Q: A 10 H inductor carries a current of 2 A. What is the energy stored in the inductor?

$$ U = \frac{1}{2} L I^2$ = \frac{1}{2} \times 10 \times 2^2$ = 20 \; \text{J} $$

Q: After a long time, what is the current in the RL circuit described above?

$$ I = \frac{\mathcal{E}}{R} = \frac{120}{200} = 0.6\;\text{A} $$

Q: Which equation describes the growth of current in an RL circuit after the switch is closed at $$t=0$$?

$$ I(t) = \frac{\mathcal{E}}{R} \left(1 - e$$^{-t/\tau}$$\right) $$

Question 1

Which of the following best describes mutual inductance?

Accepted Answer

The ability of one coil to induce an emf in another coil when the current in the first coil changes.

Question 2

What is the SI unit of inductance?

Accepted Answer

Henry (H)

Question 3

A 10 H inductor carries a current of 2 A. What is the energy stored in the inductor?

Accepted Answer

$$ U = \frac{1}{2} L I^2$ = \frac{1}{2} 	imes 10 	imes 2^2$ = 20 \; 	ext{J} $$

Question 4

In an RL circuit, what is the time constant $$	au$$?

Accepted Answer

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

Question 5

Immediately after the switch is closed in an RL circuit with $$\mathcal{E} = 120\;	ext{V}$$, $$R = 200\;\Omega$$, and $$L = 10\;	ext{H}$$, what is the rate of change of current $$\frac{dI}{dt}$$?

Accepted Answer

$$ \frac{dI}{dt} = \frac{\mathcal{E}}{L} = \frac{120}{10} = 12\;	ext{A/s} $$

Question 6

After a long time, what is the current in the RL circuit described above?

Accepted Answer

$$ I = \frac{\mathcal{E}}{R} = \frac{120}{200} = 0.6\;	ext{A} $$

Question 7

Which equation describes the growth of current in an RL circuit after the switch is closed at $$t=0$$?

Accepted Answer

$$ I(t) = \frac{\mathcal{E}}{R} \left(1 - e$$^{-t/	au}$$ight) $$

Question 8

In an LC circuit, what happens to the energy stored in the capacitor and inductor over time?

Accepted Answer

The energy oscillates between the electric field of the capacitor and the magnetic field of the inductor.

Question 9

Which of the following best describes the function of an LC circuit in a radio tuner?

Accepted Answer

It filters out unwanted frequencies by resonance.

Question 10

If the mutual inductance between two coils is $$M$$ and the current in coil 1 changes at a rate $$\frac{dI_1$}{dt}$$, what is the induced emf in coil 2?

Accepted Answer

$$ \mathcal{E}_2 = -M \frac{dI_1$}{dt} $$

Question 11

A coil with self-inductance $$L$$ has a current $$I$$ increasing at a constant rate. What is the induced emf across the coil?

Accepted Answer

$$ \mathcal{E} = -L \frac{dI}{dt} $$

Question 12

Which of the following statements about the energy in an LC circuit is correct?

Accepted Answer

The total energy in the circuit remains constant, oscillating between the capacitor and the inductor.

Question 13

A real-world application of mutual inductance is:

Accepted Answer

A transformer in a power supply.

Question 14

If the inductance $$L of a $$coil is doubled while keeping the current $$I$$ constant, what happens to the energy stored in the inductor?

Accepted Answer

It doubles.

Question 15

Which of the following is true about the time constant $$	au in an RL $$circuit?

Accepted Answer

It is the time required for the current to reach about 63% of its final value.

Question 16

In a practical RL circuit, why does the current not immediately reach its maximum value when the switch is closed?

Accepted Answer

The inductor opposes changes in current due to self-inductance.

Question 17

Which of the following best describes the energy transfer in an LC circuit?

Accepted Answer

Energy oscillates between the electric field of the capacitor and the magnetic field of the inductor.

Question 18

A 5 H inductor is connected in series with a 100 Ω resistor and a 50 V battery. What is the time constant of the circuit?

Accepted Answer

$$ 	au = \frac{L}{R} = \frac{5}{100} = 0.05\;	ext{s} $$

Inductance and LC/RL Circuits: Concepts and Applications

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