Question 1

A proton and an electron are initially separated by a distance $$r_i$$ and are brought closer together to a distance $$r_f. $$What is the change in electric potential energy of the system?

Accepted Answer

$$\Delta U_e = -k_e e^2$ \left( \frac{r_f - r_i}{r_i r_f} \right)$$

Question 2

Which of the following statements about electric potential energy is correct?

Accepted Answer

It depends only on the positions of the charges, not the path taken.

Question 3

Two positive point charges $$q_1$$ and $$q_2$$ are brought closer together. What must be true about the work done and the change in potential energy?

Accepted Answer

Work is done by an external agent and $$\Delta U_e \u003e 0$$

Question 4

What is the electric potential at a distance $$r$$ from a point charge $$Q$$?

Accepted Answer

$$V = \frac{Q}{4\pi\$$epsilon_0$$ r}$$

Question 5

A charge $$q$$ moves through a potential difference $$\Delta V. $$What is the change in its potential energy?

Accepted Answer

$$\Delta U = q \Delta V$$

Question 6

An electron is accelerated from rest through a potential difference and reaches a speed $$v_f. $$What is the potential difference it was accelerated through?

Accepted Answer

$$\Delta V = \frac{m v_f^2$}{2q}$$

Question 7

Which of the following is true about equipotential surfaces?

Accepted Answer

The electric field is always perpendicular to equipotential surfaces.

Question 8

Given a uniform electric field $$\vec{E} in $$the $$+y$$ direction, what is the potential difference between $$y=0$$ and $$y=a$$?

Accepted Answer

$$V(a) - V(0) = -Ea$$

Question 9

The electric field at a point is related to the electric potential by which of the following expressions?

Accepted Answer

$$\vec{E} = -
abla V$$

Question 10

A conducting sphere is given a net charge. Where does the excess charge reside?

Accepted Answer

It resides entirely on the surface.

Question 11

Which of the following is a correct statement of Gauss's Law?

Accepted Answer

$$\oint \vec{E} \cdot d\vec{A} = \frac{Q_{enc}}{\$$epsilon_0$$}$$

Question 12

A long, straight rod has a uniform charge per unit length $$\lambda. $$Using Gauss's Law, what is the magnitude of the electric field at a distance $$r$$ from the rod?

Accepted Answer

$$E = \frac{\lambda}{2\pi\$$epsilon_0$$ r}$$

Question 13

Which of the following is NOT a property of a conductor in electrostatic equilibrium?

Accepted Answer

The electric field just outside the surface is parallel to the surface.

Question 14

A closed surface encloses a net charge $$Q. $$What is the net electric flux through the surface?

Accepted Answer

$$\Phi_E = \frac{Q}{\$$epsilon_0$$}$$

Question 15

A point charge $$+q is $$placed at the center of a conducting spherical shell with no net charge. What is the induced charge on the inner surface of the shell?

Accepted Answer

$$-q$$

Question 16

If the electric field inside a conductor is zero, what can be said about the electric potential inside the conductor?

Accepted Answer

It is constant throughout the conductor.

Question 17

A charge $$q$$ moves from point $$A to $$point $$B in an $$electric field. The potential at $$A is$$ $$V_A$$ and at $$B is$$ $$V_B. $$What is the work done by the electric field?

Accepted Answer

$$W = q(V_A - V_B)$$

Question 18

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.

Question 19

A system consists of three point charges arranged in a right triangle. Which of the following is the correct expression for the total electric potential energy of the system?

Accepted Answer

$$U_e = k_e \left( \frac{q_1$ q_2$}{r_{12}} + \frac{q_1$ q_3$}{r_{13}} + \frac{q_2$ q_3$}{r_{23}} \right)$$

Question 20

A point P is at a potential of $$500.0\ 	ext{kV}$$ and point S is at $$200.0\ 	ext{kV}. A $$charge of $$+2e$$ moves from P to S. What is the change in its kinetic energy?

Accepted Answer

$$+9.6 	imes 10$$^{-14}$$\ 	ext{J}$$

Electric Potential and Gauss’ Law – Study Notes

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