Question 1

A rectangular loop of wire with area $$A = 0.04\ \mathrm{m}^2 is $$placed in a uniform magnetic field $$B = 0.3\ \mathrm{T}$$ such that the normal to the loop makes an angle of $$60^\circ$$ with the field. What is the magnetic flux through the loop?

Accepted Answer

$$0.006\ \mathrm{Wb}$$

Question 2

A circular coil with $$N = 100$$ turns and radius $$r = 10\ \mathrm{cm} is $$placed perpendicular to a uniform magnetic field. If the field decreases uniformly from $$0.5\ \mathrm{T} to$$ $$0 in$$ $$0.2\ \mathrm{s}$$, what is the magnitude of the induced emf?

Accepted Answer

$$0.79\ \mathrm{V}$$

Question 3

According to Lenz's Law, if the magnetic flux through a loop is increasing downward, what is the direction of the induced current as viewed from above?

Accepted Answer

Counterclockwise

Question 4

A square loop lies in the plane of the page. A decreasing magnetic field is directed into the page. What is the direction of the induced current?

Accepted Answer

Counterclockwise

Question 5

A straight wire carries a steady current $$I. A $$rectangular loop lies in the same plane as the wire and is pushed toward the wire. What is the direction of the induced current in the loop?

Accepted Answer

Clockwise

Question 6

A transformer has $$N_p = 500$$ turns on the primary coil and $$N_s = 100$$ turns on the secondary coil. If the input voltage is $$120\ \mathrm{V}$$, what is the output voltage?

Accepted Answer

$$24\ \mathrm{V}$$

Question 7

Which of the following changes will NOT induce an emf in a loop of wire?

Accepted Answer

Keeping the magnetic field, area, and orientation constant

Question 8

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

Accepted Answer

$$vBL$$

Question 9

The energy stored in an inductor with inductance $$L$$ carrying current $$I is $$given by:

Accepted Answer

$$U = \frac{1}{2}LI^2$

Question 10

If the number of turns in both coils of a transformer is doubled (with all other parameters unchanged), how does the mutual inductance $$M$$ change?

Accepted Answer

It quadruples

Question 11

In an RL circuit, the time constant $$	au is $$given by:

Accepted Answer

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

Question 12

A generator coil with $$N$$ turns, area $$A$$, rotates with angular speed $$\omega in a $$uniform magnetic field $$B. $$What is the maximum emf generated?

Accepted Answer

$$NBA\omega$$

Question 13

A long solenoid has $$n$$ turns per unit length, cross-sectional area $$A$$, and carries current $$I. $$What is the self-inductance $$L of $$the solenoid?

Accepted Answer

$$L = \mu_0$ n^2$ l A$$

Question 14

In a step-down transformer, which of the following is true about the current in the secondary coil compared to the primary coil (assuming ideal transformer and same power)?

Accepted Answer

The secondary current is greater than the primary current

Question 15

A circuit contains a resistor $$R$$ and an inductor $$L in $$series with a battery of emf $$\mathcal{E}. $$Immediately after the switch is closed, what is the current through the inductor?

Accepted Answer

Zero

Question 16

Which of the following best describes the energy density stored in the magnetic field of a solenoid?

Accepted Answer

$$u = \frac{B^2$}{2\mu_0$}$$

Question 17

A circuit with a resistor and an uncharged capacitor is placed in a region where the magnetic field is increasing into the page. Which plate of the capacitor becomes positively charged?

Accepted Answer

Top plate

Question 18

Which of the following is a correct statement of Faraday's Law for a coil with $$N$$ turns?

Accepted Answer

$$\mathcal{E} = -N \frac{\Delta \Phi}{\Delta t}$$

Question 19

A motional emf is generated when a conductor of length $$L$$ moves with velocity $$v$$ perpendicular to a magnetic field $$B. $$Which equation correctly relates the electric field $$E$$ inside the conductor to the magnetic field and velocity?

Accepted Answer

$$E = vB$$

Question 20

Which of the following best describes the effect of self-inductance in a circuit?

Accepted Answer

It opposes changes in the current

Electromagnetic Induction: Principles, Laws, and Applications

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