Q: What is the net charge of an atom with 16 protons and 17 electrons?

$$q = (16 - 17) \times e = -1.6 \times 10$$^{-19}$$ \ \mathrm{C}$$

Q: How many electrons are needed to make up a charge of $$-1.5 \times 10$$^{-7}$$ \ \mathrm{C}$$?

$$n = \frac{1.5 \times 10$$^{-7}$$}{1.6 \times 10$$^{-19}$$} = 9.4 \times 10$$^{11}$$ electrons

Q: Two identical charges are connected by a 1 m cable with a 10 N tension. What is the magnitude of each charge?

$$q = \sqrt{\frac{F r^2$}{k_e}} = \sqrt{\frac{10 \times 1^2$}{9 \times 10^9$}} = 3.33 \times 10$$^{-5}$$ \ \mathrm{C}$$

Question 1

Which of the following statements best describes the property of electric charge?

Accepted Answer

Electric charge is a property of matter, similar to mass, and is responsible for electric forces.

Question 2

What is the net charge of an atom with 16 protons and 17 electrons?

Accepted Answer

$$q = (16 - 17) 	imes e = -1.6 	imes 10$$^{-19}$$ \ \mathrm{C}$$

Question 3

How many electrons are needed to make up a charge of $$-1.5 	imes 10$$^{-7}$$ \ \mathrm{C}$$?

Accepted Answer

$$n = \frac{1.5 	imes 10$$^{-7}$$}{1.6 	imes 10$$^{-19}$$} = 9.4 	imes 10$$^{11}$$ electrons

Question 4

Which material property allows electrons to move freely, making it a good conductor?

Accepted Answer

The material allows electrons to move freely throughout its structure.

Question 5

What is the result of rubbing a plastic rod with fur?

Accepted Answer

Electrons are transferred from the fur to the plastic rod, giving the rod a negative charge.

Question 6

Which of the following best describes the process of charging by induction?

Accepted Answer

A neutral conductor is charged without direct contact by bringing a charged object nearby and grounding the conductor.

Question 7

According to the law of conservation of charge, what happens when two objects are brought into contact and then separated?

Accepted Answer

The total charge of the two objects remains constant, but charge may be redistributed between them.

Question 8

Coulomb's Law gives the force between two point charges as:

Accepted Answer

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

Question 9

If the force between two charges is $$F$$ when the distance is $$d$$, what is the force if the distance is doubled?

Accepted Answer

$$F' = \frac{F}{4}$$

Question 10

Two identical charges are connected by a 1 m cable with a 10 N tension. What is the magnitude of each charge?

Accepted Answer

$$q = \sqrt{\frac{F r^2$}{k_e}} = \sqrt{\frac{10 	imes 1^2$}{9 	imes 10^9$}} = 3.33 	imes 10$$^{-5}$$ \ \mathrm{C}$$

Question 11

A $$1 \ \mathrm{C}$$ charge is placed at the center of a square with four $$-2 \ \mathrm{C}$$ charges at the corners. What is the direction of the net force on the center charge?

Accepted Answer

The net force is zero due to symmetry.

Question 12

If you add electrons to an object and its charge increases by $$16 \ \mu\mathrm{C}$$, how many electrons were added?

Accepted Answer

$$n = \frac{16 	imes 10$$^{-6}$$}{1.6 	imes 10$$^{-19}$$} = 1 	imes 10$$^{14}$$ electrons

Question 13

Which of the following best describes polarization in conductors?

Accepted Answer

Charges rearrange within the conductor, but there is no net charge transfer.

Question 14

A water sample has a density of $$1 \ \mathrm{g/cm}^3$$, a molecular weight of $$18 \ \mathrm{g/mol}$$, and 10 electrons per molecule. How many electrons are in $$20 \ \mathrm{cm}^3 of $$water?

Accepted Answer

$$N = \frac{20}{18} 	imes 6.022 	imes 10$$^{23}$$ 	imes 10 = 6.7 	imes 10$$^{24}$$ electrons

Question 15

Which of the following is true about the interaction between like and unlike charges?

Accepted Answer

Like charges repel, and unlike charges attract.

Question 16

If two spheres, one with $$+3 \ \mathrm{C}$$ and one with $$-1 \ \mathrm{C}$$, are brought into contact and then separated, what is the final charge on each sphere?

Accepted Answer

$$q = \frac{3 + (-1)}{2} = 1 \ \mathrm{C}$$

Question 17

Rank the pairs of charges in an equilateral triangle (with charges $$2e$$, $$3e$$, and $$5e at $$the vertices) by the magnitude of the electric force between them, from greatest to least.

Accepted Answer

Pair with $$3e$$ and $$5e$$ \u003e pair with $$2e$$ and $$5e$$ \u003e pair with $$2e$$ and $$3e$$

Question 18

A $$-1 \ \mathrm{C}$$ charge is placed between a $$1 \ \mathrm{C}$$ and a $$2 \ \mathrm{C}$$ charge, separated by $$10 \ \mathrm{cm}. In $$which direction will the $$-1 \ \mathrm{C}$$ charge move?

Accepted Answer

Toward the $$2 \ \mathrm{C}$$ charge

Question 19

What is the ratio of the electric force to the gravitational force between a proton and an electron in a hydrogen atom?

Accepted Answer

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

Study Notes: Electric Charges and Forces (Ch. 22)

Study Guide - Practice Questions

Study Guide - Flashcards