Q: A proton is released from rest at point A and moves to point B in a uniform electric field, as shown in the second image. If the potential difference $$V_A - V_B = 250\ \text{V}$$ and the charge of the proton is $$q = 1.6 \times 10$$^{-19}$$\ \text{C}$$, what is the change in the proton's kinetic energy?

$$1.6 \times 10$$^{-17}$$\ \text{J}$$

Question 1

Which of the following best describes the relationship between electric potential energy ($$U_{el}) $$and electric potential ($$V) $$for a point charge $$q at a $$distance $$r$$ from another charge $$Q$$?

Accepted Answer

$$V = U_{el}/q$$

Question 2

A proton is released from rest at point A and moves to point B in a uniform electric field, as shown in the second image. If the potential difference $$V_A - V_B = 250\ 	ext{V}$$ and the charge of the proton is $$q = 1.6 	imes 10$$^{-19}$$\ 	ext{C}$$, what is the change in the proton's kinetic energy?

Accepted Answer

$$1.6 	imes 10$$^{-17}$$\ 	ext{J}$$

Question 3

Which statement about equipotential surfaces is correct?

Accepted Answer

Equipotential surfaces are always perpendicular to the electric field lines.

Question 4

The electric potential at a distance $$r$$ from a point charge $$q is $$given by which of the following expressions?

Accepted Answer

$$V = \dfrac{1}{4\pi\$$varepsilon_0$$} \dfrac{q}{r}$$

Question 5

A conductor is placed in an external electric field and reaches electrostatic equilibrium. Which of the following statements is true?

Accepted Answer

The electric potential is constant throughout the conductor.

Question 6

If a dielectric material with dielectric constant $$\kappa is $$inserted between two charges, how does the force between the charges change compared to the force in vacuum?

Accepted Answer

The force decreases by a factor of $$\kappa.$$

Question 7

Which of the following best explains why salt dissolves in water but not in air, in terms of electric potential and dielectrics?

Accepted Answer

Water has a high dielectric constant, reducing the attractive force between ions.

Question 8

A charged conductor is grounded by connecting it to the Earth. What happens to the electric potential of the conductor?

Accepted Answer

It becomes equal to the electric potential of the Earth.

Question 9

A particle with charge $$q$$ moves a distance $$d in a $$uniform electric field $$E. $$What is the change in electric potential energy?

Accepted Answer

$$-qEd$$

Question 10

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

Accepted Answer

The electric field is zero and the electric potential is constant.

Question 11

A system consists of three point charges $$q_1$$, $$q_2$$, and $$q_3 at $$distances $$r_{12}$$, $$r_{13}$$, and $$r_{23}$$ from each other. What is the total electric potential energy of the system?

Accepted Answer

$$U_{sys} = \dfrac{1}{4\pi\$$varepsilon_0$$} \left( \dfrac{q_1q_2}{r_{12}} + \dfrac{q_1q_3}{r_{13}} + \dfrac{q_2q_3}{r_{23}} \right)$$

Question 12

Which of the following is a correct statement about the path independence of electric potential?

Accepted Answer

The potential difference between two points depends only on the endpoints, not the path taken.

Question 13

A water molecule is a natural electric dipole. In the presence of an external electric field, what happens to the orientation of water molecules?

Accepted Answer

They tend to align with the electric field.

Question 14

Which of the following best describes the effect of inserting a dielectric material between the plates of a charged capacitor?

Accepted Answer

The capacitance increases by a factor of the dielectric constant $$\kappa.$$

Question 15

If the electric field inside a conductor is zero, what can be said about the distribution of excess charge?

Accepted Answer

Excess charge resides only on the surface of the conductor.

Question 16

A positive charge moves from a region of higher potential to lower potential. What happens to its electric potential energy and kinetic energy?

Accepted Answer

Potential energy decreases, kinetic energy increases.

Question 17

Which of the following is the correct expression for the work done by the electric field when moving a charge $$q$$ through a potential difference $$\Delta V$$?

Accepted Answer

$$W = q\Delta V$$

Question 18

A neutral conductor contains a cavity with a positive charge inside. What is the net electric field inside the conductor (but outside the cavity)?

Accepted Answer

Zero

Question 19

Which of the following best describes the effect of a dielectric on the electric field inside a capacitor?

Accepted Answer

The electric field is reduced by a factor of $$\kappa.$$

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