Q: What is the value of the electrostatic constant $$K$$ used in Coulomb's law?

$$K = 8.99 \times 10^9$\ \mathrm{N \cdot m^2$ \cdot C$$^{-2}$$}$$

Question 1

A negatively charged rod is brought near (but does not touch) the disk of an electroscope, and then briefly touches the end of the post before being removed. What is the final state of the electroscope?

Accepted Answer

The leaves are deflected because there is an excess of positive charge on the disk and post.

Question 2

Which process is responsible for charging an electroscope when a charged rod is brought near and the post is briefly touched?

Accepted Answer

Charging by induction

Question 3

What is the value of the electrostatic constant $$K$$ used in Coulomb's law?

Accepted Answer

$$K = 8.99 	imes 10^9$\ \mathrm{N \cdot m^2$ \cdot C$$^{-2}$$}$$

Question 4

Two spheres, Sphere 1 and Sphere 2, both have positive charges and are placed close to each other. If the force by Sphere 1 on Sphere 2 is shown as a vector pointing to the right, what is the direction of the force by Sphere 2 on Sphere 1?

Accepted Answer

To the left, with the same magnitude

Question 5

Given two point charges $$q_1 = -3.0$$ 	imes $$10^{-6}$$\ \mathrm{C}$$ at the origin and q_2$ = 5.0 	imes 10$$^{-6}$$\ \mathrm{C} at$$ $$(x = 0.040\ \mathrm{m}, y = 0.030\ \mathrm{m})$$, what is the magnitude of the electric force exerted on $$q_2 by$$ $$q_1$$?

Accepted Answer

$$54\ \mathrm{N}$$

Question 6

For the same charges as above, what is the $$x-$$component of the electric force exerted on $$q_2 by$$ $$q_1$$?

Accepted Answer

$$-43\ \mathrm{N}$$

Question 7

Which of the following best describes the direction of the electric force between two opposite charges?

Accepted Answer

The force is attractive and directed along the line joining the charges.

Question 8

If three charges $$q_1$$, $$q_2$$, and $$q_3$$ are present, what is the net electric force on charge $$q_2$$?

Accepted Answer

$$\vec{F}_{1\ \mathrm{on}\ 2} + \vec{F}_{3\ \mathrm{on}\ 2}$$

Question 9

A central charge $$q is $$placed between two other charges at equal distances above and below it. In case 1, the two surrounding charges have opposite signs; in case 2, both are positive. What is the magnitude of the net force on the center charge in case 2 compared to case 1?

Accepted Answer

The net force in case 2 is larger than in case 1.

Question 10

If the direction of the force from each charge on a central charge $$q is $$reversed, what does this indicate about the sign of $$q$$?

Accepted Answer

The sign of $$q$$ has changed from positive to negative.

Question 11

A charge $$q_3 = 3.0$$ 	imes $$10^{-6}$$\ \mathrm{C}$$ is placed on the y$-axis at y = 0.030$$\ \mathrm{m}$$. Given q_1$ = -3.0 	imes 10$$^{-6}$$\ \mathrm{C} at $$the origin and $$q_2 = 5.0$$ 	imes $$10^{-6}$$\ \mathrm{C}$$ at (x = 0.040$$\ \mathrm{m}, y = 0.030\ \mathrm{m})$$, what is the x$-component of the net force on q_2$?

Accepted Answer

$$41\ \mathrm{N}$$

Question 12

What is the $$y-$$component of the net force on $$q_2 in $$the previous scenario?

Accepted Answer

$$-32\ \mathrm{N}$$

Question 13

Which equation correctly expresses Coulomb's law for the magnitude of the force between two point charges $$q_1$$ and $$q_2$$ separated by distance $$r$$?

Accepted Answer

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

Question 14

In a real-world scenario, two balloons are rubbed with wool and then suspended close to each other. What type of force do they exert on each other?

Accepted Answer

A repulsive electric force

Question 15

A proton and an electron are separated by a distance $$r. $$Which statement is true about the force between them?

Accepted Answer

The force is attractive and equal in magnitude for both particles.

Question 16

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

Accepted Answer

It becomes one-fourth as large.

Question 17

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

Accepted Answer

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

Question 18

A student calculates the net electric force on a charge by summing the forces from all other charges present. Which principle is the student applying?

Accepted Answer

The principle of superposition

Electrostatics: Charging, Coulomb's Law, and Electric Forces

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