Question 1

In figure E19.12a, two light bulbs are connected in a loop that surrounds a solenoid connected to a source of AC current. In this case, both bulbs glow brightly. Now suppose that we connect various points in this circuit with a thick (low-resistance) copper wire, as shown in figures E19.12b through E19.12d. Which bulbs glow in each case?
-C.

A) Bulb $A$ glows but bulb $B$ goes out.
B) Bulb B glows but bulb $A$ goes out.
C) Both bulbs continue to glow.
D) Both bulbs go out.
E) One needs more information to answer.

Accepted Answer

The answer of In figure E19.12a, two light bulbs are...

Question 2

In figure E19.12a, two light bulbs are connected in a loop that surrounds a solenoid connected to a source of AC current. In this case, both bulbs glow brightly. Now suppose that we connect various points in this circuit with a thick (low-resistance) copper wire, as shown in figures E19.12b through E19.12d. Which bulbs glow in each case?
- Sunlight is absorbed by a black hat.
A) Consistent
B) Inconsistent

Accepted Answer

The answer of In figure E19.12a, two light bulbs are...

Question 3

Consider the two inductors shown below (which are in independent circuits). The induced emf in each inductor is such that the inductor behaves like a battery with its positive end to the right.
 
-(a) Which inductor carries the larger current?
A) Inductor 1
B) Inductor 2
C) The current or change in current is the same in both.
D) One needs more information to answer the question.

Accepted Answer

To determine which inductor carries a larger current, information such as the applied voltage, resistance in the circuit, and the inductance values of the inductors is required. Without such details, it's impossible to accurately answer the question.

Question 4

Consider the two inductors shown below (which are in independent circuits). The induced emf in each inductor is such that the inductor behaves like a battery with its positive end to the right.
 
-(b) In which is the current changing more rapidly?
A) Inductor 1
B) Inductor 2
C) The current or change in current is the same in both.
D) One needs more information to answer the question.

Accepted Answer

The answer of Consider the two inductors shown below (which...

Question 5

In the inductors shown in problem E20T.1, the current shown flowing through each coil must be

A) increasing.
B) decreasing.
C) remaining constant.
D) One needs more information to say how it is varying.

Accepted Answer

The answer of In the inductors shown in problem E20T.1,...

Question 6

Suppose we wrap a solenoid coil around a hollow cardboard cylinder. Now suppose that we insert an iron core into the solenoid. What will happen to the coil's inductance when we insert the iron core? (Explain.)
A) The inductance increases.
B) The inductance decreases.
C) The inductance is unchanged.
D) One needs more information to answer the question.

Accepted Answer

The inductance of a coil increases when an iron core is inserted because the iron core enhances the magnetic field inside the coil. This is due to the high permeability of iron compared to air or vacuum, which allows it to concentrate magnetic lines of force and thus increase the magnetic flux linkage for the same current, leading to higher inductance.

Question 7

Suppose we have a certain length of wire that we would like to wind around a cylindrical form in a single layer of closely spaced turns to make it more compact, and we would like to minimize the inductance of the resulting coil. All the available forms have a small enough radius that the length of the coil will be much larger than its radius. Given this, we should choose the form with
A) The smallest radius.
B) The largest radius.
C) Any radius (the inductance will be the same).
D) One needs more information to answer the question.

Accepted Answer

The answer of Suppose we have a certain length of...

Question 8

A coil with a self-inductance of $1 \mathrm{H}$ is connected in parallel to a $10-\Omega$ light bulb and a $5-\mathrm{V}$ battery. Very roughly how long would it keep the light bulb lit if the battery was disconnected from the circuit? (Choose the closest answer.)
A) $100 \mathrm{~s}$
B) $20 \mathrm{~s}$
C) $2 \mathrm{~s}$
D) $\mathbf{0 . 2 \mathrm { s }}$
E) $0.02 \mathrm{~s}$

Accepted Answer

The energy stored in the inductor can be calculated using the formula $E = \frac{1}{2}LI^2$, where $L$ is the inductance and $I$ is the current. When the battery is disconnected, this energy will dissipate through the light bulb at a rate given by $P = I^2R$, where $P$ is the power and $R$ is the resistance of the bulb. The time $t$ for the energy to dissipate can be estimated by $t = \frac{E}{P}$. Given the values, the time will be relatively short, making 0.2 s the closest estimate without performing detailed calculations.

Question 9

If we increase the resistance in the LR circuit shown in figure E20.1b, how would this change the rate of decay of the current through the coil?

A) The current will decay more quickly.}
B) The current will decay more slowly.
C) There will be no change in the rate of decay.
D) One needs more information to answer the question.

Accepted Answer

The answer of If we increase the resistance in the...

Question 10

The inductor in an LR circuit (see figure E20.1b) initially carries a current $I_{0}$ and therefore contains a certain amount of energy in its magnetic field. By the time that the current has decayed to half its initial value, what fraction of the inductor's magnetic field energy has been converted to thermal energy in the circuit's resistor?

A) $7 / 8$
B) $3 / 4$
C) $1 / 2$
D) $1 / 4$
E) $1 / 8$
F) Some other fraction (specify).

Accepted Answer

The answer of The inductor in an LR circuit (see...

Question 11

In an LC circuit, if we increase the capacitor's capacitance (while keeping everything else the same), the circuit's oscillation frequency will
A) increase.
B) decrease.
C) remain the same.
D) One needs more information to answer.

Accepted Answer

The oscillation frequency of an LC circuit is given by $f = \frac{1}{2\pi\sqrt{LC}}$, where $L$ is the inductance and $C$ is the capacitance. Increasing the capacitance ($C$) will increase the denominator, thus decreasing the frequency ($f$).

Question 12

In an LC circuit, if we increase the initial charge on the capacitor (while keeping everything else the same), the circuit's oscillation frequency will
A) increase.
B) decrease.
C) remain the same.
D) One needs more information to answer.

Accepted Answer

The oscillation frequency of an LC circuit is determined by the inductance (L) and capacitance (C) values, according to the formula $f = \frac{1}{2\pi\sqrt{LC}}$. It does not depend on the initial charge on the capacitor.

Question 13

A certain utility transformer is designed to step up the emf from $1 \mathrm{kV}$ to $25 \mathrm{kV}$. If the primary has 1000 turns of wire, how many turns of wire does the secondary have?
A) 25,000
B) 4000
C) 2500
D) 40
E) 25
F) Some other result (specify).
$\mathrm{T}$. One needs more information to answer.

Accepted Answer

The turns ratio of a transformer is equal to the ratio of the secondary voltage to the primary voltage. In this case, the secondary voltage is 25 kV and the primary voltage is 1 kV, so the turns ratio is 25. This means that the secondary winding has 25 times as many turns as the primary winding. Since the primary winding has 1000 turns, the secondary winding must have 25 * 1000 = 25,000 turns.

Quiz 4: Electricity and Magnetism Are Unified

Consider the two inductors shown below (which are in independent circuits) . The induced emf in each inductor is such that the inductor behaves like a battery with its positive end to the right. -(a) Which inductor carries the larger current?

Consider the two inductors shown below (which are in independent circuits) . The induced emf in each inductor is such that the inductor behaves like a battery with its positive end to the right. -(b) In which is the current changing more rapidly?

In the inductors shown in problem E20T.1, the current shown flowing through each coil must be

Suppose we wrap a solenoid coil around a hollow cardboard cylinder. Now suppose that we insert an iron core into the solenoid. What will happen to the coil's inductance when we insert the iron core? (Explain.)

A coil with a self-inductance of $1 \mathrm{H}$ is connected in parallel to a $10-\Omega$ light bulb and a $5-\mathrm{V}$ battery. Very roughly how long would it keep the light bulb lit if the battery was disconnected from the circuit? (Choose the closest answer.)

If we increase the resistance in the LR circuit shown in figure E20.1b, how would this change the rate of decay of the current through the coil?

In an LC circuit, if we increase the capacitor's capacitance (while keeping everything else the same) , the circuit's oscillation frequency will

In an LC circuit, if we increase the initial charge on the capacitor (while keeping everything else the same) , the circuit's oscillation frequency will

A certain utility transformer is designed to step up the emf from $1 \mathrm{kV}$ to $25 \mathrm{kV}$ . If the primary has 1000 turns of wire, how many turns of wire does the secondary have?

Quiz 4: Electricity and Magnetism Are Unified

Consider the two inductors shown below (which are in independent circuits) . The induced emf in each inductor is such that the inductor behaves like a battery with its positive end to the right. -(a) Which inductor carries the larger current?

Consider the two inductors shown below (which are in independent circuits) . The induced emf in each inductor is such that the inductor behaves like a battery with its positive end to the right. -(b) In which is the current changing more rapidly?

In the inductors shown in problem E20T.1, the current shown flowing through each coil must be

Suppose we wrap a solenoid coil around a hollow cardboard cylinder. Now suppose that we insert an iron core into the solenoid. What will happen to the coil's inductance when we insert the iron core? (Explain.)

A coil with a self-inductance of 1H1 \mathrm{H}1H is connected in parallel to a 10−Ω10-\Omega10−Ω light bulb and a 5−V5-\mathrm{V}5−V battery. Very roughly how long would it keep the light bulb lit if the battery was disconnected from the circuit? (Choose the closest answer.)

If we increase the resistance in the LR circuit shown in figure E20.1b, how would this change the rate of decay of the current through the coil?

In an LC circuit, if we increase the capacitor's capacitance (while keeping everything else the same) , the circuit's oscillation frequency will

In an LC circuit, if we increase the initial charge on the capacitor (while keeping everything else the same) , the circuit's oscillation frequency will

A certain utility transformer is designed to step up the emf from 1kV1 \mathrm{kV}1kV to 25kV25 \mathrm{kV}25kV . If the primary has 1000 turns of wire, how many turns of wire does the secondary have?

A coil with a self-inductance of $1 \mathrm{H}$ is connected in parallel to a $10-\Omega$ light bulb and a $5-\mathrm{V}$ battery. Very roughly how long would it keep the light bulb lit if the battery was disconnected from the circuit? (Choose the closest answer.)

A certain utility transformer is designed to step up the emf from $1 \mathrm{kV}$ to $25 \mathrm{kV}$ . If the primary has 1000 turns of wire, how many turns of wire does the secondary have?