Q: According to Coulomb’s Law, what is the magnitude of the force between two point charges $$q_1 = +2.0$$ \ \mu C$$ and q_2$ = -2.0 \ \mu C$$ separated by $$0.50 \ m in $$air?

$$F = 1.44 \times 10$$^{-1}$$ \ N$$

Question 1

Which of the following statements best describes the conservation of electric charge during the process of rubbing a glass rod with silk, as shown in the first image?

Accepted Answer

Electrons are transferred from the glass rod to the silk, making the glass rod positively charged and the silk negatively charged.

Question 2

A negatively charged rod is brought near a neutral conducting sphere, as shown in the second image. What is the primary mechanism responsible for the observed charge separation?

Accepted Answer

Electrons within the sphere are repelled by the rod, causing electron deficiency on the near side and electron buildup on the far side.

Question 3

Which of the following best explains why a charged comb can pick up small pieces of paper, as shown in the fourth image?

Accepted Answer

The comb induces a separation of charge in the paper, resulting in an attractive force.

Question 4

According to Coulomb’s Law, what is the magnitude of the force between two point charges $$q_1 = +2.0$$ \ \mu C$$ and q_2$ = -2.0 \ \mu C$$ separated by $$0.50 \ m in $$air?

Accepted Answer

$$F = 1.44 	imes 10$$^{-1}$$ \ N$$

Question 5

Which equation correctly expresses the electric field $$\vec{E} at a $$distance $$r$$ from a point charge $$q$$?

Accepted Answer

$$\vec{E} = \dfrac{kq}{r^2$} \hat{r}$$

Question 6

A test charge $$q_0 is $$placed in an electric field $$\vec{E}. $$What is the force $$\vec{F}_0$$ experienced by the test charge?

Accepted Answer

$$\vec{F}_0 = q_0$ \vec{E}$$

Question 7

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

Accepted Answer

Electric field lines start on negative charges and end on positive charges.

Question 8

A disk of radius $$R$$ has a uniform surface charge density $$\sigma. $$What is the electric field at a point on the axis of the disk a distance $$x$$ from its center?

Accepted Answer

$$E = \dfrac{\sigma}{2\$$epsilon_0$$} \left(1 - \dfrac{1}{\sqrt{R^2$/x^2 + 1$$}}\right)$

Question 9

If the electric field at a point is zero, which of the following must be true?

Accepted Answer

The vector sum of all electric fields from all charges at that point is zero.

Question 10

A charged ring of radius $$a$$ carries total charge $$Q$$ uniformly distributed. What is the electric field at a point on the axis of the ring a distance $$x$$ from the center?

Accepted Answer

$$E = \dfrac{kQx}{(x^2$ + a^2$)^{3/2}$$}$

Question 11

Which of the following best describes the direction of the electric field produced by a positive point charge?

Accepted Answer

Radially outward from the charge.

Question 12

A parallel plate capacitor is connected to a 100 V battery and the plates are separated by 1.0 cm. What is the magnitude of the electric field between the plates?

Accepted Answer

$$E = 1.0 	imes 10^4$ \ N/C$$

Question 13

Which of the following is a correct statement about the force between two charges according to Coulomb’s Law?

Accepted Answer

The force is inversely proportional to the square of the distance between the charges.

Question 14

A neutral insulator is attracted to a negatively charged comb, as shown in the fifth image. What is the best explanation for this attraction?

Accepted Answer

The insulator becomes polarized, with positive charges closer to the comb and negative charges farther away, resulting in a net attractive force.

Question 15

If two identical spheres are each given the same number of excess electrons and placed 20.0 cm apart, the force between them is $$3.33 	imes 10$$^{-21}$$ \ N. $$How many excess electrons are on each sphere? ($$e = 1.6 	imes 10$$^{-19}$$ \ C)$$

Accepted Answer

Each sphere has $$n = 1.15 	imes 10^3$ excess electrons.

Question 16

Which of the following is true about the electric field produced by a uniformly charged disk at a point along its axis, far from the disk ($$R \gg x$$)?

Accepted Answer

$$E = \dfrac{\sigma}{2\$$epsilon_0$$}$$

Question 17

Which of the following is NOT a property of electric field lines?

Accepted Answer

They can cross each other.

Question 18

A positive charge is placed in a region where the electric field is directed to the right. In which direction will the force on the charge act?

Accepted Answer

To the right, in the direction of the electric field.

Question 19

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

Accepted Answer

The total electric field at a point is the vector sum of the electric fields produced by each charge.

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