Q: A $$2.0 \ \mathrm{g}$$ marble is suspended between two charged plates, $$6.0 \ \mathrm{cm}$$ apart, and remains stationary. If the electric field between the plates is $$3.3 \times 10^3$ \ \mathrm{N/C}$$, what is the charge on the marble? (Take $$g = 9.8 \ \mathrm{m/s^2$})$$

$$5.9 \times 10$$^{-6}$$ \ \mathrm{C}$$

Question 1

Which of the following statements about electric charge is CORRECT?

Accepted Answer

Electric charge is a scalar quantity and can be positive or negative.

Question 2

According to the rules of electrical interaction, what happens when two protons are brought close together?

Accepted Answer

They repel each other because they have like charges.

Question 3

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

Accepted Answer

$$1.60 	imes 10$$^{-19}$$ C

Question 4

Which of the following best describes the quantum description of electric interaction?

Accepted Answer

Point charges are indivisible entities with no size or structure.

Question 5

A hydrogen atom has an electron orbiting at a distance of $$1 	imes 10$$^{-10}$$ m from the nucleus. If the electron moves at 0.7c$, which of the following is a valid concern with using Coulomb's law in this scenario?

Accepted Answer

Coulomb's law assumes instantaneous action at a distance, which is not valid at relativistic speeds.

Question 6

Which equation correctly expresses the electric 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 7

Compare the magnitude of the electric force to the gravitational force between two electrons separated by $$1.0 	imes 10$$^{-10}$$ m. Which is true?

Accepted Answer

The electric force is much stronger than the gravitational force.

Question 8

What is the electric field at a distance $$r$$ from a point charge $$q$$?

Accepted Answer

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

Question 9

A test charge $$q_0 is $$placed in an electric field $$\vec{E}. $$What is the force experienced by the test charge?

Accepted Answer

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

Question 10

If two charges $$+q$$ and $$-q$$ are placed a distance $$d$$ apart, what is the direction of the electric field at the midpoint between them?

Accepted Answer

The electric field points from $$+q to$$ $$-q.$$

Question 11

Which of the following is a correct unit for the electric field?

Accepted Answer

$$\mathrm{N/C}$$

Question 12

A small sphere carries a charge of $$0.756 \ \mathrm{nC}. $$How many excess electrons does it have? (Use $$e = 1.6 	imes 10$$^{-19}$$ C)

Accepted Answer

$$4.7 	imes 10^9$

Question 13

Which of the following is a correct statement about the electric field due to a point charge?

Accepted Answer

The electric field is directed toward the charge if it is negative.

Question 14

A $$2.0 \ \mathrm{g}$$ marble is suspended between two charged plates, $$6.0 \ \mathrm{cm}$$ apart, and remains stationary. If the electric field between the plates is $$3.3 	imes 10^3$ \ \mathrm{N/C}$$, what is the charge on the marble? (Take $$g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$5.9 	imes 10$$^{-6}$$ \ \mathrm{C}$$

Question 15

Which of the following is a limitation of Coulomb's law?

Accepted Answer

It is only valid when the distance between charges is much greater than their size.

Question 16

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

Accepted Answer

It becomes one-fourth as large.

Question 17

A proton and an electron are placed $$1.0 	imes 10$$^{-10}$$ m apart. What is the direction of the electric force on the electron?

Accepted Answer

Toward the proton

Question 18

Which of the following best describes the electric field at a point in space?

Accepted Answer

It is a vector field representing the force per unit charge at each point in space.

Question 19

A test charge of $$2.0 	imes 10$$^{-6}$$ C experiences a force of 0.01$ N in an electric field. What is the magnitude of the electric field at that point?

Accepted Answer

$$5.0 	imes 10$$^{3}$$ \ \mathrm{N/C}$$

Question 20

Which of the following is a correct comparison between electric and gravitational forces?

Accepted Answer

Electric forces can be attractive or repulsive, while gravitational forces are always attractive.

Electrostatics: Charge, Coulomb's Law, and the Electric Field

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