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Questions and Answers

Which element is not suitable for analysis using Ohm’s Law?

  • Inductor
  • Transistor (correct)
  • Resistor
  • Capacitor

What remains constant inside a charged spherical shell?

  • Electrical potential (correct)
  • Magnetic field
  • Charge density
  • Electric field strength

Where does electrostatic shielding occur?

  • At the shell surface
  • Outside the shell
  • In the conductive material
  • Inside the spherical shell (correct)

How is the peak value in an AC circuit calculated?

<p>Using RMS value and peak factor (A)</p> Signup and view all the answers

Which statement regarding alternating current is true?

<p>AC always has a non-zero frequency (A)</p> Signup and view all the answers

How many cycles are completed in 2 seconds at a frequency of 100 Hz?

<p>200 cycles (B)</p> Signup and view all the answers

What is the direction of drift velocity in relation to the electric field?

<p>Opposite to the electric field (C)</p> Signup and view all the answers

In a series circuit where R1 > R2, which resistor consumes more power?

<p>R1 (A)</p> Signup and view all the answers

What is the correct equation for calculating power in a series circuit?

<p>$P = I^2 imes R$ (A)</p> Signup and view all the answers

Electrostatic shielding occurs inside a charged spherical shell where the electric field is present.

<p>False (B)</p> Signup and view all the answers

What is the peak value in an AC circuit when the RMS value is 50 and the peak factor is 1.414?

<p>70.7</p> Signup and view all the answers

The current density for a current of 30 A through an area of 0.5 m² is _______ A/m².

<p>60</p> Signup and view all the answers

Match the following AC circuit terms with their definitions:

<p>RMS Value = Root Mean Square value of the current Peak Factor = Ratio of peak value to RMS value Frequency = Number of cycles per second Cycle = One complete wave of alternating current</p> Signup and view all the answers

If the frequency of an AC signal is 50 Hz, how many cycles occur in 1 second?

<p>50 cycles (C)</p> Signup and view all the answers

The drift velocity of charge carriers is in the same direction as the electric field.

<p>False (B)</p> Signup and view all the answers

What is the electrical potential inside a charged spherical shell?

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

What is the electric field inside a spherical shell?

<p>Zero (C)</p> Signup and view all the answers

Electric potential is a vector quantity.

<p>False (B)</p> Signup and view all the answers

What do closely spaced lines of force in an electric field indicate?

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

The magnitude of the mutually induced emf in a transformer is directly proportional to the rate of change of ______ and the number of secondary turns.

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

Match each electric current definition with the correct description:

<p>Direct current = Flows in one direction Alternating current = Changes direction periodically Current density = Current per unit area Electrical conductivity = Ability to conduct electric current</p> Signup and view all the answers

What characterizes a direct current?

<p>Has a constant magnitude (C)</p> Signup and view all the answers

Andre-Marie Ampere first defined electric current.

<p>True (A)</p> Signup and view all the answers

How many electrons make up 2 Coulombs of electric charge?

<p>12.48 * 10^18 electrons</p> Signup and view all the answers

Electrical conductivity is the ratio of ______ density to the electric field.

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

What happens when the number of secondary turns in a transformer is less than the number of primary turns?

<p>Voltage is stepped down (B)</p> Signup and view all the answers

Hans Christian Orsted discovered that electric current can create a magnetic field.

<p>True (A)</p> Signup and view all the answers

What defines the average value in an AC circuit?

<p>RMS value/Form factor</p> Signup and view all the answers

What kind of quantity is electrical potential?

<p>Scalar quantity (D)</p> Signup and view all the answers

The frequency of direct current is ______.

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

What is responsible for electric current flow?

<p>Voltage difference</p> Signup and view all the answers

What is required for current to flow in a circuit?

<p>Electrons (C)</p> Signup and view all the answers

In accordance with Kirchhoff's Current Law, the current entering a junction is equal to the current leaving it.

<p>True (A)</p> Signup and view all the answers

How many directions can the electric field at a point have?

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

When the number of secondary turns is greater than the number of primary turns in a transformer, the voltage is stepped _____

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

What does the voltage transformation ratio in electrical engineering indicate?

<p>Ratio of induced emf in secondary to induced emf in primary (B), Ratio of secondary turns to primary turns (C)</p> Signup and view all the answers

The induced emf in an ideal transformer primary circuit remains unaffected when the secondary is open.

<p>False (B)</p> Signup and view all the answers

What does positive power in an electrical element indicate?

<p>Element is absorbing power</p> Signup and view all the answers

According to Lenz’s law, the induced emf will act to _____ the supply voltage.

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

Which type of circuit cannot be analyzed using Ohm’s Law?

<p>Unilateral (C)</p> Signup and view all the answers

According to Kirchhoff's Voltage Law, the algebraic sum of voltages in a closed loop is zero.

<p>True (A)</p> Signup and view all the answers

Match the following concepts in electrical engineering:

<p>KCL = Algebraic sum of currents must be zero at a junction KVL = Algebraic sum of voltages must be zero around a closed loop Induced emf = Opposes the cause that produced it Voltage transformation = Ratio of secondary turns to primary turns</p> Signup and view all the answers

What type of current does the primary circuit of an ideal transformer draw when the secondary is open?

<p>Magnetizing current (D)</p> Signup and view all the answers

What law provides a framework for the conservation of energy in a closed loop of a circuit?

<p>Kirchhoff's Voltage Law</p> Signup and view all the answers

The number of primary turns is equal to the ____ induced emf in primary per turn.

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

Ohm's law can be used to analyze all types of circuits without exception.

<p>False (B)</p> Signup and view all the answers

Flashcards

Why is Ohm's Law not applicable to transistors?

Ohm's Law is not applicable to transistors because they form unilateral networks, where current only flows in one direction. This means the relationship between voltage, current, and resistance defined by Ohm's Law doesn't hold true for transistors.

What is constant inside a charged spherical shell?

The electric potential inside a charged spherical shell is constant and can be calculated using the formula: V = kq/R, where V is the potential, k is Coulomb's constant, q is the charge, and R is the radius of the shell.

Where does electrostatic shielding occur?

Electrostatic shielding occurs inside a charged spherical shell because the electric field inside the shell is zero. This means that any charges placed inside the shell will not experience any electric force.

How to calculate peak value in an AC circuit?

The peak value of an AC circuit is calculated by multiplying the RMS value by the peak factor. The peak factor is a constant value that depends on the waveform of the AC signal.

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Which statement about alternating current (AC) is incorrect?

Alternating current (AC) always has a non-zero frequency. This means that the current is constantly changing direction.

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How many cycles are there in 2 seconds for a 100 Hz frequency?

The number of cycles in an AC signal for a specific time is calculated by multiplying the frequency of the signal by the time period. So, for a frequency of 100 Hz and a time period of 2 seconds, the number of cycles would be 200.

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What is the direction of drift velocity in relation to the electric field?

Drift velocity refers to the average velocity of charge carriers in a material under the influence of an electric field. The direction of drift velocity is always opposite to the direction of the electric field.

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What is the current density for a current of 30A through an area of 0.5m²?

Current density (J) is a vector quantity that represents the amount of current flowing per unit area. It is calculated by dividing the current (I) by the cross-sectional area (A) through which the current is flowing. So, for a current of 30A through an area of 0.5m², the current density would be 60 A/m².

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Why doesn't Ohm's Law apply to transistors?

Ohm's Law does not apply to unilateral networks, which only allow current flow in one direction. Transistors are examples of such networks, hence Ohm's Law does not apply to them.

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How do you calculate the peak value in an AC circuit?

The peak value of an alternating current (AC) circuit is calculated by multiplying the root mean square (RMS) value of the current by the peak factor. The peak factor is a constant value that depends on the waveform of the AC signal.

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Is the frequency of AC zero?

The frequency of an alternating current (AC) is never zero. AC signals always have a non-zero frequency, meaning the current direction changes periodically.

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What is current density?

Current density represents the amount of current flowing per unit area. It is a vector quantity and is calculated by dividing the current (I) by the cross-sectional area (A) through which the current is flowing. The formula is: J = I/A.

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Proton

A positively charged particle found in the nucleus of an atom.

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Electron

A negatively charged particle that orbits the nucleus of an atom.

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Nucleus

The central core of an atom, containing protons and neutrons.

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Electric Current

The flow of electrons through a circuit.

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Voltage

The difference in electrical potential between two points in a circuit.

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Resistance

A measure of a material's resistance to the flow of electrical current.

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Ohm's Law

A law that describes the relationship between voltage, current, and resistance in a circuit.

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Electric Motor

A device that converts electrical energy into mechanical energy.

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Generator

A device that converts mechanical energy into electrical energy.

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Circuit

A closed loop that allows electrical current to flow.

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Capacitor

A device that stores electrical energy.

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Inductor

A device that restricts the flow of electrical current.

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Rectifier

A device that converts alternating current (AC) to direct current (DC).

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Inverter

A device that converts direct current (DC) to alternating current (AC).

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Electric Field

The force per unit charge experienced by a charge in an electric field.

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What is electric potential?

The work done in moving a unit positive charge from infinity to a point in the electric field is called electric potential. It is a scalar quantity, denoted by the symbol V.

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Why is the electric field inside a spherical shell zero?

The electric field inside a uniformly charged spherical shell is always zero, regardless of the charge distribution on the shell.

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What is the electric field outside a charged spherical shell?

The electric field outside a uniformly charged spherical shell is the same as that of a point charge located at the center of the shell, with a charge equal to the total charge on the shell.

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Is electric potential a scalar or vector quantity?

Electric potential is a scalar quantity, which means it only has magnitude and not direction.

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What do crowded lines of force indicate?

Crowded lines of force in an electric field indicate a strong electric field. This means that the force exerted on a charge placed in that region would be strong.

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What is the direction of the electric field at a point?

The direction of the electric field at a point is along the line tangent to the electric field line at that point.

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What is the relationship between mutually induced emf, rate of change of flux, and secondary turns in a transformer?

The magnitude of the mutual induced electromotive force (emf) E2 in a transformer is directly proportional to the rate of change of flux and the number of secondary turns.

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What happens to the voltage in a transformer if the number of secondary turns is less than the primary turns?

In a transformer, when the number of secondary turns is less than the number of primary turns, the voltage gets stepped down.

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How to calculate the number of primary turns in a transformer?

The number of primary turns in a transformer can be calculated by dividing the primary voltage by the emf per turn.

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How is the average value of an AC circuit related to the RMS value?

The average value of an AC circuit is equal to the RMS value divided by the form factor. The form factor is a constant that depends on the waveform of the AC signal.

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Who defined electric current and devised a method to measure it?

Andre-Marie Ampere defined electric current and devised a method to measure current in the 1820s.

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How many electrons constitute 2 Coulombs of electric charge?

For 2 Coulombs of electric charge, there are 12.48 * 1018 electrons. This is because a single Coulomb of charge contains 6.24 x 1018 electrons.

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What are the main characteristics of direct current?

Direct current (DC) flows in one direction and has a constant magnitude and zero frequency.

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Who first witnessed the effect of magnetism?

Hans Christian Orsted was the first to witness the effect of magnetism, discovering that electric current can create a magnetic field.

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What is the relationship between electrical conductivity, current density, and electric field?

Electrical conductivity (σ) is the ratio of current density (J) to the electric field (E). It measures a material's ability to conduct electric current.

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Study Notes

Ohm's Law and its Limitations

  • Ohm's Law does not apply to transistors due to their unilateral nature. Transistors form networks where current flow depends on more than simply resistance and voltage.
  • Ohm's Law is not applicable to unilateral networks, such as transistors; these networks only allow current flow in one direction.

Charged Spherical Shells

  • The electrical potential within a uniformly charged spherical shell is constant.
  • The formula for this constant potential is: V = kq/R, where k is a constant, q is the charge, and R is the radius.
  • The electric field inside a charged spherical shell is zero.

Electrostatic Shielding

  • Electrostatic shielding occurs inside a spherical shell, creating a zone where the electric field is zero.

Alternating Current (AC) Circuits

  • Peak Value Calculation: Peak value = RMS value × Peak factor.
  • Frequency and Cycles: Frequency × Time = Number of cycles. A 100 Hz AC signal completes 200 cycles in 2 seconds.
  • Inaccurate AC Statement: The frequency of an alternating current is always non-zero. A zero frequency indicates direct current (DC).
  • Average Value: Average value = RMS value / Form factor

Drift Velocity

  • Drift velocity is always opposite to the direction of the electric field.

Current Density

  • Current density (J) is calculated as current (I) divided by area (A): J = I/A. For a 30 A current through 0.5 m² area, the current density is 60 A/m².

Power in Series Circuits

  • In a series circuit, the resistor with the higher resistance will dissipate more power. This is because the current is the same for all components in series, and power is proportional to both current squared and resistance.

Transformer Basics

  • Voltage Transformation: The voltage transformation ratio is the ratio of secondary turns to primary turns, i.e., Vsecondary / Vprimary = Nsecondary / Nprimary .
  • Step-up/Step-down: A transformer with more secondary turns than primary turns steps up the voltage. Conversely, a transformer with fewer secondary turns steps down the voltage.
  • Induced EMF: Induced emf in the primary is the product of primary turns and the emf induced per turn.

Kirchhoff's Laws

  • Kirchhoff's Current Law (KCL): The algebraic sum of currents entering and leaving a junction is zero.
  • Kirchhoff's Voltage Law (KVL): The algebraic sum of voltages around a closed loop is zero.

Additional Concepts

  • Electric Field Direction: The direction of the electric field is tangent to the electric field line.
  • Electric Potential: Electric potential is a scalar quantity.
  • Electric Field Strength: Crowded electric field lines indicate a strong electric field.
  • Electrical Conductivity: Electrical conductivity (σ) is the ratio of current density (J) to electric field (E). σ = J / E
  • Current Carriers: Current is carried by electrons.
  • Power in an Element: Positive power indicates the element is absorbing power.
  • Ideal Transformer Magnetizing Current: When the secondary of an ideal transformer is open, the primary circuit draws magnetizing current.
  • DC Characteristics: Direct current (DC) has a magnitude that is constant over time and a frequency of zero. DC can be transmitted over longer distances with reduced power loss.

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Description

This quiz covers essential concepts in electromagnetism, focusing on Ohm's Law, charged spherical shells, electrostatic shielding, and alternating current circuits. Test your understanding of formulas and physical principles related to these topics to reinforce your knowledge. Ideal for students studying physics or engineering.

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