Q: A proton is released from rest in a uniform electric field of magnitude $$E = 2.0 \times 10^4$\ \mathrm{N/C}. $$What is the change in electric potential energy of the proton after it moves $$0.50\ \mathrm{m} in $$the direction of the field?

$$-1.6 \times 10$$^{-15}$$\ \mathrm{J}$$

Q: A $$2.0\ \mu\mathrm{F}$$ capacitor is charged to $$100\ \mathrm{V}. $$How much energy is stored in the capacitor?

$$1.0 \times 10$$^{-3}$$\ \mathrm{J}$$

Q: A parallel-plate capacitor has plates of area $$0.10\ \mathrm{m}^2$$ separated by $$2.0\ \mathrm{mm} of $$air. What is its capacitance?

$$4.4 \times 10$$^{-10}$$\ \mathrm{F}$$

Q: If the potential at point A is $$+120\ \mathrm{V}$$ and at point B is $$+80\ \mathrm{V}$$, what is the work done by the electric field in moving a $$2.0\ \mu\mathrm{C}$$ charge from A to B?

$$-8.0 \times 10$$^{-5}$$\ \mathrm{J}$$

Question 1

A proton is released from rest in a uniform electric field of magnitude $$E = 2.0 	imes 10^4$\ \mathrm{N/C}. $$What is the change in electric potential energy of the proton after it moves $$0.50\ \mathrm{m} in $$the direction of the field?

Accepted Answer

$$-1.6 	imes 10$$^{-15}$$\ \mathrm{J}$$

Question 2

Which of the following statements about equipotential surfaces is correct?

Accepted Answer

The electric field is always perpendicular to equipotential surfaces.

Question 3

A $$2.0\ \mu\mathrm{F}$$ capacitor is charged to $$100\ \mathrm{V}. $$How much energy is stored in the capacitor?

Accepted Answer

$$1.0 	imes 10$$^{-3}$$\ \mathrm{J}$$

Question 4

Which of the following best describes the electron volt (eV)?

Accepted Answer

The energy gained by an electron moving through a potential difference of one volt.

Question 5

A parallel-plate capacitor has plates of area $$0.10\ \mathrm{m}^2$$ separated by $$2.0\ \mathrm{mm} of $$air. What is its capacitance?

Accepted Answer

$$4.4 	imes 10$$^{-10}$$\ \mathrm{F}$$

Question 6

If the potential at point A is $$+120\ \mathrm{V}$$ and at point B is $$+80\ \mathrm{V}$$, what is the work done by the electric field in moving a $$2.0\ \mu\mathrm{C}$$ charge from A to B?

Accepted Answer

$$-8.0 	imes 10$$^{-5}$$\ \mathrm{J}$$

Question 7

Which of the following changes will increase the capacitance of a parallel-plate capacitor the most?

Accepted Answer

Inserting a dielectric with a large dielectric constant between the plates.

Question 8

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

Accepted Answer

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

Question 9

A capacitor is connected to a battery and then disconnected. If a dielectric is inserted between the plates, what happens to the stored energy?

Accepted Answer

The stored energy decreases.

Question 10

Which of the following is a correct statement about digital and analog signals?

Accepted Answer

Digital signals are less sensitive to noise than analog signals.

Question 11

A heart defibrillator uses a $$200\ \mu\mathrm{F}$$ capacitor charged to $$2000\ \mathrm{V}. $$How much energy is delivered in one discharge?

Accepted Answer

$$400\ \mathrm{J}$$

Question 12

Which of the following best describes the effect of a dielectric inserted into a capacitor?

Accepted Answer

It increases the capacitance by reducing the effective electric field.

Question 13

The energy density $$u in an $$electric field $$E is $$given by which equation?

Accepted Answer

$$u = \dfrac{1}{2} \$$varepsilon_0$$ E^2$

Question 14

A CRT (cathode ray tube) in a television works by:

Accepted Answer

Steering electrons with electric or magnetic fields to strike a screen.

Question 15

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

Accepted Answer

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

Question 16

A $$5.0\ \mathrm{nC}$$ point charge is placed at the origin. What is the electric potential at a point $$0.20\ \mathrm{m}$$ away? ($$\$$varepsilon_0$$ = 8.85 	imes 10$$^{-12}$$\ \mathrm{C^2$/N\cdot m^2$})$$

Accepted Answer

$$225\ \mathrm{V}$$

Question 17

Which of the following is a correct analogy between gravitational and electric potential energy?

Accepted Answer

A larger charge has more electric potential energy, just as a more massive object has more gravitational potential energy.

Question 18

A $$10\ \mu\mathrm{F}$$ capacitor is connected to a $$12\ \mathrm{V}$$ battery. If the battery is removed and the separation between the plates is doubled, what happens to the voltage across the capacitor?

Accepted Answer

It doubles.

Question 19

Which of the following best explains why using electric potential (rather than electric field) can simplify solving some problems?

Accepted Answer

Potential is a scalar, so it can be added algebraically.

Chapter 17: Electric Potential – Structured Study Notes

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