Question 1

A microphone converts sound waves into electrical signals using electromagnetic induction. Which of the following best describes the process by which a moving coil microphone generates an electrical signal?

Accepted Answer

A moving coil attached to a diaphragm vibrates in a stationary magnetic field, changing the magnetic flux and inducing an emf.

Question 2

Which equation correctly defines the magnetic flux $$\Phi$$ through a surface of area $$A in a $$uniform magnetic field $$B at an $$angle $$	heta to $$the normal of the surface?

Accepted Answer

$$\Phi = B A \cos 	heta$$

Question 3

A bar magnet is dropped through a copper loop. According to Lenz’s law, what happens to the magnet’s motion compared to free fall, and why?

Accepted Answer

It falls slower because the induced current creates a magnetic field opposing the motion.

Question 4

A wire loop of area $$A is $$placed in a uniform magnetic field $$B$$ such that the angle between the field and the normal to the loop is $$	heta. If $$the area of the loop is doubled while $$B$$ and $$	heta$$ remain constant, what happens to the magnetic flux through the loop?

Accepted Answer

It doubles.

Question 5

According to Faraday’s Law, which of the following actions will NOT induce an emf in a wire loop placed in a uniform magnetic field?

Accepted Answer

Moving the loop parallel to the field lines without changing its orientation or area.

Question 6

A solenoid has $$N$$ turns, length $$l$$, and cross-sectional area $$A. $$Its inductance is given by $$L = \mu_0$ N^2$ A / l. If $$both the number of turns and the length are doubled, by what factor does the inductance change?

Accepted Answer

It doubles.

Question 7

A generator coil rotates in a magnetic field. If the angular velocity $$\omega of $$the coil is doubled, what happens to the maximum induced emf ($$\$$varepsilon_0$$)?

Accepted Answer

It doubles.

Question 8

A transformer has a primary coil with 100 turns and a secondary coil with 400 turns. If the input voltage is 120 V AC, what is the output voltage (assuming ideal transformer)?

Accepted Answer

480 V

Question 9

A 6 V battery is connected to the primary coil of a transformer. What is the voltage across the secondary coil?

Accepted Answer

Zero

Question 10

A wire loop is being pulled through a region with a uniform magnetic field directed into the page. If the loop is entirely within the field and moves at constant velocity, what is the direction of the induced current?

Accepted Answer

No induced current

Question 11

A wire loop is being pulled out of a region with a uniform magnetic field directed into the page. What is the direction of the induced current as the loop exits the field?

Accepted Answer

Clockwise

Question 12

A coil is rotated in a magnetic field pointing to the left. As the coil rotates into the field, in what direction is the induced current?

Accepted Answer

Counterclockwise

Question 13

A wire loop is being pulled away from a long, straight current-carrying wire. What is the direction of the induced current in the loop?

Accepted Answer

Clockwise

Question 14

If the current in an RL circuit is doubled and the inductance is increased by a factor of 4, by what factor does the energy stored in the inductor increase?

Accepted Answer

Factor of 16

Question 15

Which of the following best explains why a magnet falling through a copper pipe slows down compared to free fall?

Accepted Answer

Eddy currents are induced in the pipe, creating a magnetic field that opposes the motion of the magnet.

Question 16

A coil with $$N$$ turns is placed in a time-varying magnetic field. According to Faraday’s Law, the induced emf is given by:

Accepted Answer

$$\varepsilon = -N \Delta \Phi / \Delta t$$

Question 17

A transformer is used to step down the voltage from 240 V to 120 V. If the current in the secondary coil is 2 A, what is the current in the primary coil (assuming an ideal transformer)?

Accepted Answer

1 A

Question 18

Which of the following statements about energy in electromagnetic induction is correct?

Accepted Answer

The energy for the induced current comes from the mechanical work done against the induced emf.

Question 19

A wire loop is shrinking in a uniform magnetic field pointing into the page. What is the direction of the induced current?

Accepted Answer

Clockwise

Magnetic Flux and Faraday’s Law of Induction – Study Notes

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