Q: Which equation correctly expresses the magnetic flux $$\Phi_B$$ through a surface of area $$A in a $$uniform magnetic field $$B at an $$angle $$\theta to $$the normal?

$$\Phi_B = B \cos \theta \cdot A$$

Question 1

A stationary magnet is placed near a coil connected to a galvanometer. Which of the following will induce a current in the coil?

Accepted Answer

Moving the magnet away from the coil

Question 2

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

Accepted Answer

$$\Phi_B = B \cos 	heta \cdot A$$

Question 3

According to Faraday's Law, what determines the magnitude of the induced emf in a coil?

Accepted Answer

The rate of change of magnetic flux through the coil

Question 4

A rectangular loop of wire is rotated in a uniform magnetic field. What is the primary reason an emf is induced in the loop?

Accepted Answer

The angle between the magnetic field and the loop changes, altering the magnetic flux

Question 5

Which statement best describes Lenz's Law?

Accepted Answer

The induced current opposes the change in magnetic flux that produced it

Question 6

A metal rod of length $$l$$ moves at velocity $$v$$ perpendicular to a uniform magnetic field $$B. $$What is the motional emf induced across the ends of the rod?

Accepted Answer

$$\varepsilon = B l v$$

Question 7

Eddy currents are responsible for which of the following real-world phenomena?

Accepted Answer

The operation of a metal detector

Question 8

In a transformer, the primary coil has $$N_1$$ turns and the secondary coil has $$N_2$$ turns. If the input voltage is $$V_1$$, what is the output voltage $$V_2$$?

Accepted Answer

$$V_2$$ = $$V_1$$ \cdot \frac{$$N_2$$}{$$N_1$$}$$

Question 9

Which of the following best describes mutual inductance?

Accepted Answer

A changing current in one coil induces an emf in a nearby coil

Question 10

A Tesla coil uses mutual induction to generate high voltages. If the primary coil has 100 turns and the secondary coil has 10,000 turns, and the input voltage is 120 V, what is the output voltage (neglecting losses)?

Accepted Answer

$$V_2 = 12$$,000\ 	ext{V}$$

Question 11

Which equation gives the energy stored in an inductor with inductance $$L$$ carrying current $$I$$?

Accepted Answer

$$U = \frac{1}{2} L I^2$

Question 12

In an R-L circuit, the current as a function of time after closing the switch is given by:

Accepted Answer

$$I(t) = \frac{\varepsilon}{R} \left(1 - e$$^{-\frac{R}$${L} t}\right)$$

Question 13

Which of the following is a practical application of an L-C circuit?

Accepted Answer

Tuning a radio to a specific frequency

Question 14

A coil with $$N$$ turns and area $$A is $$placed in a uniform magnetic field $$B. If $$the field changes from $$B_1 to$$ $$B_2 in $$time $$\Delta t$$, what is the average induced emf?

Accepted Answer

$$\varepsilon = N \frac{(B_2$ - B_1$) A}{\Delta t}$$

Question 15

Which of the following actions will NOT induce a current in a coil?

Accepted Answer

Moving a magnet parallel to the axis of the coil without changing its distance

Question 16

A metal disk rotates in a magnetic field, generating eddy currents. What is the effect of these currents on the disk's motion?

Accepted Answer

They create a force that opposes the disk's rotation, causing it to slow down

Question 17

In a transformer, why are the cores often laminated?

Accepted Answer

To reduce energy losses due to eddy currents

Question 18

Which of the following best describes self-inductance?

Accepted Answer

A changing current in a coil induces an emf in the same coil

Question 19

A coil with inductance $$L is $$connected in series with a resistor $$R$$ and a battery of emf $$\varepsilon. $$What is the time constant $$	au$$ for the current to reach approximately 63% of its final value?

Accepted Answer

$$	au = \frac{L}{R}$$

Electromagnetic Induction (Chapter 21) – College Physics Study Notes

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