Question 1

A steady electric current passes through a wire with a narrow region as shown. What happens to the drift velocity of the moving charges as they go from region A to region B and then to region C?

Accepted Answer

The drift velocity increases from A to B and decreases from B to C.

Question 2

A cylindrical wire has a resistance $$R$$ and resistivity $$\rho. If $$its length and diameter are BOTH cut in half, what will be its resistance?

Accepted Answer

$$4R$$

Question 3

A cylindrical wire has a resistance $$R$$ and resistivity $$\rho. If $$its length and diameter are BOTH cut in half, what will be its resistivity?

Accepted Answer

$$\rho$$

Question 4

In the circuit shown, the switch S is closed. What happens to the brightness of bulb 1?

Accepted Answer

The brightness decreases permanently.

Question 5

In the circuit shown in the figure, all the lightbulbs are identical. Which of the following is the correct ranking of the brightness of the bulbs?

Accepted Answer

B and C have equal brightness, and A is the dimmest.

Question 6

Two long straight wires carry currents $$I_1$$ and $$I_2 in $$opposite directions. At which point is the magnetic field zero?

Accepted Answer

D

Question 7

An electron moving in the direction of the $$+x-$$axis enters a magnetic field. If the electron experiences a magnetic deflection in the $$+y$$ direction, the direction of the magnetic field in this region points in the direction of the:

Accepted Answer

$$-x-$$axis

Question 8

In the diagram showing a region with positive and negative charges, what are the signs of the charges at positions 1, 2, and 3?

Accepted Answer

1 is positive, 2 is negative, and 3 is neutral.

Question 9

A light bulb is connected in the circuit shown in the figure with the switch S open and the capacitor uncharged. The battery has no appreciable internal resistance. Which one of the following graphs best describes the brightness $$B of $$the bulb as a function of time $$t$$ after closing the switch?

Accepted Answer

Graph 3

Question 10

An electron, moving toward the west, enters a uniform magnetic field. Because of this field the electron curves upward. The direction of the magnetic field is:

Accepted Answer

Towards the north

Question 11

A capacitor of $$22\ \mu\mathrm{F} is $$charged to $$80\ \mathrm{V}$$ and then connected in series with a $$2.8\ \mathrm{M}\Omega$$ resistor. What is the initial current in the circuit after the switch is closed?

Accepted Answer

$$I_0$$ = \dfrac{$$V_0$$}{R}$$

Question 12

How long will it take for the charge on the capacitor to drop to half its original value in the above RC circuit?

Accepted Answer

$$t = RC \ln 2$$

Question 13

In the circuit with two identical batteries and two resistors, the current through the resistor on the right is $$1/2$$ the current through the resistor on the left. What is the resistance of the resistor on the right?

Accepted Answer

$$2R$$

Question 14

In the circuit shown, what is the total resistance between the terminals of the battery?

Accepted Answer

$$R_{total} = 5\ \Omega + (10\ \Omega \parallel 4\ \Omega)$$

Question 15

For the circuit with $$24\ \mathrm{V}$$ battery, $$5\ \Omega$$, $$10\ \Omega$$, and $$4\ \Omega$$ resistors, what is the current through the $$5\ \Omega$$ resistor?

Accepted Answer

$$I = \dfrac{24}{5 + (10 \parallel 4)}$$

Question 16

A capacitor of $$C is $$charged to voltage $$V_0$$ and then discharged through a resistor $$R. $$What is the expression for the charge $$Q on $$the capacitor as a function of time $$t$$?

Accepted Answer

$$Q(t) = Q_0$ e$$^{-t/RC}$$

Question 17

In a multi-loop circuit, which law is used to write equations for the loops?

Accepted Answer

Kirchhoff's Voltage Law

Question 18

A wire of length $$L$$ and cross-sectional area $$A$$ has resistance $$R. If $$the wire is stretched to double its length without changing its volume, what is its new resistance?

Accepted Answer

$$4R$$

Question 19

A charged particle moves in a circle in a uniform magnetic field. If the speed of the particle is doubled, what happens to the radius of its path?

Accepted Answer

It doubles.

Electric Circuits, Resistivity, and Magnetic Fields: Study Notes and Problem Guide

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