Q: An electric dipole is placed in a uniform electric field $$\vec{E}. $$What is the net force and the torque on the dipole?

Net force is zero, but there is a torque $$\vec{\tau} = \vec{p} \times \vec{E}.$$

Q: A $$-8.0 nC $$charge is placed at the origin. What is the magnitude of the electric field at a point $$2.0 m $$away from the charge? ($$k = 8.99 \times 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$)

$$E = 1.8 \times 10^4$\ \mathrm{N/C}$$

Question 1

Which of the following statements best describes the principle of charge conservation?

Accepted Answer

The total electric charge in any closed system remains constant over time.

Question 2

A neutral atom becomes negatively charged when:

Accepted Answer

It gains extra electrons.

Question 3

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

Accepted Answer

Copper wire

Question 4

According to Coulomb’s Law, the magnitude of the force between two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r is $$given by:

Accepted Answer

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

Question 5

Two charges, $$q_1 = 2.0$$\ \mu C$$ and q_2$ = -2.0\ \mu C$$, are placed 4.0 cm apart. What is the direction of the force on $$q_1$$ due to $$q_2$$?

Accepted Answer

Toward $$q_2 ($$attractive)

Question 6

The electric field $$\vec{E} at a $$point due to a point charge $$q at a $$distance $$r is$$:

Accepted Answer

$$\vec{E} = \frac{1}{4\pi\$$varepsilon_0$$} \frac{q}{r^2$} \hat{r}$$

Question 7

A metal sphere is initially uncharged and is then grounded while a negatively charged rod is brought near it (but not touching). What is the final charge on the sphere after the rod is removed and the ground is disconnected?

Accepted Answer

Positive

Question 8

Which of the following best describes the direction of the electric field lines around a positive point charge?

Accepted Answer

They radiate outward from the charge.

Question 9

A proton and an electron are separated by a distance $$r. $$The electric force between them is much stronger than the gravitational force. Which equation correctly expresses the ratio of electric to gravitational force?

Accepted Answer

$$\frac{F_E}{F_G} = \frac{k q_e q_p}{G m_e m_p}$$

Question 10

A test charge $$q_0 is $$placed in an electric field $$\vec{E}. $$The force experienced by the charge is:

Accepted Answer

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

Question 11

Which of the following is true about the electric field inside a conductor in electrostatic equilibrium?

Accepted Answer

The electric field is zero everywhere inside the conductor.

Question 12

A pair of equal and opposite charges separated by a distance $$d$$ forms an electric dipole. The dipole moment $$\vec{p} is $$given by:

Accepted Answer

$$\vec{p} = q \vec{d}$$, pointing from $$-q to$$ $$+q$$

Question 13

An electric dipole is placed in a uniform electric field $$\vec{E}. $$What is the net force and the torque on the dipole?

Accepted Answer

Net force is zero, but there is a torque $$\vec{	au} = \vec{p} 	imes \vec{E}.$$

Question 14

A $$-8.0 nC $$charge is placed at the origin. What is the magnitude of the electric field at a point $$2.0 m $$away from the charge? ($$k = 8.99 	imes 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$)

Accepted Answer

$$E = 1.8 	imes 10^4$\ \mathrm{N/C}$$

Question 15

Which of the following best describes the difference between electric field lines and electric force diagrams?

Accepted Answer

Field lines show the direction of the electric field at every point, while force diagrams show the force on a specific charge.

Question 16

A small oil droplet is suspended between two horizontal plates with a uniform electric field. If the droplet has a charge $$q$$ and mass $$m$$, what must be the magnitude of the electric field $$E to $$keep the droplet stationary?

Accepted Answer

$$E = \frac{mg}{q}$$

Question 17

If three point charges are placed along a straight line, how do you calculate the net force on the middle charge?

Accepted Answer

By vectorially adding the forces exerted by the other two charges on the middle charge.

Question 18

A water molecule has a dipole moment of $$6.17 	imes 10$$^{-30}$$\ \mathrm{C\cdot m}$$ and a separation of $$3.9 	imes 10$$^{-12}$$\ \mathrm{m}$$ between charges. What is the magnitude of the charge on each end of the dipole?

Accepted Answer

$$q = \frac{6.17 	imes 10$$^{-30}$$}{3.9 	imes 10$$^{-12}$$} = 1.58 	imes 10$$^{-18}$$\ \mathrm{C}$$

Electric Charge and Electric Field: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards