Q: Which constant is used in Coulomb's Law and what is its approximate value?

Coulomb's constant, $$k = 8.99 \times 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$

Question 1

Which of the following best describes the force between two point charges according to Coulomb's Law?

Accepted Answer

It is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

Question 2

A negatively charged comb can attract small pieces of neutral paper. Which physical principle explains this phenomenon?

Accepted Answer

The comb polarizes the molecules in the paper, causing an attractive force due to induced dipoles.

Question 3

Given two point charges $$q_1 = 2$$ 	imes $$10^{-6}$$\ \mathrm{C}$$ and q_2$ = -3 	imes 10$$^{-6}$$\ \mathrm{C}$$ separated by $$r = 0.05\ \mathrm{m}$$, what is the magnitude of the electric force between them? Use $$k = 8.99 	imes 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$.

Accepted Answer

$$F = 21.6\ \mathrm{N}$$

Question 4

Which equation correctly expresses Coulomb's Law for the magnitude of the electric force between two point charges?

Accepted Answer

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

Question 5

If the distance between two point charges is doubled, how does the magnitude of the electric force between them change?

Accepted Answer

It becomes one-fourth as great.

Question 6

Which of the following statements about Newton's third law and electric forces is correct?

Accepted Answer

The force exerted by $$q_1 on$$ $$q_2 is $$equal in magnitude but opposite in direction to the force exerted by $$q_2 on$$ $$q_1.$$

Question 7

A charged comb attracts a neutral insulator. What happens to the charges within the molecules of the insulator?

Accepted Answer

The electrons in the molecules shift slightly toward the comb, causing the positive charges to be closer to the comb.

Question 8

Which of the following is the SI unit of electric charge?

Accepted Answer

Coulomb

Question 9

Consider three point charges: $$q_1 = 2e$, q_2$ = -3e$$, and $$q_3 = -5e$, placed in a line with equal spacing d$. What principle allows you to calculate the net force on q_2$?

Accepted Answer

The principle of superposition of electric forces.

Question 10

If two charges $$q_1$$ and $$q_2$$ are both positive, what is the direction of the force each exerts on the other?

Accepted Answer

They repel each other.

Question 11

A student claims that the electric force between two charges is always attractive. Which scenario disproves this claim?

Accepted Answer

Two charges of the same sign placed near each other.

Question 12

Which constant is used in Coulomb's Law and what is its approximate value?

Accepted Answer

Coulomb's constant, $$k = 8.99 	imes 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$

Question 13

A charged comb picks up small pieces of paper. Which of the following best explains why the paper is attracted to the comb?

Accepted Answer

The comb induces a polarization in the paper, causing the side closer to the comb to have an opposite charge.

Question 14

Which of the following is true about the direction of the electric force between two point charges?

Accepted Answer

It is along the line joining the two charges and depends on the sign of the charges.

Question 15

A student calculates the electric force between two charges using $$F = k \dfrac{q_1$ q_2$}{r^2$}$$ and gets a negative value. What does the negative sign indicate?

Accepted Answer

The force is attractive.

Question 16

If the magnitude of each charge in a pair is doubled, but the distance between them remains the same, how does the electric force change?

Accepted Answer

It is quadrupled.

Question 17

Which of the following is a correct comparison between Coulomb's Law and Newton's Law of Universal Gravitation?

Accepted Answer

Both laws describe forces that are inversely proportional to the square of the distance between two objects.

Question 18

A neutral insulator is placed near a charged object. What happens to the molecules in the insulator?

Accepted Answer

The charges within the molecules shift slightly, causing polarization.

Question 19

Which of the following best describes the principle of superposition for electric forces?

Accepted Answer

The net force on a charge is the sum of the individual forces exerted by all other charges.

Coulomb’s Law and Electric Force – Study Notes for General Physics II

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