Question 1

Which of the following statements best describes the principle of conservation of charge?

Accepted Answer

The total charge in an isolated system remains constant over time.

Question 2

A glass rod is rubbed with silk and becomes positively charged. What happens to the electrons during this process?

Accepted Answer

Electrons are transferred from the glass rod to the silk.

Question 3

Which of the following materials is most likely to be a good conductor of electricity?

Accepted Answer

Copper

Question 4

A negatively charged balloon sticks to a neutral wall. Which of the following best explains this phenomenon?

Accepted Answer

The negative charge on the balloon repels electrons in the wall, inducing a positive charge on the wall's surface.

Question 5

What is the magnitude of the electrostatic force between two point charges, $q_1 = 2 	imes 10^{-6}\ \mathrm{C}$ and $q_2 = -3 	imes 10^{-6}\ \mathrm{C}$, separated by a distance of $0.05\ \mathrm{m}$ in vacuum? Use $k = 8.99 	imes 10^9\ \mathrm{N\cdot m^2/C^2}$.

Accepted Answer

$F = 21.6\ \mathrm{N}$

Question 6

Which of the following best describes the difference between the gravitational force and the electrostatic force?

Accepted Answer

Electrostatic force can be both attractive and repulsive, while gravitational force is always attractive.

Question 7

A small metal sphere with mass $m$ and charge $q$ is held a distance $d$ above an identical fixed sphere with the same charge. If the upper sphere is released, what will happen?

Accepted Answer

It will accelerate upward due to electrostatic repulsion and downward due to gravity.

Question 8

Two protons are separated by a distance $r$. The ratio of the electrostatic force to the gravitational force between them is closest to:

Accepted Answer

$1.2 	imes 10^{36}$

Question 9

A neutral atom becomes a positive ion when:

Accepted Answer

It loses one or more electrons.

Question 10

Which of the following statements about charge quantization is correct?

Accepted Answer

The charge on any object is always an integer multiple of the elementary charge $e$.

Question 11

Four point charges are placed at the corners of a square of side $L$. Two adjacent corners have charge $+Q$ and the other two have charge $-Q$. What is the direction of the net force on a positive test charge $q$ placed at the center of the square?

Accepted Answer

Along the positive $x$-axis

Question 12

A small metal bead A with charge $25\ \mathrm{nC}$ is touched to a neutral bead B. After separation, the beads are placed $5.0\ \mathrm{cm}$ apart and the force between them is $5.4 	imes 10^{-4}\ \mathrm{N}$. Which of the following is true?

Accepted Answer

Bead A has a greater charge than bead B after separation.

Question 13

Which of the following best describes the function of an electroscope?

Accepted Answer

It detects the presence and magnitude of electric charge.

Question 14

If each of four spheres has the same total charge $+Q$ but different sizes, which sphere has the largest charge density?

Accepted Answer

The smallest sphere

Question 15

A charge $+3q$ is placed at $x=0$ and a charge $-q$ is placed at $x=d$. Where can a third charge be placed so that it is in equilibrium?

Accepted Answer

To the left of both charges ($x < 0$)

Question 16

Which of the following is the correct expression for Coulomb's law for the magnitude of the force between two point charges $q_1$ and $q_2$ separated by a distance $r$?

Accepted Answer

$F = \dfrac{k|q_1||q_2|}{r^2}$

1/15 Electric Charge, Coulomb’s Law, and Force Interactions

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