Q: A group of four charges is arranged at the corners of a rectangle as shown: $Q_1 = +2\ \mathrm{nC}$, $Q_2 = -4\ \mathrm{nC}$, $Q_3 = -6\ \mathrm{nC}$, $Q_4 = +4\ \mathrm{nC}$. What is the total work required to assemble this group from infinity?

$4.3 \times 10^{-6}\ \mathrm{J}$

Question 1

Refer to the graph of electric potential $V$ as a function of $r$ (in meters). Over which interval is the magnitude of the electric field the largest?

Accepted Answer

From $r = 3$ m to $r = 4$ m

Question 2

A negative charge is moved from point A to point B along an equipotential surface. Which statement is true?

Accepted Answer

No work is required to move the negative charge from point A to point B.

Question 3

Two point charges of opposite sign are moved farther apart. What happens to the potential energy of the system relative to infinity?

Accepted Answer

It decreases.

Question 4

A parallel-plate capacitor is connected to a battery and allowed to charge. A dielectric slab is inserted while the battery remains connected. What happens?

Accepted Answer

The charge on the capacitor increases.

Question 5

A cylindrical wire has resistance $R$ and resistivity $\rho$. If both its length and diameter are cut in half, what is its new resistance?

Accepted Answer

$2R$

Question 6

A $100\ \mathrm{W}$ light bulb is connected to a $110\ \mathrm{V}$ source. What is the resistance of the bulb?

Accepted Answer

$120\ \Omega$

Question 7

A parallel-plate capacitor is charged and then disconnected from the battery. The plates are slowly pulled apart. What happens to the potential difference between the plates?

Accepted Answer

It increases.

Question 8

A wire of resistivity $\rho$ is replaced by a wire of the same material but four times as long. If the resistance is to remain the same, what must happen to the diameter?

Accepted Answer

It must be $2$ times the original diameter.

Question 9

A battery charges a parallel-plate capacitor fully and is then removed. The plates are then slowly pulled apart. What happens to the energy stored in the capacitor?

Accepted Answer

It increases.

Question 10

Refer to the equipotential map. At which point (a, b, or c) is the magnitude of the electric field the greatest?

Accepted Answer

At point b

Question 11

A group of four charges is arranged at the corners of a rectangle as shown: $Q_1 = +2\ \mathrm{nC}$, $Q_2 = -4\ \mathrm{nC}$, $Q_3 = -6\ \mathrm{nC}$, $Q_4 = +4\ \mathrm{nC}$. What is the total work required to assemble this group from infinity?

Accepted Answer

$4.3 	imes 10^{-6}\ \mathrm{J}$

Question 12

In the circuit shown, if $i_a = 15\ \mathrm{A}$, $i_b = 11\ \mathrm{A}$, and $i_c = 13\ \mathrm{A}$, what is $i_1$?

Accepted Answer

$i_1 = 15\ \mathrm{A} - 11\ \mathrm{A} = 4\ \mathrm{A}$

Question 13

A parallel-plate capacitor with area $A$ and separation $d$ is connected to a battery and charged. A dielectric with constant $K$ is inserted, filling the space. What happens to the capacitance?

Accepted Answer

It increases by a factor of $K$.

Question 14

A wire is stretched so its length increases and diameter decreases. What happens to its resistance and resistivity?

Accepted Answer

Resistance increases, resistivity stays the same.

Question 15

A parallel-plate capacitor is charged to voltage $V$ and then disconnected. If the plate separation is doubled, what happens to the potential difference?

Accepted Answer

It doubles.

Question 16

A light bulb is rated at $60\ \mathrm{W}$ and $110\ \mathrm{V}$. If it is operated at a reduced voltage so that it draws $36\ \mathrm{W}$, what is the operating voltage?

Accepted Answer

$72\ \mathrm{V}$

Question 17

As more resistors are added in parallel across a constant voltage source, what happens to the power supplied by the source?

Accepted Answer

It increases.

Question 18

In the circuit with the junction shown, if $4\ \mathrm{A}$ and $5\ \mathrm{A}$ enter a junction and $2\ \mathrm{A}$ and $3\ \mathrm{A}$ leave, what is the value and direction of $I_1$?

Accepted Answer

$I_1 = 4\ \mathrm{A} + 5\ \mathrm{A} - 2\ \mathrm{A} - 3\ \mathrm{A} = 4\ \mathrm{A}$ in

Physics 2 Midterm Review: Electric Potential, Circuits, and Capacitance

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