Q: A neutral lithium atom has 3 protons, 3 neutrons, and 3 electrons. What is the net charge of a lithium ion with 2 electrons?

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

Q: What is the magnitude of the charge of a single proton?

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

Q: Which equation from Maxwell’s equations relates the electric field to charge density?

$\nabla \cdot \mathbf{E} = \frac{\rho}{\varepsilon_0}$

Q: Two point charges, $q_1 = +2.0\ \mu\mathrm{C}$ and $q_2 = -3.0\ \mu\mathrm{C}$, are placed $0.50\ \mathrm{m}$ apart. What is the magnitude of the force between them?

$F = \frac{(9.0 \times 10^9) \times (2.0 \times 10^{-6}) \times (3.0 \times 10^{-6})}{(0.50)^2} = 0.216\ \mathrm{N}$

Question 1

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

Accepted Answer

The total electric charge in any closed system remains constant over time.

Question 2

A neutral lithium atom has 3 protons, 3 neutrons, and 3 electrons. What is the net charge of a lithium ion with 2 electrons?

Accepted Answer

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

Question 3

Which of the following best explains why a charged comb can pick up small pieces of paper?

Accepted Answer

The comb polarizes the molecules in the paper, causing an attractive force.

Question 4

What is the magnitude of the charge of a single proton?

Accepted Answer

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

Question 5

Which of the following materials is a good conductor of electricity?

Accepted Answer

Copper

Question 6

A negatively charged plastic rod is brought near a neutral metal ball. What happens to the electrons in the ball?

Accepted Answer

They are repelled away from the rod, causing the side nearest the rod to become positively charged.

Question 7

Which equation from Maxwell’s equations relates the electric field to charge density?

Accepted Answer

$
abla \cdot \mathbf{E} = \frac{ho}{\varepsilon_0}$

Question 8

Two point charges, $q_1 = +2.0\ \mu\mathrm{C}$ and $q_2 = -3.0\ \mu\mathrm{C}$, are placed $0.50\ \mathrm{m}$ apart. What is the magnitude of the force between them?

Accepted Answer

$F = \frac{(9.0 	imes 10^9) 	imes (2.0 	imes 10^{-6}) 	imes (3.0 	imes 10^{-6})}{(0.50)^2} = 0.216\ \mathrm{N}$

Question 9

Which statement about electric charge is correct?

Accepted Answer

There are exactly two kinds of electric charge: positive and negative.

Question 10

A negatively charged rod is brought near a neutral insulator. What is the resulting force between the rod and the insulator?

Accepted Answer

An attractive force due to polarization of the insulator.

Question 11

Which process describes charging a metal object by induction?

Accepted Answer

Bringing a charged object near the metal, grounding the metal, then removing the ground and the charged object.

Question 12

If you rub a balloon on your hair and stick it to a wall, which phenomenon is responsible for the balloon sticking?

Accepted Answer

Polarization of molecules in the wall.

Question 13

Which of the following is true about the force between two point charges according to Coulomb’s Law?

Accepted Answer

It is inversely proportional to the square of the distance between the charges.

Question 14

What is the value of the Coulomb constant $k$ used in Coulomb’s Law?

Accepted Answer

$9.0 	imes 10^9\ \mathrm{N}\cdot\mathrm{m}^2/\mathrm{C}^2$

Question 15

A paint sprayer uses electrostatics to paint a grounded metal object. What is the role of the induced charge on the object?

Accepted Answer

It attracts the oppositely charged paint droplets, improving paint coverage.

Question 16

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

Accepted Answer

Conductors allow free movement of electric charge, while insulators do not.

Question 17

Which of the following is a consequence of the quantization of electric charge?

Accepted Answer

All observable charge is an integer multiple of $e = 1.60 	imes 10^{-19}\ \mathrm{C}$.

Question 18

If three point charges are placed on a straight line, how do you determine the net force on one of the charges?

Accepted Answer

By vector addition of the individual forces from the other two charges.

Electric Charge and Electric Fields: Fundamentals and Applications

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