Electromagnetism Concepts Quiz

<p>a high resistance in series with galvanometer.</p> Signup and view all the answers

<p>north-south</p> Signup and view all the answers

<p>LI²</p> Signup and view all the answers

<p>changing electric field</p> Signup and view all the answers

<p>a virtual enlarged image</p> Signup and view all the answers

<p>Io cos² θ</p> Signup and view all the answers

<p>thermionic emission</p> Signup and view all the answers

<p>most of the region in an atom is empty space</p> Signup and view all the answers

<p>isotopes</p> Signup and view all the answers

<p>conductors = Eg &lt; 3 eV insulators = Eg = 0 eV semiconductors = Eg &gt; 3 eV</p> Signup and view all the answers

<p>polar</p> Signup and view all the answers

<p>zero</p> Signup and view all the answers

<p>phasor</p> Signup and view all the answers

<p>phase</p> Signup and view all the answers

<p>photon</p> Signup and view all the answers

<p>Gauss's law in electrostatics states that the total electric flux through any closed surface is proportional to the enclosed electric charge. This flux is defined as the surface integral of the electric field over the closed surface. <strong>ΦE = ∑Qi / ε0</strong> Where ΦE is the electric flux, Qi is the enclosed charge, and ε0 is the permittivity of free space. Gauss's law implies that the electric field is stronger near a higher charge concentration and that electric field lines originate from positive charges and terminate on negative charges.</p> Signup and view all the answers

<p>Drift velocity refers to the average velocity attained by free electrons in a conductor when an electric field is applied. It is a constant average velocity that the electrons achieve while moving randomly due to collisions with atoms in the conductor. The direction of the drift velocity is opposite to the direction of the electric field. Mobility (µ) of free electrons is a measure of their ability to move in an electric field. It is defined as the drift velocity per unit electric field: µ = vd / E. Higher mobility implies that electrons can move freely in the conductor and experience less resistance to their motion.</p> Signup and view all the answers

<p>The magnetic field at the midpoint of a long solenoid can be calculated using the following formula: B = µ0nI where, B is the magnetic field strength, µ0 is the permeability of free space (4π × 10⁻⁷ T m/A), n is the number of turns per unit length (1000 turns/m in this case), I is the current through the solenoid (2 A). Therefore, B = (4π × 10⁻⁷ T m/A) × (1000 turns/m) × (2 A) = 8π × 10⁻⁴ T or approximately 2.51 × 10⁻³ T.</p> Signup and view all the answers

<p>The principle of an AC generator is based on Faraday's law of electromagnetic induction. When a coil rotates in a magnetic field, the magnetic flux through the coil changes with time, inducing an electromotive force (EMF) in the coil. This EMF is then an alternating current as it changes direction periodically with the rotation of the coil. As the coil rotates, the magnetic flux linked with it changes continuously. This changing flux induces an EMF in the coil according to Faraday's law. The induced EMF is alternating because the magnetic flux changes sinusoidally as the coil rotates. This changing EMF causes the current to flow back and forth through the coil, resulting in alternating current (AC).</p> Signup and view all the answers

<p>Ultraviolet (UV) radiation has various applications, including:</p> <ol> <li>Sterilization: UV radiation can be used to sterilize surfaces, medical equipment, and water supplies. It damages the DNA of microorganisms, killing them effectively.</li> <li>Medical treatment: UV radiation is used in phototherapy to treat certain skin conditions like psoriasis and vitiligo. It also serves as a treatment for seasonal affective disorder (SAD).</li> </ol> Signup and view all the answers

<p>a) The objective lens used in a refracting telescope is a convex lens. b) The objective mirror used in a reflecting telescope is a concave mirror.</p> Signup and view all the answers

<p>Total internal reflection occurs when a light ray travels from a denser medium to a rarer medium (for example, from water to air) and the angle of incidence is greater than the critical angle. Here are the two conditions:</p> <ol> <li>The light ray must travel from a denser medium to a rarer medium. The refractive index of the denser medium must be greater than that of the rarer medium.</li> <li>The angle of incidence must be greater than the critical angle, which is the angle of incidence at which the refracted ray grazes along the interface between the two media.</li> </ol> Signup and view all the answers

<p>In an n-type semiconductor, the majority charge carriers are electrons, and the minority charge carriers are holes. This type of semiconductor is achieved by doping a pure semiconductor (like silicon) with a pentavalent element (like arsenic) which has five valence electrons. These extra electrons become free electrons, increasing the electron concentration and making it the majority carrier.</p> Signup and view all the answers

<p>Here are three important properties of electric field lines:</p> <ol> <li>Electric field lines always originate from positive charges and terminate at negative charges. They never start or end in mid-air.</li> <li>Electric field lines never intersect each other. If they did intersect, it would mean that the electric field has two different directions at the point of intersection, which is impossible.</li> <li>The density of electric field lines indicates the strength of the electric field. A region with a higher density of field lines corresponds to a stronger electric field.</li> </ol> Signup and view all the answers

<p>When two capacitors are connected in parallel, the effective capacitance (Ceq) is given by the sum of their individual capacitances (C1 and C2). This is because the voltage across both capacitors is the same, and the total charge stored is the sum of the charges stored on each capacitor. Ceq = C1 + C2</p> Signup and view all the answers

<p>The Lorentz force is the force experienced by a charged particle moving in a magnetic field. It is given by: F = q(v × B) Where: F is the Lorentz force vector q is the charge of the particle v is the velocity vector of the particle B is the magnetic field vector The cross product (×) indicates that the direction of the force is perpendicular to both the velocity vector and the magnetic field vector.</p> Signup and view all the answers

<p>Diamagnetic and paramagnetic materials are classified based on their response to an external magnetic field:</p> <ol> <li>Diamagnetic materials are weakly repelled by an external magnetic field. This is because the magnetic dipole moments of atoms in diamagnetic materials are induced by the external magnetic field and are aligned opposite to the field direction, leading to a weak repulsion.</li> <li>Paramagnetic materials are weakly attracted by an external magnetic field. This is because the magnetic dipole moments of atoms in paramagnetic materials are aligned with the external magnetic field, leading to a weak attraction.</li> <li>Diamagnetism is a universal phenomenon, present in all materials. However, it is often overshadowed by paramagnetism or ferromagnetism in materials that exhibit stronger magnetic properties.</li> <li>Diamagnetic materials have negative magnetic susceptibility, while paramagnetic materials have positive magnetic susceptibility.</li> </ol> Signup and view all the answers

<p>An experiment to demonstrate electromagnetic induction using a bar magnet and a coil can be conducted as follows:</p> <ol> <li>Set up: Place a coil of wire connected to a galvanometer on a horizontal surface. A bar magnet is held near the coil.</li> <li>Induction: Move the bar magnet towards the coil. As the magnet approaches the coil, the magnetic flux through the coil changes, inducing an electromotive force (EMF), which in turn causes a current to flow through the coil. This current will be detected by a needle deflection on the galvanometer.</li> <li>Observation: The needle of the galvanometer will deflect when the magnet is moving towards the coil. The direction of the deflection will depend on the direction of the magnet's movement relative to the coil and its north or south pole.</li> <li>Experiment: Repeat the process by moving the magnet away from the coil. The galvanometer will show a deflection in the opposite direction.</li> <li>Conclusion: The experiment demonstrates that a changing magnetic flux through a coil induces an EMF and current in the coil, a phenomenon known as electromagnetic induction.</li> </ol> Signup and view all the answers

<p>The photoelectric effect is the emission of electrons from a metal surface when light of suitable frequency falls on it. Here are three important experimental results:</p> <ol> <li>Threshold Frequency: The photoelectric effect only occurs when the incident light's frequency is above a certain minimum value called the threshold frequency. This frequency is specific to the material of the metal surface.</li> <li>Instantaneous Emission: Electron emission occurs instantaneously, as soon as the light of sufficient frequency falls on the surface. This suggests that the electrons absorb energy from the light in discrete packets called photons.</li> <li>Kinetic Energy: The kinetic energy of the emitted electrons is directly proportional to the frequency of the incident light. The kinetic energy of the emitted electrons is given by KE = hf - W where h is Planck's constant, f is the frequency of the incident light, and W is the work function representing the minimum energy required to eject an electron from the metal surface.</li> </ol> Signup and view all the answers

<p>Bohr's atomic model proposed a quantized structure for the hydrogen atom, revolutionizing our understanding of atomic structure. Its key postulates are:</p> <ol> <li>Quantized Electron Orbits: Electrons in atoms occupy specific circular orbits around the nucleus where they are allowed to exist without emitting energy. These allowed orbits, called stationary states, are characterized by specific values of energy, angular momentum, and radius.</li> <li>Energy Emission and Absorption: An electron can only transition from a stationary state to another by absorbing or emitting a photon of light. When an electron jumps from a higher energy level to a lower energy level, it emits a photon with energy equal to the difference in energy between the two levels. Conversely, an electron absorbs a photon with energy matching the energy difference to jump from a lower energy level to a higher one.</li> <li>Quantization of Angular Momentum: The angular momentum of an electron in a stationary orbit is quantized, meaning it can only take on specific discrete values. This is described by the equation: L = nh/2π, where L is the angular momentum, n is a positive integer (representing the principal quantum number), and h is Planck's constant.</li> </ol> Signup and view all the answers

<p>The energy equivalent of one atomic mass unit (1u) can be calculated using Einstein's famous mass-energy equivalence equation, E = mc²: Where: E is the energy equivalent of the mass m is the mass (in kg) c is the speed of light (3 x 10⁸ m/s) E = (1.6605 × 10⁻²⁷ kg) × (2.9979 × 10⁸ m/s)² ≈ 1.4924 × 10⁻¹⁰ J To convert the energy from joules to MeV (mega-electron volts), we use the conversion factor: 1 MeV = 1.602 × 10⁻¹³ J Therefore, E ≈ (1.4924 × 10⁻¹⁰ J) / (1.602 × 10⁻¹³ J/MeV) ≈ 931.5 MeV</p> Signup and view all the answers

<p>Consider an electric dipole consisting of two equal and opposite charges (+q and -q) separated by a distance 2a. We want to find the electric field at a point P on the axis of the dipole, at a distance r from the center of the dipole. Using Coulomb's law to find the electric field due to each charge separately:</p> <ul> <li>Electric field due to +q: E1 = (kq)/(r-a)² directed away from +q</li> <li>Electric field due to -q: E2 = (kq)/(r+a)² directed towards -q The net electric field at point P is the vector sum of E1 and E2. Since both fields are along the same direction (axis), we can add them algebraically. Therefore, E = E1 + E2 = (kq)/(r-a)² + (kq)/(r+a)² After simplification, we get the expression for the electric field on the axis of a dipole: E = (2kqa)/(r²-a²)²</li> </ul> Signup and view all the answers

<p>Let two cells with emfs E1, E2 and internal resistances r1, r2 be connected in series. The effective emf (E) of the combination is the sum of the individual emfs, and the effective internal resistance (r) is the sum of individual resistances, since the current flows through both cells in series:</p> <ul> <li>Effective emf (E) = E1 + E2</li> <li>Effective internal resistance (r) = r1 + r2</li> </ul> Signup and view all the answers