Q: A $$20\ \mathrm{nC}$$ charge is moved from a point where $$V = 150\ \mathrm{V} to a $$point where $$V = -50\ \mathrm{V}. $$How much work is done by the force that moves the charge?

$$2.0 \times 10$$^{-6}$$\ \mathrm{J}$$

Q: A $$2.0\ \mu\mathrm{C}$$ charge is at the origin and a $$-3.0\ \mu\mathrm{C}$$ charge is on the y-axis at $$y = 4.0\ \mathrm{cm}. $$What is the electric potential at a point $$P$$ which is $$3.0\ \mathrm{cm} on $$the x-axis?

$$V = 1.8 \times 10$$^{5}$$\ \mathrm{V}$$

Q: A capacitor is charged so that it stores $$8.0 \times 10$$^{-6}$$\ \mathrm{C} of $$charge at a potential difference of $$2.0 \times 10$$^{3}$$\ \mathrm{V}. $$What is its capacitance?

$$4.0 \times 10$$^{-9}$$\ \mathrm{F}$$

Q: A $$+2.0\ \mathrm{nC}$$ charge is moved in a uniform electric field of $$2.0\ \mathrm{kN/C} a $$distance of $$0.50\ \mathrm{m} at an $$angle of $$60^\circ to $$the field direction. What is the change in electric potential energy?

$$-1.0 \times 10$$^{-9}$$\ \mathrm{J}$$

Q: A $$1.0\ \mu\mathrm{F}$$ capacitor is charged to $$100\ \mathrm{V}. $$How much energy is stored in the capacitor?

$$5.0 \times 10$$^{-3}$$\ \mathrm{J}$$

Q: A $$2.0\ \mathrm{nC}$$ charge is moved from point A to point B in a uniform electric field. The potential at A is $$100\ \mathrm{V}$$ and at B is $$-50\ \mathrm{V}. $$What is the work done by the electric field?

$$-3.0 \times 10$$^{-7}$$\ \mathrm{J}$$

Question 1

A point charge $$q$$ creates an electric field. Which of the following correctly describes how the magnitude of the electric field $$E$$ changes with distance $$r$$ from the charge?

Accepted Answer

It decreases as $$1/r^2.$$

Question 2

Which of the following best describes the electric field between the plates of a parallel-plate capacitor when the plates are charged?

Accepted Answer

The field is uniform and points from the positive to the negative plate.

Question 3

A $$20\ \mathrm{nC}$$ charge is moved from a point where $$V = 150\ \mathrm{V} to a $$point where $$V = -50\ \mathrm{V}. $$How much work is done by the force that moves the charge?

Accepted Answer

$$2.0 	imes 10$$^{-6}$$\ \mathrm{J}$$

Question 4

Which equation gives the potential difference $$\Delta V$$ between two points separated by distance $$d in a $$uniform electric field $$E at an $$angle $$	heta to $$the displacement?

Accepted Answer

$$\Delta V = -Ed \cos 	heta$$

Question 5

A $$2.0\ \mu\mathrm{C}$$ charge is at the origin and a $$-3.0\ \mu\mathrm{C}$$ charge is on the y-axis at $$y = 4.0\ \mathrm{cm}. $$What is the electric potential at a point $$P$$ which is $$3.0\ \mathrm{cm} on $$the x-axis?

Accepted Answer

$$V = 1.8 	imes 10$$^{5}$$\ \mathrm{V}$$

Question 6

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

Accepted Answer

Electric potential is independent of the charge, while electric potential energy depends on the charge.

Question 7

A capacitor is charged so that it stores $$8.0 	imes 10$$^{-6}$$\ \mathrm{C} of $$charge at a potential difference of $$2.0 	imes 10$$^{3}$$\ \mathrm{V}. $$What is its capacitance?

Accepted Answer

$$4.0 	imes 10$$^{-9}$$\ \mathrm{F}$$

Question 8

Which of the following real-world devices relies on the rapid discharge of a capacitor to function?

Accepted Answer

Defibrillator

Question 9

The energy stored in a capacitor is given by which of the following equations?

Accepted Answer

$$U = \frac{1}{2}CV^2$

Question 10

A $$+2.0\ \mathrm{nC}$$ charge is moved in a uniform electric field of $$2.0\ \mathrm{kN/C} a $$distance of $$0.50\ \mathrm{m} at an $$angle of $$60^\circ to $$the field direction. What is the change in electric potential energy?

Accepted Answer

$$-1.0 	imes 10$$^{-9}$$\ \mathrm{J}$$

Question 11

Which of the following best describes the analogy between gravitational potential energy and electric potential energy?

Accepted Answer

Both represent stored energy due to position in a field and decrease as the object moves in the direction of the field.

Question 12

If a positive charge moves in the direction of a uniform electric field, what happens to its electric potential energy?

Accepted Answer

It decreases.

Question 13

Which of the following is the correct unit for capacitance?

Accepted Answer

$$\mathrm{C/V}$$

Question 14

A $$1.0\ \mu\mathrm{F}$$ capacitor is charged to $$100\ \mathrm{V}. $$How much energy is stored in the capacitor?

Accepted Answer

$$5.0 	imes 10$$^{-3}$$\ \mathrm{J}$$

Question 15

Which of the following correctly expresses the relationship between the electric field $$E$$, the potential difference $$V$$, and the distance $$d$$ between parallel capacitor plates?

Accepted Answer

$$E = V/d$$

Question 16

A $$2.0\ \mathrm{nC}$$ charge is moved from point A to point B in a uniform electric field. The potential at A is $$100\ \mathrm{V}$$ and at B is $$-50\ \mathrm{V}. $$What is the work done by the electric field?

Accepted Answer

$$-3.0 	imes 10$$^{-7}$$\ \mathrm{J}$$

Question 17

Which of the following statements about the energy stored in a capacitor is true?

Accepted Answer

It is proportional to the square of the charge stored.

Question 18

If the distance between the plates of a parallel-plate capacitor is doubled while keeping the charge constant, what happens to the potential difference between the plates?

Accepted Answer

It doubles.

Question 19

Which of the following best explains why a pacemaker uses a capacitor in its circuit?

Accepted Answer

To store electrical energy and release it in controlled pulses to stimulate the heart.

Question 20

A $$5.0\ \mu\mathrm{F}$$ capacitor is connected to a $$12\ \mathrm{V}$$ battery. How much charge is stored on the capacitor?

Accepted Answer

$$6.0 	imes 10$$^{-5}$$\ \mathrm{C}$$

Electric Fields, Potential, and Capacitors: Study Notes

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