answer: clockwise Answer: south 165. As an externally generated magnetic field through 146. The magnetic field outside a long straight a certain conducting loop increases in magnitude, current-carrying wire depends on the distance R the field produced at points inside the loop by from the wire axis according to: the current induced in the loop must be: Answer: 1/R Answer: directed opposite to the applied field 147. Two long parallel straight wires carry equal 166. A circular loop of wire rotates about a diameter currents in opposite directions. At a point in a magnetic field that is perpendicular to the midway between the wires, the magnetic field they axis of rotation. Looking in the direction of the produce is: field at the loop the induced current is: Answer: non-zero and perpendicular to the plane Answer: sometimes clockwise and sometimes of the two wires counterclockwise 148. Two parallel wires carrying equal currents of 10 167. A rectangular loop of wire has area A. It is A attract each other with a force of 1 mN. If placed perpendicular to a uniform magnetic field both currents are doubled, the force of B and then spun around one of its sides at attraction will be: frequency f. The maximum induced emf is: Answer: 4 mN Answer: 2πBAf 149. Two parallel long wires carry the same current 168. A rectangular loop of wire is placed and repel each other with a force F per unit perpendicular to a uniform magnetic field and length. If both these currents are doubled and then spun around one of its sides at frequency f. the wire separation tripled, the force per unit The induced emf is a maximum when: length becomes: Answer: the flux is zero Answer: 4F/3 169. A single loop of wire with a radius of 7.5 cm 150. A constant current is sent through a helical coil. rotates about a diameter in a uniform magnetic The coil: field of 1.6 T. To produce a maximum emf of 1.0 Answer: tends to get shorter V, it should rotate at: 151. Helmholtz coils are commonly used in the Answer: 35 rad/s laboratory because the magnetic field between 170. A flat coil of wire, having 5 turns, has an them: inductance L. The inductance of a similar coil Answer: is nearly uniform having 20 turns is: Answer: 16L ------------------------------------------------PAGE 5-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS ELECTRIC CIRCUITS 190. For an ohmic substance, the electron drift velocity is proportional to: 171. A car battery is rated at 80 A · h. An ampere- Answer: the electric field in the sample hour is a unit of: 191. You wish to triple the rate of energy dissipation Answer: charge in a heating device. To do this you could triple: 172. Current is a measure of: Answer: the resistance keeping the current the Answer: amount of charge that moves past a same point per unit time 192. A student kept her 60-watt, 120-volt study lamp 173. A 10-ohm resistor has a constant current. If 1200 turned on from 2:00 PM until 2:00 AM. How many C of charge flow through it in 4 minutes what is coulombs of charge went through it? the value of the current? Answer: 21,600 Answer: 15 A 193. An certain resistor dissipates 0.5 W when 174. Conduction electrons move to the right in a connected to a 3 V potential difference. When certain wire. This indicates that: connected to a 1 V potential difference, this Answer: the current density and electric field resistor will dissipate: both point left Answer: 0.056 W 175. Two wires made of different materials have the 194. The mechanical equivalent of heat is 1 cal = 4.18 same uniform current density. They carry the same J. The specific heat of water is 1 cal/g·K. An current only if: electric immersion water heater, rated at 400 W, Answer: their cross-sectional areas are the should heat a kilogram of water from 10ºC to 30ºC same in about: 176. A wire with a length of 150 m and a radius of Answer: 3.5 min 0.15 mm carries a current with a uniform current 195. It is better to send 10, 000 kW of electric power density of 2.8 × 10^7 A/m^2. The current is: long distances at 10, 000 V rather than at 220 V Answer: 2.0 A because: 177. In a conductor carrying a current we expect the Answer: there is less heating in the transmission electron drift speed to be: wires Answer: much less than the average electron 196. Suppose the electric company charges 10 cents per speed kW·h. How much does it cost to use a 125 W lamp 178. Two substances are identical except that the 4 hours a day for 30 days? electron mean free time for substance A is twice Answer: $1.50 the electron mean free time for substance B. If 197. The mechanical equivalent of heat is 1 cal = 4.18 the same electric field exists in both substances J. A heating coil, connected to a 120-V source, the electron drift speed in A is: provides 60,000 calories in 10 minutes. The Answer: twice that in B current in the coil is: 179. The current is zero in a conductor when no Answer: 3.5 A potential difference is applied because: 198. “The sum of the currents into a junction equals Answer: for every electron with a given velocity the sum of the currents out of the junction” is there is another with a velocity of equal a consequence of: magnitude and opposite direction Answer: conservation of charge 180. If the potential difference across a resistor is 199. “The sum of the emf’s and potential differences doubled: around a closed loop equals zero” is a consequence Answer: only the current is doubled of: 181. A cylindrical copper rod has resistance R. It is Answer: conservation of energy reformed to twice its original length with no 200. Four wires meet at a junction. The first carries change of volume. Its new resistance is: 4 A into the junction, the second carries 5 A out Answer: 4R of the junction, and the third carries 2 A out of 182. The resistance of a rod does NOT depend on: the junction. The fourth carries: Answer: the shape of its (fixed) cross-sectional Answer: 3 A into the junction area 201. In the context of the loop and junctions rules 183. A certain wire has resistance R. Another wire, of for electrical circuits a junction is: the same material, has half the length and half Answer: where three or more wires are joined the diameter of the first wire. The resistance of 202. For any circuit the number of independent the second wire is: equations containing emf’s, resistances, and Answer: 2R currents equals: 184. A nichrome wire is 1 m long and 1 × 10^−6 m^2 in Answer: the number of branches cross-sectional area. When connected to a 203. If a circuit has L closed loops, B branches, and potential difference of 2 V, a current of 4 A J junctions the number of independent loop exists in the wire. The resistivity of this equations is: nichrome is: Answer: B - J + 1 Answer: 5 × 10^-7 Ω·m 204. A total resistance of 3.0 Ω is to be produced by 185. Two conductors are made of the same material and combining an unknown resistor R with a 12 Ω have the same length. Conductor A is a solid wire resistor. What is the value of R and how is it to of diameter 1 m. Conductor B is a hollow tube of be connected to the 12 Ω resistor? inside diameter 1 m and outside diameter 2 m. The Answer: 4.0 Ω, parallel ratio of their resistance, RA/RB, is: 205. By using only two resistors, R1 and R2, a student Answer: 3 is able to obtain resistances of 3 Ω, 4 Ω, 12 Ω, 186. Two wires are made of the same material and have and 16 Ω. The values of R1 and R2 (in ohms) are: the same length but different radii. They are Answer: 4, 12 joined end-to-end and a potential difference is 206. Nine identical wires, each of diameter d and maintained across the combination. Of the length L, are connected in parallel. The following the quantity that is the same for both combination has the same resistance as a single wires is: similar wire of length L but whose diameter is: Answer: current Answer: 3d 187. For an ohmic substance the resistivity is the 207. Nine identical wires, each of diameter d and proportionality constant for: length L, are connected in series. The Answer: current density and electric field combination has the same resistance as a single 188. For an ohmic resistor, resistance is the similar wire of length L but whose diameter is: proportionality constant for: Answer: d/3 Answer: current and potential difference 208. Two wires made of the same material have the same 189. For an ohmic substance, the resistivity depends lengths but different diameters. They are on: connected in parallel to a battery. The quantity Answer: the electron mean free time that is NOT the same for the wires is: Answer: the current ------------------------------------------------PAGE 6-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS 209. The resistance of resistor 1 is twice the is half the final value. The time constant for resistance of resistor 2. The two are connected the process is about: in parallel and a potential difference is Answer: 14 ms maintained across the combination. Then: 227. A charged capacitor and an inductor are connected Answer: the current in 1 is half that in 2 in series. At time t = 0 the current is zero, but 210. The resistance of resistor 1 is twice the the capacitor is charged. If T is the period of resistance of resistor 2. The two are connected the resulting oscillations, the next time after in series and a potential difference is t = 0 that the current is a maximum is: maintained across the combination. Then: Answer: T/4 Answer: the potential difference across 1 is 228. A charged capacitor and an inductor are connected twice that across 2 in series. At time t = 0 the current is zero, but 211. Resistor 1 has twice the resistance of resistor the capacitor is charged. If T is the period of 2. The two are connected in series and a potential the resulting oscillations, the next time after difference is maintained across the combination. t = 0 that the charge on the capacitor is a The rate of thermal energy generation in 1 is: maximum is: Answer: half that in 2 Answer: T/2 212. The emf of a battery is equal to its terminal 229. A capacitor in an LC oscillator has a maximum potential difference: potential difference of 15 V and a maximum energy Answer: only when there is no current in the of 360 µJ. At a certain instant the energy in the battery capacitor is 40 µJ. At that instant what is the 213. Two identical batteries, each with an emf of 18 potential difference across the capacitor? V and an internal resistance of 1 Ω, are wired in Answer: 5 V parallel by connecting their positive terminals 230. Which of the following has the greatest effect in together and connecting their negative terminals decreasing the oscillation frequency of an LC together. The combination is then wired across a circuit? Using instead: 4-Ω resistor. The current in the 4-Ω resistor is: Answer: 2L and 2C Answer: 4.0 A 231. We desire to make an LC circuit that oscillates 214. A 120-V power line is protected by a 15-A fuse. at 100 Hz using an inductance of 2.5 H. We also What is the maximum number of “120 V, 500 W” light need a capacitance of: bulbs that can be operated at full brightness Answer: 1 uF from this line? 232. An LC circuit has an oscillation frequency of Answer: 3 10^5 Hz. If C = 0.1 µF, then L must be about: 215. A resistor with resistance R1 and a resistor with Answer: 25 uH resistance R2 are connected in parallel to an 233. Radio receivers are usually tuned by adjusting ideal battery with emf E. The rate of thermal the capacitor of an LC circuit. If C = C1 for a energy generation in the resistor with resistance frequency of 600 kHz, then for a frequency of R1 is: 1200 kHz one must adjust C to: Answer: E^2/R1 Answer: C1/4 216. Resistor 1 has twice the resistance of resistor 234. An LC series circuit with an inductance L and a 2. They are connected in parallel to a battery. capacitance C has an oscillation frequency f. Two The ratio of the thermal energy generation rate inductors, each with inductance L, and two in 1 to that in 2 is: capacitors, each with capacitance C, are all Answer: 1:2 wired in series and the circuit is completed. The 217. A series circuit consists of a battery with oscillation frequency is: internal resistance r and an external resistor R. Answer: f If these two resistances are equal (r = R) then 235. The electrical analog of a spring constant k is: the thermal energy generated per unit time by the Answer: 1/C internal resistance r is: 236. In an oscillating LC circuit, the total stored Answer: the same as by R energy is U. The maximum energy stored in the 218. A certain galvanometer has a resistance of 100 Ω capacitor during one cycle is: and requires 1 mA for full scale deflection. To Answer: U make this into a voltmeter reading 1 V full scale, 237. In an oscillating LC circuit, the total stored connect a resistance of: energy is U and the maximum charge on the Answer: 900 Ω in series capacitor is Q. When the charge on the capacitor 219. To make a galvanometer into an ammeter, connect: is Q/2, the energy stored in the inductor is: Answer: a low resistance in parallel Answer: 3U/4 220. A certain voltmeter has an internal resistance of 238. At time t = 0 the charge on the 50-µF capacitor 10,000 Ω and a range from 0 to 100 V. To give it in an LC circuit is 15 µC and there is no current. a range from 0 to 1000 V, one should connect: If the inductance is 20 mH the maximum current Answer: 90,000 Ω in series is: 221. A certain ammeter has an internal resistance of Answer: 15 mA 1 Ω and a range from 0 to 50 mA. To make its range 239. An LC circuit has a capacitance of 30 µF and an from 0 to 5 A, use: inductance of 15 mH. At time t = 0 the charge on Answer: a resistance of 1/99 Ω in parallel the capacitor is 10 µC and the current is 20 mA. 222. A galvanometer has an internal resistance of 12 The maximum charge on the capacitor is: Ω and requires 0.01 A for full scale deflection. Answer: 17 uC To convert it to a voltmeter reading 3 V full 240. An RLC circuit has a resistance of 200 Ω and an scale, one must use a series resistance of: inductance of 15 mH. Its oscillation frequency is Answer: 288 Ω 7000 Hz. At time t = 0 the current is 25 mA and 223. A certain voltmeter has an internal resistance of there is no charge on the capacitor. After five 10,000 Ω and a range from 0 to 12 V. To extend complete cycles the current is: its range to 120 V, use a series resistance of: Answer: 2.1 × 10^-4 A Answer: 90,000 Ω 241. An RLC circuit has an inductance of 25 mH and a 224. The time constant RC has units of: capacitance of 5.0 µF. The charge on the capacitor Answer: seconds does NOT oscillate but rather decays 225. A charged capacitor is being discharged through exponentially to zero. The resistance in the a resistor. At the end of one time constant the circuit must be: charge has been reduced by (1 − 1/e) = 63% of its Answer: greater than or equal to 20,000 Ω initial value. At the end of two time constants 242. A series circuit with an inductance of 15 mH, a the charge has been reduced by what percent of capacitance of 35 µF, and a resistance of 5.0 Ω its initial value? contains a sinusoidal source of emf with a Answer: 86% frequency of 500 Hz. The frequency with which the 226. A certain capacitor, in series with a resistor, charge on the capacitor oscillates is: is being charged. At the end of 10 ms its charge Answer: 500 Hz ------------------------------------------------PAGE 7-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS 243. The rapid exponential decay in just a few cycles Answer: true power of the charge on the plates of capacitor in an 265. Which of the following refers to a parallel RLC circuit might be due to: circuit? Answer: a large resistance Answer: The current through any one element is 244. The angular frequency of a certain RLC series less than the source current circuit is ω0. A source of sinusoidal emf, with 266. As the impedance increases, the admittance: angular frequency 2ω, is inserted into the Answer: decreases circuit. After transients die out the angular 267. The power consumed in a circuit element will be frequency of the current oscillations is: least when the phase difference between the Answer: 2ω0 current and voltage is 245. In a purely capacitive circuit the current: Answer: 90 degrees Answer: leads the voltage by one-fourth of a 268. Form Factor is the ratio of cycle Answer: r.m.s. value / average value 246. In a purely resistive circuit the current: 269. Capacitive reactance is more when Answer: is in phase with the voltage Answer: Capacitance is less and frequency of 247. In a purely inductive circuit, the current lags supply is less the voltage by: 270. In any A.C. circuit always Answer: one-fourth of a cycle Answer: Apparent power is more than actual power 248. A 35-µF capacitor is connected to a source of 271. The safest value of current the human body can sinusoidal emf with a frequency of 400 Hz and a carry for more than 3 second is: maximum emf of 20 V. The maximum current is: Answer: 9 mA Answer: 1.8 A 272. The purpose of a parallel circuit resonance is to 249. The impedance of an RLC series circuit is magnify: definitely increased if: Answer: voltage Answer: R increases 273. A parallel AC circuit in resonance will: 250. An RLC series circuit has R = 4 Ω, XC = 3 Ω, and Answer: have high impedance XL = 6 Ω. The impedance of this circuit is: 274. The power is measured in terms of decibels in Answer: 5 Ω case of: 251. An RL series circuit is connected to an ac Answer: Electronic equipment generator with a maximum emf of 20 V. If the 275. In a pure inductive circuit if the supply maximum potential difference across the resistor frequency is reduced to 1/2, the current will is 16 V, then the maximum potential difference Answer: be doubled across the inductor is: 276. Wire-wound resistors are unsuitable for use at Answer: 12 V high frequencies because they: 252. When the amplitude of the oscillator in a series Answer: Exhibit unwanted inductive and RLC circuit is doubled: capacitive effects Answer: the current amplitude is doubled 277. Which of the following waves has the highest value 253. When the frequency of the oscillator in a series of peak factor? RLC circuit is doubled: Answer: Half wave rectified sine wave Answer: the capacitive reactance is halved 278. In a series resonant circuit, the impedance of 254. In an RLC series circuit, the source voltage is the circuit is: leading the current at a given frequency f. If f Answer: Minimum is lowered slightly, then the circuit impedance 279. In series resonant circuit, increasing inductance will: to its twice value and reducing capacitance to Answer: decrease its half value: 255. An RLC series circuit has L = 100 mH and C = 1 Answer: Will increase the selectivity of the µF. It is connected to a 1000-Hz source and the circuit source emf is found to lead the current by 75◦. 280. In the case of an unsymmetrical alternating The value of R is: current the average value must always be taken Answer: 126 Ω over: 256. In a sinusoidally driven series RLC circuit the Answer: The whole cycle current lags the applied emf. The rate at which 281. A heater is rated as 230 V, 10 kW, A.C. The value energy is dissipated in the resistor can be 230 V refers to: increased by: Answer: rms voltage Answer: decreasing the capacitance and making no 282. The series and parallel resonance on L-C circuit’ other changes differs in that 257. An RLC series circuit, connected to a source E, Answer: Series resistance needs a low-resistance is at resonance. Then: source for sharp rise in current Answer: the voltage across R equals the applied 283. In a series L-C circuit at the resonant frequency voltage the: 258. The rms value of an ac current is: Answer: Current is maximum Answer: that steady current that produces the 284. In a three-phase supply floating neutral is same rate of heating in a resistor as the actual undesirable because it way give rise to: current Answer: Unequal line voltages across the load 259. An ac generator producing 10 V (rms) at 200 rad/s 285. In a loss-free R-L-C circuit the transient is connected in series with a 50-Ω resistor, a current is: 400-mH inductor, and a 200-µF capacitor. The rms Answer: Sinusoidal voltage (in volts) across the capacitor is: 286. Inductance affects the direct current flow: Answer: 3.4 Answer: At the time of turning on and off 260. The main reason that alternating current replaced 287. The effective resistance of an iron-cored choke direct current for general use is: working on ordinary supply frequency is more than Answer: ac voltages may be conveniently its true resistance because of transformed Answer: Iron loss in core 261. The power factor at resonance in R-L-C series 288. Skin effect occurs when a conductor carries circuit is: current at ____ frequencies. Answer: unity Answer: High 262. In an AC. circuit, a low value of kVAR compared 289. Capacitive susceptance is a measure of: with kW indicates Answer: A purely capacitive circuit’s ability to Answer: High power factor pass current 263. The power factor of a D.C. circuit is always 290. A 3-phase load is balanced if all the three phases Answer: Unity have the same: 264. The product of apparent power and cosine of the Answer: Impedance and power factor phase angle between circuit voltage and current is ------------------------------------------------PAGE 8-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS 291. In the two wattmeter method, the algebraic sum of Answer: Chemical effects the readings of two wattmeters will indicate true 313. A wire carries an AC current of 3cos(100*pi*t) A. power only if: What is the average current over 6 s? Answer: The load is balanced Answer: 0 A 292. In a balanced three-phase load, the current in 314. What is the relationship between the line the neutral wire is: current, I1 and the coil current, Ic in a balanced Answer: Zero delta system? 293. In a balanced three-phase system, the sum of the Answer: I1 = sqrt(3)Ic instantaneous voltages of the three phases is: 315. A balanced, three-phase, wye-connected system has Answer: Zero three identical phase impedances. The line-to- 294. The wattmeter method is used to measure power in line voltage is 240 V. The line-to-neutral a three-phase load. The wattmeter readings are current is 41 A. The power factor is 0.8 leading. 400W and -35W. Find the power factor. Most nearly, the total apparent power in the Answer: 0.43 system is 295. The wattmeter reading while measuring the Answer: 14 – j10 kVA reactive power with wattmeter is? 316. The most important advantage of using electrical Answer: VLILsinØ or √3VLILsinØ energy in the form of ac is 296. When a lead acid battery is being charged, the Answer: transformation of voltage is possible in specific gravity of the electrolyte will: case of ac only. Answer: increase 317. If two sinusoids of the same frequency but of 297. A 3 V DC supply with an internal resistance of 2 different amplitudes and phase difference are Ω supplies a passive non-linear resistance added, the resultant is a characterized by the relation VNL = I2NL. The power Answer: sinusoid of the same frequency dissipated in the resistance is 318. In an RLC circuit, supplied from an ac source, Answer: 1 W the reactive power is proportional to the 298. An alternating voltage V = 150 sin(314)t is Answer: difference between the average energy supplied to a device which offers a resistance of stored in the electric field and that stored in 20 Ω in forward direction of electric current the magnetic field while preventing the flow of electric current in 319. A small capacitance is added to a highly inductive reverse direction. The form factor is: circuit, Answer: 1.57 Answer: the power factor will increase 299. The maximum power is delivered from a source to 320. In the two wattmeter method of power measurement, its load when the load resistance is ______ the one of the WM will show negative reading when the source resistance. load pf angle is strictly Answer: equal to Answer: greater than 60 degrees 300. If source impedance is complex, then maximum power transfer occurs when the load impedance is ELECTRIC MACHINES _______ the source impedance. Answer: complex conjugate of 321. Modern locomotive are powered by DC motors driven 301. If the source impedance is complex, then the by DC generators. These are, in turn, driven by condition for maximum power transfer is? diesel engines. Which of the following is the Answer: ZL = ZS* reason for using such a configuration instead of 302. A two-phase generator is connected to two 90 ohms AC generator-motor sets? load resistors. Each coil generates 120 V ac. A Answer: The DC configuration provided high torque common neutral line exists. How much current and good incremental power at low speeds, and flows through the common neutral line? performs equally well at high speeds. Answer: 1.77 A 322. In a DC motor, what is the definition of “field 303. A three-phase generator is connected to two 90 resistance”? ohms load resistors. Each coil generates 120 V Answer: It is the resistance of the excitation ac. A common neutral line exists. How much current circuit. flows through the common neutral line? 323. In a DC motor, which of the following does NOT Answer: 0 A cause sparking at a commutator? 304. Compare the total copper cross sections in terms Answer: high brush contact resistance of current-carrying capacity for a single-phase 324. The armature in a DC generator has one or more and a three-phase 120 V system with effective pairs of conductors or oils in which current is load resistance of 15 ohms. produce. In general, which of the following is Answer: single-phase 16 A; three-phase 8 A true about the amount of power produced? 305. Non-sinusoidal waveforms are made up of Answer: More coils give more power Answer: different sinusoidal waveforms 325. Which of the following limits the number of coils 306. The positive and negative halves of a complex that may be placed on the armature of a DC motor wave are symmetrical when: or generator? Answer: it contains odd harmonics Answer: coil to coil arcing due to the breakdown 307. In a 3-phase system, the __ harmonic has negative of insulation phase sequence of RBY 326. A DC system can be protected from lighting by Answer: 5th including a thyrite tube in the circuit that 308. A complex current wave is given by the equation connects the high-voltage line with the ground. i = 14sin(ωt) + 2sin(5ωt). The r.m.s. value of Which of the following is FALSE regarding a the current is ___ ampere. thyrite tube? Answer: 10 Answer: Its usable link melts at high voltages. 309. When a pure inductive coil is fed by a complex 327. The magnetic saturation curve limits the voltage voltage wave, its current wave at which a generator or motor can operate. Which Answer: shows less distortion of the following statements regarding saturation 310. Which of the following harmonic voltage curves is FALSE? components in a 3-phase system would be in phase Answer: Saturation does not depend upon the type with each other? of steel used in the poles. Answer: 2nd, 4th, 6th, etc 328. Series and shunt motors are connected like series 311. An alternating current with a frequency of 60 Hz and shunt generators, respectively. The term is passed through a moving coil galvanometer that refer to the manner in which the self excitation measures DC current. What will the galvanometer of the poles is connected to the unit. Which of reading be equal to? the following statements is FALSE? Answer: A negligible amount Answer: The torque curves of both aunt and series 312. Which of the following effects are generally less motors are not affected by the value of the for an alternating current than for a direct armature current. current? ------------------------------------------------PAGE 9-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS 329. In terms of efficiency, shunt and series motors 349. Which of the following losses is associated with or generators have similar characteristics. Which eddy currents in an electrical machine? of the following statements is FALSE? Answer: Iron loss Answer: The two types of motors have very similar 350. In a DC generator, what determines the direction efficiency curves. of induced EMF? 330. What is pole pitch? Answer: Direction of the magnetic field and Answer: the space on the stator allocated to one motion pole 351. Why are laminations used in the core of electrical 331. Which of the following statements regarding a machines? compound motor is FALSE? Answer: To reduce eddy current losses Answer: It has speed remains fairly constant when 352. What is the purpose of using a starter in a DC subjected to sudden loads. motor? 332. Which of the following does NOT contribute to Answer: To limit the starting current core losses in DC motors? 353. Which of the following is true about the slip in Answer: commutator losses an induction motor? 333. Which of the following are power losses in a DC Answer: it increases as the load increases motor? 354. What is the primary cause of hysteresis losses in Answer: all of these (I^2R losses, gear and electrical machines? frictional losses, hysteresis losses) Answer: Variable magnetic field in the core 334. Which of the following statements is FALSE 355. Which is the most widely used material in the regarding large DC motors? core of the transformer? Answer: Wave winding does not pass under all Answer: cold rolled grain oriented sheet steel poles at one time. 356. Separately excited dc generators are used in 335. Which of the following statements is FALSE about Answer: Ward Leonard’s system of speed control the operation of parallel shunt generators? 357. Maximum torque in dc series motor is limited by Answer: One large unit would be more expensive Answer: commutation than the use of several smaller ones, even if it 358. Hoists, cranes and battery powered vehicles use ran at full load at all times. _________ motors in the locomotive. 336. An AC alternator as a motor is called a Answer: dc series synchronous motor. Which of the following 359. There is an application which required pulsating statements regarding synchronous motors is FALSE? loads, punch presses. The most preferred machines Answer: The poles of a synchronous motor must be would be salient Answer: compound dc machine 337. Which of the following statements about induction 360. The manufacturer has mentioned a medium starting motors is FALSE? torque and 15% speed regulation. Which is the Answer: They are used to increase the line power most appropriate motor for this requirement? factor. Answer: dc shunt motor 338. A single-phase induction motor is not self- 361. Centrifugal pumps, fans-blowers use starting. Instead, auxiliary methods must be Answer: shunt as well as induction motor used, such as varying inductance, resistance and 362. Most commercial compound dc generator are capacitance. Which of the following is FALSE normally supplied by manufacturers as over regarding this situation? compound machines because Answer: Capacitor motors have lower starting Answer: degree of compounding can be adjusted by torque than completely sized single-phase diverters across series field induction motors. 363. Which of the following are applied with 339. A squirrel-cage motor has such low resistance differential compound motor? that it draws excessive currents when starting. Answer: Hoist Which of the following actions will NOT reduce 364. Most commercial compound dc generator are this problem? normally supplied by manufacturers as ______ Answer: Using a class A motor. compounded machines. 340. Electromagnetic torque in rotating electrical Answer: over machinery is present when 365. A 200 V dc motor has external resistances of Ra Answer: Both stator and rotor windings carry and Rf in armature and field circuits current respectively. The starting current is reduced 341. In a rotating electrical machine with 2 poles on when? the stator and 4 poles on the rotor, spaced Answer: Ra is maximum and Rf minimum equally, the net electromagnetic torque developed 366. Consider a DC generator running at the rated speed is of 2000 rpm, suddenly there is an insulator falls Answer: zero or no torque is developed on the field circuit and breaks it. Then 342. The interaction torque in a rotating electrical Answer: the motor stops in a few rounds machine depends on which of the following 367. The self-excited dc generator with gradual components? buildup of residual voltage and EMF corresponds Answer: sinδ, stator field strength, rotor field to strength Answer: positive feedback 343. Which of the following can be obtained by the 368. The critical resistance refers to equivalent circuit of an electrical machine? Answer: the resistance above which machine does Answer: Complete performance characteristics of not excite the machine 369. If a DC shunt generator fails to start, the most 344. For an electrical machine with C number of coils primitive action would be and P poles, the distance between the coils Answer: reversing field connection to armature connected by an equalizer ring is? 370. Flashing is used to Answer: 2C/P Answer: temporarily excite the field from a 345. Which of the following is the primary function of battery source for large DC generators a commutator in a DC machine? 371. The number of parallel paths in the armature is Answer: To reverse the current direction increased by 346. Which of the following is a characteristic of a Answer: increasing number of magnetic poles synchronous motor? 372. In a dc series generator, if the armature and Answer: It always operates at synchronous speed field connections are reversed, the generator 347. Which of the following is the primary advantage Answer: will stop of a 3-phase induction motor? 373. Small DC motors have best speed control by Answer: Simple construction and low cost Answer: armature voltage control 348. What is the primary function of the stator in a 374. To implement armature voltage control, it must be synchronous machine? ensured that Answer: To generate the magnetic field Answer: it is used on separately excited machine ------------------------------------------------PAGE 10-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS 375. The flux and the internally generated voltage of delivering a synchronous power of 0.5 pu to the a dc machine is a ________ function of its bus. If the prime-mover torque is increased by magneto-motive force. 1%, by how much will the synchronous power P Answer: non-linear change? 376. It is advised not to run dc series motor with no Answer: 1% (Explanation: dP/dδ = EVcosδ/X) load. Why? 397. A synchronous machine which is synchronized with Answer: Because zero torque at no load will make an infinite bus. If it is desired to obtain a speed infinite condition when the machine delivers the real 377. A student is given a differential compound motor power to the IBB without changing the field and he has been asked to make it start. How will excitation, then he try? Answer: reactive power will be consumed by the Answer: all of these (By shorting series field machine at start, To run as shunt motor at start, By 398. The phasor addition of stator and rotor mmfs in making rated current at start) a cylindrical rotor synchronous machine, is 378. An induction motor can be said analogous to possible because Answer: transformer Answer: mmfs are stationary with respect to each 379. A 3-phase induction motor with its rotor blocked other behaves similar to a 399. For the effective electromechanical energy Answer: transformer under short circuit of conversion in the device, the developed torque secondary terminals depends upon 380. The rated current in induction motor for a three Answer: stator field and rotor field and the phase system is 100A. What can be the no load torque angle estimated current for the machine? 400. In a synchronous machine, hunting is Answer: 12 A predominantly damped by 381. The no load current of the transformer is very Answer: copper losses of rotor less due to 401. Which of the following equation best represents Answer: mutual flux having low reluctance iron the mutual inductance between stator and rotor in core a single phase cylindrical rotor synchronous 382. The no load current of the induction motor is machine? (where θr= space angle between stator high due to and rotor field axis) Answer: long and high reluctance path between Answer: Msr=Mmaxcosθr stator and rotor 402. An electromechanical energy conversion device has 383. At no load induction motor has possible power cylindrical stator but salient pole rotor. If δ factor as is the angle between stator field and rotor field, Answer: 0.2 the average torque developed is proportional to 384. An induction motor when started on load, it does (A and B are constants) not accelerate up to full speed but runs at 1/7th Answer: Asinδ+Bsin2δ of the rated speed. The motor is said to be 403. Large stiffness coefficient represents Answer: Crawling Answer: motor speed remains practically constant 385. The great advantage of the double squirrel-cage 404. As the load angle is increased, degree of induction motor over single cage rotor is that stability its Answer: reduces Answer: starting current is lower 405. Synchronizing power is 386. The rotor of 3-phase slip ring induction motor is Answer: transient in nature fed from a 3-phase supply with its stator winding 406. Which of the following makes synchronizing power short circuited having rotor rotating clockwise to come to play in the machine? at a speed of Nr, then the Answer: Disturbance in power mover Answer: speed of air gap field w.r.t. stator is 407. Which of the following is/are used in synchronous Ns-Nr anticlockwise machines to maintain mechanical stability? 387. If the machine was operating at unity pf, then Answer: Damper winding the new excitation voltage will be 408. Electromagnetic torque is present in rotating Answer: greater than 1 pu machines when 388. Alternator compounding characteristic is obtained Answer: both stator and rotor windings carry by current Answer: keeping Vt constant 409. The operation of a synchronous motor operating on 389. The rating of the alternator is decided by constant excitation across infinite bus will not Answer: losses be stable if power angle δ? 390. The core losses in synchronous machine is _______ Answer: exceeds internal angle θ dependent. 410. In a synchronous motor the back emf peak set up Answer: voltage in the stator depends on 391. For a 3 phase 400V alternator having 0.5pu of Answer: rotor excitation synchronous reactance and its excitation voltage 411. Variation in the dc excitation of a synchronous of 1.2pu and Vt of 1pu. Then the power delivered motor causes variation in to the infinite bus is? Answer: armature current and power factor Answer: 2.4 pu 412. Which motor can conveniently operate at lagging 392. For a 3 phase 400V alternator supplying a load of as well as leading power factor? 0.8 pf lagging at an armature current of 1.1pu. Answer: Synchronous motor The power delivered to load is? 413. Steady state stability limit is defined as Answer: 0.88 pu maximum power flow possible through a particular 393. A 3 phase 400V salient pole alternator is running point without loss of stability when the at no-load. Suddenly the excitation is removed Answer: power is increased gradually then the net power in the machine is proportional 414. The supply voltage to an induction motor is to decreased by 10%. By what percentage, Answer: sin 2δ approximately, will the maximum torque decrease? 394. If the synchronous machine is connected to an Answer: 20% infinite bus of constant voltage Vt, through a 415. What is the principle of torque production in a transformed, a transmission line of reactance dc machine? ‘X’. Then power for a cylindrical machine is? Answer: Lorentz’s law Answer: P = (Ef*Vt sinδ)/(Xs + X) 416. The torque induced beyond the pole shoes in the 395. Maximum power in cylinder rotor alternator occurs DC machine is? at load angle of Answer: 0 Answer: 90 degree 417. If the torque induced is zero in the dc machine, 396. A synchronous generator is operating with a Ef = it can be said that 1.40 pu. This machine having Xs of 1.2 pu, is Answer: current is zero ------------------------------------------------PAGE 11-------------------------------------------------- EE COACH-3-2025 CERTC COMPLETE ENGINEERING REVIEW AND TRAINING CENTER Rm 5 01, G. K. Ch ua Bld g., M. J. Cu en co A ve. Ce bu Ci t y Contact No.0917-302-8824 COACHING NOTES 3 – EE PROFESSIONAL SUBJECTS 418. If the torque is in the direction of rotation, its excitation emf adjusted to 1.3 pv, the the DC machine acts as alternator delivers an output of 0.5 pv. The load Answer: motor angle is 419. The cogging torque is absent in the permanent Answer: 17.92 (δ = atan(0.5*0.8/1.3)) magnet dc machine is due to 443. Wound rotor induction motor is most appropriate Answer: non-magnetic nature of rotor for the applications requiring 420. The phasor addition of stator and rotor mmfs in Answer: variable starting torque a cylindrical rotor synchronous machine, is 444. When the poles of a 3-phase wound rotor induction possible because motor increased, it Answer: mmfs are stationary with respect to each Answer: will increase maximum power factor other 445. The magnetization current drawn from an AC supply 421. For the effective electromechanical energy a synchronous motor is used to conversion in the device, the developed torque Answer: set up flux in magnetic circuit of device depends upon 446. The armature current is ___ at unity power factor Answer: stator field and rotor field and the when compared to leading power factor for a motor. torque angle Answer: maximum 422. DC Motor torque depends on 447. The armature current is ___ at unity power factor Answer: both geometry and magnetic properties of than motor at lagging power factor. the structure Answer: mi

EE Coaching Notes 3 PDF: Electromagnetics & Electric Circuits

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