Q: What is the SI unit of electric charge, and how many elementary charges does it represent?

Coulomb (C); $$6.25 \times 10$$^{18}$$ elementary charges

Q: A lithium atom loses one electron to become a lithium ion. What is the resulting net charge on the ion?

$$+1.60 \times 10$$^{-19}$$\ \mathrm{C}$$

Q: A proton ($$q = +1.60 \times 10$$^{-19}$$\ \mathrm{C}) is $$placed in a uniform electric field of $$E = 4.00 \times 10^3$\ \mathrm{N\ C$$^{-1}$$}. $$What is the force acting on the proton?

$$6.4 \times 10$$^{-16}$$\ \mathrm{N}$$

Q: A system consists of three charges: $$q_1 = 2.0$$\ \mathrm{C}$$, q_2$ = 1.0\ \mathrm{C}$$, and $$q_3 = 4.0$$\ \mathrm{C}$$, arranged in a right triangle with q_1$ and q_2$ separated by 3.0$$\ \mathrm{m}$$ and q_2$ and q_3$ separated by 4.0$$\ \mathrm{m}$$. What is the net force on q_2$ due to q_1$ and q_3$? (k = 9.0$$ \times $$10^9$$\ \mathrm{N\ $$m^2$$\ $$C^{-2}$$}$$)

$$14.0 \times 10^9$\ \mathrm{N}$$

Question 1

Which of the following best describes Coulomb’s Law?

Accepted Answer

It states that the force between two charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

Question 2

What is the SI unit of electric charge, and how many elementary charges does it represent?

Accepted Answer

Coulomb (C); $$6.25 	imes 10$$^{18}$$ elementary charges

Question 3

A lithium atom loses one electron to become a lithium ion. What is the resulting net charge on the ion?

Accepted Answer

$$+1.60 	imes 10$$^{-19}$$\ \mathrm{C}$$

Question 4

Which law states that the net amount of charge produced in any transfer process is zero?

Accepted Answer

Law of conservation of charge

Question 5

Two point charges, $$Q = 3.0\ \mu\mathrm{C}$$ and $$q = 4.0\ \mu\mathrm{C}$$, are placed $$0.20\ \mathrm{m}$$ apart in a vacuum. Calculate the magnitude of the force between them. ($$k = 9.0 	imes 10^9$\ \mathrm{N\ m^2$\ C$$^{-2}$$})$$

Accepted Answer

$$2.7\ \mathrm{N}$$

Question 6

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

Accepted Answer

Electric field lines can cross each other.

Question 7

A proton ($$q = +1.60 	imes 10$$^{-19}$$\ \mathrm{C}) is $$placed in a uniform electric field of $$E = 4.00 	imes 10^3$\ \mathrm{N\ C$$^{-1}$$}. $$What is the force acting on the proton?

Accepted Answer

$$6.4 	imes 10$$^{-16}$$\ \mathrm{N}$$

Question 8

Which scenario best illustrates the concept of induction?

Accepted Answer

A charged balloon sticks to a neutral wall by attracting opposite charges to the surface.

Question 9

Given two charges $$Q$$ and $$q$$ separated by a distance $$r$$, which equation correctly gives the electric field strength at a point due to $$Q$$?

Accepted Answer

$$E = \frac{kQ}{r^2$}$$

Question 10

A system consists of three charges: $$q_1 = 2.0$$\ \mathrm{C}$$, q_2$ = 1.0\ \mathrm{C}$$, and $$q_3 = 4.0$$\ \mathrm{C}$$, arranged in a right triangle with q_1$ and q_2$ separated by 3.0$$\ \mathrm{m}$$ and q_2$ and q_3$ separated by 4.0$$\ \mathrm{m}$$. What is the net force on q_2$ due to q_1$ and q_3$? (k = 9.0$$ 	imes $$10^9$$\ \mathrm{N\ $$m^2$$\ $$C^{-2}$$}$$)

Accepted Answer

$$14.0 	imes 10^9$\ \mathrm{N}$$

Question 11

Which of the following is the correct expression for the force between two point charges in a vacuum?

Accepted Answer

$$F = \frac{1}{4\pi\$$varepsilon_0$$} \frac{Qq}{r^2$}$$

Question 12

A student rubs a plastic rod with a cloth, and the rod becomes negatively charged. Which statement best explains this observation?

Accepted Answer

Electrons are transferred from the cloth to the rod.

Question 13

Which of the following best describes an electric field?

Accepted Answer

A region of space where a charged particle experiences a force.

Question 14

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

Accepted Answer

It becomes one-fourth as large.

Question 15

Which of the following is a property of electric field lines?

Accepted Answer

They never cross each other.

Question 16

A charge of $$+2.0\ \mu\mathrm{C} is $$placed at a point in space. What is the direction of the electric field at a point directly to the right of the charge?

Accepted Answer

To the right, away from the charge

Question 17

Which of the following best describes the elementary charge?

Accepted Answer

The magnitude of the electric charge carried by a single electron or proton

Question 18

A student calculates the force between two charges using $$F = \frac{kQq}{r^2$}. If$$ $$Q is $$doubled and $$r is $$halved, by what factor does the force change?

Accepted Answer

The force increases by a factor of 8.

Electrostatics: Charge, Coulomb’s Law, and Electric Fields

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