Q: Given two point charges, $$q_1 = +2e$ and q_2$ = -3e$$, separated by a distance $$r$$, what is the magnitude of the force between them according to Coulomb’s law?

$$F = K \frac{2e \times 3e}{r^2$}$$

Q: Which of the following is the correct value for the elementary charge $$e$$?

$$e = 1.6 \times 10$$^{-19}$$ C

Question 1

Which of the following statements best explains why most macroscopic objects do not exhibit strong electrical forces, despite the electromagnetic force being much stronger than gravity at the atomic scale?

Accepted Answer

Most macroscopic objects are electrically neutral, containing equal numbers of protons and electrons, so the net charge is nearly zero.

Question 2

According to Coulomb’s law, what is the direction of the force between two charges $$q_1$$ and $$q_2 if$$ $$q_1q_2 \u003c 0$$?

Accepted Answer

The force is attractive and points toward the other charge.

Question 3

Which of the following best describes the principle of superposition as it applies to electrostatic forces?

Accepted Answer

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

Question 4

Given two point charges, $$q_1 = +2e$ and q_2$ = -3e$$, separated by a distance $$r$$, what is the magnitude of the force between them according to Coulomb’s law?

Accepted Answer

$$F = K \frac{2e 	imes 3e}{r^2$}$$

Question 5

A blue charge $$q is $$placed on a line with a red charge $$Q$$ and a yellow charge $$-Q$$, as shown in the image. If $$r_{-+} \u003c r_{++}$$, which statement is correct about the net force on the blue charge?

Accepted Answer

The net force points to the left because the red charge is closer and its force is stronger.

Question 6

Which of the following is a correct expression for the gravitational force between an electron and a proton separated by a distance $$r$$?

Accepted Answer

$$F_g = G \frac{m_e m_p}{r^2$}$$

Question 7

If the force between two charges is $$F$$, what will be the force if the distance between them is doubled, according to Coulomb’s law?

Accepted Answer

The force will be one-fourth as large.

Question 8

Which of the following best explains why a charged plastic rod attracts small pieces of paper, but a charged metal rod does not?

Accepted Answer

Plastic can induce polarization in the paper, while the metal rod cannot hold charge effectively due to its conductivity.

Question 9

Which of the following is the correct value for the elementary charge $$e$$?

Accepted Answer

$$e = 1.6 	imes 10$$^{-19}$$ C

Question 10

Which law or theorem connects the conservation of electric charge to a fundamental symmetry in physics?

Accepted Answer

Noether’s theorem

Question 11

A system consists of three charges: $$Q$$, $$-Q$$, and $$q$$ arranged in a line as shown in the image. If $$Q$$ and $$-Q$$ are close together, what kind of system do they form and what is its net charge?

Accepted Answer

They form a dipole with net charge zero.

Question 12

Which of the following best describes the quantization of electric charge?

Accepted Answer

Charge is always an integer multiple of the elementary charge $$e$$ for fundamental particles.

Question 13

If the force between two charges is $$F$$, what happens to the force if both charges are doubled while the distance remains the same?

Accepted Answer

The force becomes four times larger.

Question 14

Which of the following is the correct expression for the ratio of the electrostatic force to the gravitational force between an electron and a proton?

Accepted Answer

$$\frac{F_e}{F_g} = \frac{K e^2$}{G m_e m_p}$$

Question 15

Which of the following is NOT a consequence of the electromagnetic force?

Accepted Answer

The gravitational attraction between planets

Question 16

A student rubs a plastic rod with fur and brings it near small pieces of paper, which are attracted to the rod. Which process best explains this attraction?

Accepted Answer

The rod induces a polarization in the paper, causing an attractive force.

Question 17

Which of the following is the correct value for Coulomb’s constant $$K$$?

Accepted Answer

$$K = 8.99 	imes 10^9$ N·m^2$/C^2$

Question 18

Which of the following best describes the direction of the force between two like charges according to Coulomb’s law?

Accepted Answer

The force is repulsive and points away from the other charge.

Question 19

If a system of charges is rearranged but no charge is added or removed, which law guarantees that the total charge remains the same?

Accepted Answer

Conservation of charge

Electric Charge and Coulomb’s Law: Foundations of Electrostatics

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