Q: A proton is moved from point A to point B in an electric field. If the electric potential at A is 5 V and at B is 2 V, what is the change in electric potential energy of the proton?

$$\Delta U = q \Delta V = (1.6 \times 10$$^{-19}$$\,\text{C})(2\,\text{V} - 5\,\text{V}) = -4.8 \times 10$$^{-19}$$\,\text{J}$$

Q: A heart defibrillator uses a capacitor charged to 5000 V with a capacitance of $$1.0 \times 10$$^{-6}$$ F. How much energy is stored in the capacitor?

$$U = \frac{1}{2}CV^2$ = \frac{1}{2} \times 1.0 \times 10$$^{-6}$$ \times (5000)^2$ = 12.5\,\text{J}$$

Question 1

Which of the following statements best describes the relationship between electric potential energy and the work done by the electric force?

Accepted Answer

The change in electric potential energy is the negative of the work done by the electric force: $$\Delta U = -W_{	ext{electric}}.$$

Question 2

A proton is moved from point A to point B in an electric field. If the electric potential at A is 5 V and at B is 2 V, what is the change in electric potential energy of the proton?

Accepted Answer

$$\Delta U = q \Delta V = (1.6 	imes 10$$^{-19}$$\,	ext{C})(2\,	ext{V} - 5\,	ext{V}) = -4.8 	imes 10$$^{-19}$$\,	ext{J}$$

Question 3

Which equation correctly relates the electric field $$E to $$the rate of change of electric potential $$V$$ with respect to distance $$x$$?

Accepted Answer

$$E = -\frac{dV}{dx}$$

Question 4

Which of the following statements about equipotential surfaces is correct?

Accepted Answer

Equipotential surfaces are perpendicular to electric field lines.

Question 5

An electron moves through a potential difference of 12 V. How much energy does it gain in electron volts (eV)?

Accepted Answer

12 eV

Question 6

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 7

A capacitor is connected to a battery. Which of the following statements about the charge $$Q on $$the capacitor and the voltage $$V$$ across it is correct?

Accepted Answer

$$Q = CV$$

Question 8

The capacitance of a parallel-plate capacitor is given by which formula?

Accepted Answer

$$C = \frac{\$$epsilon_0$$ A}{d}$$

Question 9

A parallel-plate capacitor is filled with a dielectric material of dielectric constant $$K. $$How does the capacitance change?

Accepted Answer

$$C = K \frac{\$$epsilon_0$$ A}{d}$$

Question 10

Which of the following best explains why a dielectric increases the capacitance of a capacitor?

Accepted Answer

The dielectric reduces the electric field within the capacitor, allowing more charge to be stored for the same potential.

Question 11

What is the energy stored in a charged capacitor with capacitance $$C$$ and voltage $$V$$?

Accepted Answer

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

Question 12

A heart defibrillator uses a capacitor charged to 5000 V with a capacitance of $$1.0 	imes 10$$^{-6}$$ F. How much energy is stored in the capacitor?

Accepted Answer

$$U = \frac{1}{2}CV^2$ = \frac{1}{2} 	imes 1.0 	imes 10$$^{-6}$$ 	imes (5000)^2$ = 12.5\,	ext{J}$$

Question 13

Which of the following best describes the energy density $$u in an $$electric field?

Accepted Answer

$$u = \frac{1}{2}\$$epsilon_0$$ E^2$

Question 14

A digital signal is less sensitive to noise than an analog signal because:

Accepted Answer

Digital signals use discrete values, making them less affected by small fluctuations.

Question 15

Which of the following statements about binary numbers in digital electronics is correct?

Accepted Answer

Binary numbers use only the digits 0 and 1 to represent values.

Question 16

In a cathode ray tube (CRT), what causes electrons to move from the cathode to the anode?

Accepted Answer

A voltage source creates an electric field that accelerates the electrons.

Question 17

Which of the following is true about the electric potential due to an electric dipole at a point far from the dipole?

Accepted Answer

The potential drops off as $$\frac{1}{r^2$}$$, where $$r is $$the distance from the dipole.

Question 18

A parallel-plate capacitor has plates of area $$A = 0.02\,	ext{m}^2$$ separated by $$d = 0.001\,	ext{m}$$ and is filled with a dielectric of $$K = 5. $$What is its capacitance?

Accepted Answer

$$C = K \frac{\$$epsilon_0$$ A}{d} = 5 	imes \frac{8.85 	imes 10$$^{-12}$$ 	imes 0.02}{0.001} = 5 	imes 1.77 	imes 10$$^{-10}$$ = 8.85 	imes 10$$^{-10}$$\,	ext{F}$$

Question 19

Which of the following best describes the function of an electrocardiogram (ECG or EKG)?

Accepted Answer

It detects heart defects by measuring changes in electric potential on the surface of the heart.

Chapter 17: Electric Potential – Structured Study Notes

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