Question 1

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

Accepted Answer

The total electric charge in any closed system remains constant over time.

Question 2

A glass rod is rubbed with silk and then brought near a plastic rod rubbed with fur. What is the nature of the force between them?

Accepted Answer

Attractive, because they have opposite types of charge.

Question 3

Which equation correctly expresses 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

$$F = \frac{1}{4\pi\$$epsilon_0$$} \frac{|q_1$ q_2$|}{r^2$}$$

Question 4

A neutral lithium atom has 3 protons, 4 neutrons, and 3 electrons. What is the net charge of this atom?

Accepted Answer

Zero, because the number of protons equals the number of electrons.

Question 5

What is the SI unit of electric field strength?

Accepted Answer

Newton per coulomb ($$\mathrm{N/C})$$

Question 6

A point charge $$q$$ produces an electric field at a distance $$r$$ given by which of the following equations?

Accepted Answer

$$E = \frac{1}{4\pi\$$epsilon_0$$} \frac{|q|}{r^2$}$$

Question 7

Which of the following best describes the direction of electric field lines?

Accepted Answer

They point away from positive charges and toward negative charges.

Question 8

A metal ball is charged by induction using a negatively charged rod. What is the net charge on the ball after the process if the ball was initially neutral?

Accepted Answer

Positive, because electrons are repelled from the ball to the ground.

Question 9

If the distance between two point charges is doubled, what happens to the magnitude of the electrostatic force between them?

Accepted Answer

It becomes one-fourth as large.

Question 10

A water molecule is an example of an electric dipole. What happens when it is placed in a uniform electric field?

Accepted Answer

It experiences a net torque but no net force.

Question 11

Which of the following materials is a good conductor of electricity?

Accepted Answer

Copper

Question 12

A charge $$q_0 is $$placed in an electric field $$\vec{E}. $$What is the force $$\vec{F}_0$$ acting on the charge?

Accepted Answer

$$\vec{F}_0 = q_0$ \vec{E}$$

Question 13

Which of the following is true about electric field lines?

Accepted Answer

They never intersect.

Question 14

A positive ion is formed when:

Accepted Answer

An atom loses one or more electrons.

Question 15

Calculate the magnitude of the force between two charges, $$q_1 = 2.0$$ \ \mu\mathrm{C}$$ and q_2$ = -3.0 \ \mu\mathrm{C}$$, separated by $$0.50 \ \mathrm{m} in $$vacuum. Use $$k = 9.0 	imes 10^9$ \ \mathrm{N} \cdot \mathrm{m}^2/\mathrm{C}^2.$$

Accepted Answer

$$F = 0.108 \ \mathrm{N}$$

Question 16

Which of the following best explains why field lines are denser near a charge?

Accepted Answer

The electric field is stronger where field lines are closer together.

Question 17

A negative ion is an atom that:

Accepted Answer

Has more electrons than protons.

Question 18

If a test charge $$q_0 is $$placed at a point where the electric field is $$\vec{E}$$, and the force measured is $$\vec{F}_0$$, what is the relationship between these quantities?

Accepted Answer

$$\vec{E} = \frac{\vec{F}_0}{q_0$}$$

Question 19

Which of the following is a consequence of the quantization of electric charge?

Accepted Answer

All observable charge is an integer multiple of the elementary charge $$e.$$

Electric Charge and Electric Field: Fundamental Concepts and Applications

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