Q: What is the value of the elementary charge $$e$$?

$$e = 1.602176634 \times 10$$^{-19}$$\ \mathrm{C}$$

Q: What is the value of the Coulomb constant $$k$$?

$$k = 8.988 \times 10^9$\ \mathrm{N \cdot m^2$/C^2$$}$

Question 1

Which of the following statements about electric charge is correct?

Accepted Answer

Electric charge is a scalar quantity that can be positive, negative, or zero.

Question 2

What is the value of the elementary charge $$e$$?

Accepted Answer

$$e = 1.602176634 	imes 10$$^{-19}$$\ \mathrm{C}$$

Question 3

Which of the following materials is a conductor?

Accepted Answer

Metal

Question 4

A positively charged comb is brought near small pieces of neutral paper. The paper is attracted to the comb. What is the best explanation for this phenomenon?

Accepted Answer

The electric field of the comb polarizes the molecules in the paper, causing attraction.

Question 5

According to Coulomb's law, what is the magnitude of the force between two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r$$?

Accepted Answer

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

Question 6

What is the value of the Coulomb constant $$k$$?

Accepted Answer

$$k = 8.988 	imes 10^9$\ \mathrm{N \cdot m^2$/C^2$$}$

Question 7

If two charges of $$+2\ \mu\mathrm{C}$$ are placed 10 cm apart, what is the direction of the force on each charge?

Accepted Answer

The charges repel each other, so the force on each is directed away from the other.

Question 8

Which of the following best describes the electric field produced by a point charge $$q at a $$distance $$r$$?

Accepted Answer

$$\vec{E} = k \frac{q}{r^2$} \hat{r}$$

Question 9

A small positive test charge is placed in the electric field of a negative point charge. In which direction does the force on the test charge point?

Accepted Answer

Toward the negative charge

Question 10

What is the unit of the electric field?

Accepted Answer

Newton per coulomb (N/C)

Question 11

Which of the following statements about electric field lines is correct?

Accepted Answer

Electric field lines point away from positive charges and toward negative charges.

Question 12

A dipole consists of charges $$+q$$ and $$-q$$ separated by a distance $$d. $$What is the magnitude of its electric dipole moment $$p$$?

Accepted Answer

$$p = qd$$

Question 13

What is the direction of the electric dipole moment vector $$\vec{p}$$?

Accepted Answer

From the negative charge to the positive charge

Question 14

What is the torque $$	au on an $$electric dipole of moment $$\vec{p} in a $$uniform electric field $$\vec{E} at an $$angle $$\phi$$?

Accepted Answer

$$	au = pE \sin \phi$$

Question 15

Which of the following best describes the potential energy $$U of a $$dipole in a uniform electric field $$\vec{E}$$?

Accepted Answer

$$U = -\vec{p} \cdot \vec{E}$$

Question 16

A proton and an electron are placed 1 nm apart in vacuum. Which force is stronger: the electric force between them or the gravitational force between them?

Accepted Answer

The electric force is much stronger than the gravitational force.

Question 17

Which of the following is true about the conservation of electric charge?

Accepted Answer

The total electric charge in an isolated system remains constant.

Question 18

A metal rod is brought near a charged object but does not touch it. The metal rod becomes polarized. What is the best explanation for this?

Accepted Answer

Free electrons in the metal move in response to the external electric field, causing polarization.

Question 19

If the distance between two point charges is doubled, what happens to the magnitude of the force between them according to Coulomb's law?

Accepted Answer

The force decreases by a factor of 4.

Electric Charge, Coulomb’s Law, and Electric Fields

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