Q: An electron is released from rest in a uniform electric field of $$E = 100\ \mathrm{N/C}$$ and travels a distance $$d = 0.01\ \mathrm{m}. $$What is its final speed? (Electron charge $$e = 1.6 \times 10$$^{-19}$$\ \mathrm{C}$$, mass $$m_e = 9.1 \times 10$$^{-31}$$\ \mathrm{kg})$$

$$v = 6 \times 10^5$\ \mathrm{m/s}$$

Question 1

Which of the following correctly expresses the total electric potential energy $$U of $$three point charges $$q_1$$, $$q_2$$, and $$q_3$$ separated by distances $$r_{12}$$, $$r_{23}$$, and $$r_{13}$$?

Accepted Answer

$$U = \frac{1}{4\pi\$$varepsilon_0$$} \left( \frac{q_1$ q_2$}{r_{12}} + \frac{q_2$ q_3$}{r_{23}} + \frac{q_1$ q_3$}{r_{13}} \right)$$

Question 2

A field is a physical quantity that has a value at every location in space. Which of the following is a vector field?

Accepted Answer

Air flow

Question 3

The electric field $$\vec{E} at a $$point due to a point charge $$Q is $$given by which of the following equations?

Accepted Answer

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

Question 4

Which statement best describes the direction of the electric field produced by a negative point charge?

Accepted Answer

The field points toward the charge.

Question 5

If three charges are arranged as shown in the first image, which pairs contribute to the total potential energy of the system?

Accepted Answer

All three pairs: $$q_1$$ and $$q_2$$, $$q_2$$ and $$q_3$$, $$q_1$$ and $$q_3$$

Question 6

A proton is placed in a uniform electric field pointing to the right. What is the direction of the force on the proton?

Accepted Answer

To the right, parallel to the electric field

Question 7

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

Accepted Answer

The net electric field is the vector sum of the fields produced by each charge.

Question 8

In an electric field diagram, what does the density of field lines represent?

Accepted Answer

The strength of the electric field

Question 9

A negative test charge is placed at point B in the electric field diagram of two positive charges. In which direction does the force on the test charge point?

Accepted Answer

Toward both positive charges

Question 10

A parallel plate capacitor creates a uniform electric field between its plates. If the charge on the plates is doubled while the area remains constant, what happens to the electric field between the plates?

Accepted Answer

It doubles

Question 11

An electron is released from rest in a uniform electric field of $$E = 100\ \mathrm{N/C}$$ and travels a distance $$d = 0.01\ \mathrm{m}. $$What is its final speed? (Electron charge $$e = 1.6 	imes 10$$^{-19}$$\ \mathrm{C}$$, mass $$m_e = 9.1 	imes 10$$^{-31}$$\ \mathrm{kg})$$

Accepted Answer

$$v = 6 	imes 10^5$\ \mathrm{m/s}$$

Question 12

Which of the following is true about electric field lines?

Accepted Answer

They never intersect.

Question 13

If the electric field at a point is $$\vec{E}$$ and a charge $$q is $$placed at that point, what is the force on the charge?

Accepted Answer

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

Question 14

A system consists of two charges, $$+Q$$ and $$-Q$$, separated by a distance $$d. $$Where is the electric field strongest?

Accepted Answer

Near the charges

Question 15

Which of the following best describes the motion of a charged particle in a uniform electric field if its initial velocity is perpendicular to the field lines?

Accepted Answer

The trajectory is parabolic.

Question 16

If the electric field at a point is zero, what can you conclude about the arrangement of charges?

Accepted Answer

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

Question 17

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

Accepted Answer

They can cross each other.

Question 18

A test charge is placed in an electric field and experiences a force. If the test charge is doubled, what happens to the force?

Accepted Answer

It doubles.

Question 19

Which of the following best describes the relationship between electric field lines and equipotential surfaces?

Accepted Answer

Electric field lines are always perpendicular to equipotential surfaces.

Electric Fields and Potential Energy: Study Notes for College Physics

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