Q: Two point charges, $$q_1 = +2$$ \ \mu\mathrm{C}$$ and q_2$ = -2 \ \mu\mathrm{C}$$, are separated by a distance of $$0.1\ \mathrm{m}. $$What is the magnitude of the force between them? (Use $$k_e = 8.99 \times 10^9$ \ \mathrm{N\cdot m^2$/C^2$$}$)

$$3.6 \times 10^2$\ \mathrm{N}$$

Question 1

Which of the following statements about electric charge is TRUE?

Accepted Answer

The total electric charge in a closed system is always conserved.

Question 2

A glass rod is rubbed with silk, resulting in the rod becoming positively charged. What is the best explanation for this phenomenon?

Accepted Answer

Electrons are transferred from the glass rod to the silk.

Question 3

Which of the following materials is most likely to be a good electrical conductor?

Accepted Answer

Copper

Question 4

Two point charges, $$q_1 = +2$$ \ \mu\mathrm{C}$$ and q_2$ = -2 \ \mu\mathrm{C}$$, are separated by a distance of $$0.1\ \mathrm{m}. $$What is the magnitude of the force between them? (Use $$k_e = 8.99 	imes 10^9$ \ \mathrm{N\cdot m^2$/C^2$$}$)

Accepted Answer

$$3.6 	imes 10^2$\ \mathrm{N}$$

Question 5

Which of the following is NOT a correct rule for drawing electric field lines?

Accepted Answer

Electric field lines can cross each other.

Question 6

A charged rod is brought near two identical metal spheres that are touching each other. The rod does not touch the spheres. What happens if the spheres are separated while the rod is still nearby?

Accepted Answer

One sphere becomes positively charged and the other negatively charged.

Question 7

A point charge $$q is $$placed at the origin. What is the electric field at a distance $$r$$ from the charge?

Accepted Answer

$$E = \dfrac{k_e q}{r^2$}$$

Question 8

Which of the following statements about electric dipoles is correct?

Accepted Answer

The torque on a dipole in a uniform electric field is maximum when the dipole moment is perpendicular to the field.

Question 9

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

Accepted Answer

$$E = \dfrac{1}{4\pi\$$epsilon_0$$} \dfrac{Qx}{(x^2$ + R^2$)^{3/2}$$}$

Question 10

A rod of length $$L$$ has a uniform linear charge density $$\lambda$$ and total charge $$Q. $$What is the value of $$\lambda$$?

Accepted Answer

$$\lambda = Q/L$$

Question 11

A negative point charge is placed near a small piece of neutral paper. The paper is attracted to the charge. What is the best explanation for this attraction?

Accepted Answer

The negative charge induces a separation of charges in the paper, resulting in attraction.

Question 12

Which of the following is a correct statement about the superposition principle for electric fields?

Accepted Answer

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

Question 13

A Van de Graaff generator is used in a physics demonstration. Which of the following best describes its function?

Accepted Answer

It uses a moving belt to accumulate large amounts of electric charge on a hollow metal sphere.

Question 14

A continuous line of charge has a linear charge density $$\lambda = -2y^2$\ \mu\mathrm{C/m}$$ along the $$y-$$axis from $$y=0 to$$ $$y=2\ \mathrm{m}. $$What is the total charge on the line?

Accepted Answer

$$Q = -\dfrac{16}{3}\ \mu\mathrm{C}$$

Question 15

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

Accepted Answer

Electric field lines can form closed loops.

Question 16

A dipole with moment $$\vec{p} is $$placed in a uniform electric field $$\vec{E}. $$What is the potential energy of the dipole?

Accepted Answer

$$U = -\vec{p} \cdot \vec{E}$$

Question 17

A positive test charge is placed in an electric field. The direction of the force on the test charge is:

Accepted Answer

In the direction of the electric field.

Question 18

Which of the following is a correct statement about the quantization of electric charge?

Accepted Answer

Electric charge exists only in multiples of the elementary charge $$e.$$

Question 19

A proton and an electron are placed $$1\ \mathrm{nm}$$ apart in vacuum. What is the direction of the force on the electron due to the proton?

Accepted Answer

Toward the proton.

Question 20

A charged rod is brought near, but does not touch, a metal sphere on an insulating stand. The sphere is momentarily grounded and then the ground is removed. What is the net charge on the sphere after the rod is taken away?

Accepted Answer

The sphere has a net charge opposite in sign to the rod.

Physics 2220: Electricity and Magnetism – Study Notes (Chapter 21: Electric Charge and Electric Field)

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