Question 1

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

Accepted Answer

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

Question 2

A glass rod is rubbed with silk, and electrons are transferred from the glass to the silk. What is the resulting charge on the glass rod?

Accepted Answer

The glass rod becomes positively charged due to a deficiency of electrons.

Question 3

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

Accepted Answer

Copper

Question 4

A neutral lithium atom has 3 protons, 4 neutrons, and 3 electrons. If it loses one electron, what is the resulting ion called and what is its net charge?

Accepted Answer

A positive lithium ion with a net charge of $$+1e$$

Question 5

Which equation correctly expresses Coulomb’s Law for the magnitude of the electric force between two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r$$?

Accepted Answer

$$F = k_e \frac{|q_1$ q_2$|}{r^2$}$$

Question 6

Two point charges, $$q_1 = +25$$\ \mathrm{nC}$$ and q_2$ = -75\ \mathrm{nC}$$, are separated by a distance $$r = 3.0\ \mathrm{cm}. $$What is the direction of the electric force that $$q_1$$ exerts on $$q_2$$?

Accepted Answer

Attractive, directed toward $$q_1$$

Question 7

Which of the following best explains why water is an effective solvent for ionic compounds?

Accepted Answer

Water molecules are polar, allowing them to surround and separate ions.

Question 8

If you rub a balloon against your hair and the balloon becomes negatively charged, what happens to the mass of your hair?

Accepted Answer

It will decrease.

Question 9

Three objects, A, B, and C, are brought close to each other, two at a time. A and B repel, B and C repel. Which of the following must be true?

Accepted Answer

Objects A and C possess charges of the same sign.

Question 10

A charged rod is brought near a neutral metal sphere, and the sphere is then grounded. What is the resulting charge on the sphere after the ground connection is removed?

Accepted Answer

The sphere has a net charge opposite in sign to the rod.

Question 11

Which of the following best describes the difference between conductors and insulators?

Accepted Answer

Conductors allow free movement of charge; insulators do not.

Question 12

Which of the following is the correct expression for the ratio of the electric force to the gravitational force between two alpha particles, each with charge $$q$$ and mass $$m$$, separated by distance $$r$$?

Accepted Answer

$$\frac{F_e}{F_g} = \frac{1}{4\pi\$$varepsilon_0$$ G} \frac{q^2$}{m^2$}$$

Question 13

Three point charges are placed at the vertices of an equilateral triangle. Charges #1 and #2 are $$+q$$, and charge #3 is $$-q. $$What is the direction of the net electric force that charges #2 and #3 exert on charge #1?

Accepted Answer

In the $$+x-$$direction.

Question 14

Which of the following statements about the electric force between two point charges is correct?

Accepted Answer

The force is attractive if the charges are of opposite sign and repulsive if they are of the same sign.

Question 15

A charged comb can pick up small pieces of paper even if the paper is neutral. What is the best explanation for this phenomenon?

Accepted Answer

The electric field of the comb induces a separation of charge in the paper, causing attraction.

Question 16

Which of the following is a real-world application of electrostatic induction?

Accepted Answer

Electrostatic painting of automobiles

Question 17

If two charges $$q_1$$ and $$q_2$$ are separated by a distance $$r$$, and the force between them is $$F$$, what will be the new force if the distance is doubled?

Accepted Answer

$$F/4$$

Question 18

Which of the following best describes the superposition principle as applied to electric forces?

Accepted Answer

The total force on a charge is the vector sum of the forces exerted by all other charges.

Electric Charge and Coulomb’s Law: Foundations of Electrostatics

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