Q: A $$20\ \mathrm{nC}$$ charge experiences a $$0.047\ \mathrm{N}$$ electric force. What is the magnitude of the electric field at the position of this charge?

$$E = 2.4 \times 10^6$\ \mathrm{N/C}$$

Q: A typical lightning strike transfers $$2.5\ \mathrm{C} of $$charge from cloud to ground in $$0.20\ \mathrm{ms}. $$What is the average current during the strike?

$$I = 1.25 \times 10^4$\ \mathrm{A}$$

Q: A $$20\ \mathrm{nC}$$ charge is placed in a uniform electric field of $$2.0 \times 10^5$\ \mathrm{N/C}. $$What is the magnitude of the force on the charge?

$$F = 4.0 \times 10$$^{-3}$$\ \mathrm{N}$$

Question 1

Two point charges, $$q_1 = +16$$\ \mu\mathrm{C}$$ at the origin and q_2$ = -20\ \mu\mathrm{C} at$$ $$(0.40\ \mathrm{m},\ 0.20\ \mathrm{m})$$, are placed in vacuum. What is the magnitude of the electric force on $$q_1$$ due to $$q_2$$? (Use $$k = 8.99 	imes 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$.)

Accepted Answer

$$F = 16.0\ \mathrm{N}$$

Question 2

A $$20\ \mathrm{nC}$$ charge experiences a $$0.047\ \mathrm{N}$$ electric force. What is the magnitude of the electric field at the position of this charge?

Accepted Answer

$$E = 2.4 	imes 10^6$\ \mathrm{N/C}$$

Question 3

What is the direction of the electric force on a positive charge placed at $$(x, y) = (0.40\ \mathrm{m}, 0.20\ \mathrm{m})$$ due to a negative charge at the origin?

Accepted Answer

Toward the origin

Question 4

A $$1.0\ \mu\mathrm{F}$$ capacitor is to be charged to store $$2.0\ \mathrm{J} of $$energy. What potential difference should be applied?

Accepted Answer

$$V = 2000\ \mathrm{V}$$

Question 5

A $$60\ \mathrm{W}$$, $$240\ \Omega$$ light bulb filament is $$60\ \mathrm{cm}$$ long. If the potential difference across the filament is $$120\ \mathrm{V}$$, what is the strength of the electric field inside the filament?

Accepted Answer

$$E = 200\ \mathrm{V/m}$$

Question 6

A $$1500\ \mathrm{W}$$ hair dryer operates at $$120\ \mathrm{V}. $$What is the resistance of the hair dryer?

Accepted Answer

$$R = 9.6\ \Omega$$

Question 7

A $$60\ \mathrm{W}$$ electric blanket runs at $$12\ \mathrm{V}. $$What is the current through the wire in the blanket?

Accepted Answer

$$I = 5.0\ \mathrm{A}$$

Question 8

A typical lightning strike transfers $$2.5\ \mathrm{C} of $$charge from cloud to ground in $$0.20\ \mathrm{ms}. $$What is the average current during the strike?

Accepted Answer

$$I = 1.25 	imes 10^4$\ \mathrm{A}$$

Question 9

A $$4.80 	imes 10$$^{-19}$$\ \mathrm{C}$$ charge is placed on the x-axis in a region where the electric potential increases in the $$+x$$ direction but does not change in the $$y or$$ $$z$$ direction. If the particle moves from point $$a to $$point $$b$$ along the x-axis, increasing its kinetic energy by $$1.60 	imes 10$$^{-18}$$\ \mathrm{J}$$, what is the potential difference $$V_a - V_b$$?

Accepted Answer

$$V_a - V_b = 3.33\ \mathrm{V}$$

Question 10

Two $$4.0\ \mathrm{cm} 	imes 4.0\ \mathrm{cm}$$ square aluminum electrodes, spaced $$0.60\ \mathrm{mm}$$ apart, are connected to a $$200\ \mathrm{V}$$ battery. What is the capacitance of the system? ($$\$$varepsilon_0$$ = 8.85 	imes 10$$^{-12}$$\ \mathrm{F/m})$$

Accepted Answer

$$C = 2.4\ \mathrm{pF}$$

Question 11

A $$^7\mathrm{Li}^+$$ ion (charge $$+e$$, mass $$4u) is $$accelerated from rest to a speed of $$1.3 	imes 10^6$\ \mathrm{m/s}. $$What potential difference is needed? ($$e = 1.6 	imes 10$$^{-19}$$\ \mathrm{C}$$, $$u = 1.66 	imes 10$$^{-27}$$\ \mathrm{kg})$$

Accepted Answer

$$\Delta V = 35.2\ \mathrm{V}$$

Question 12

A $$1.0\ \mathrm{k\Omega}$$ resistor is needed. How can you connect four $$1.0\ \mathrm{k\Omega}$$ resistors to produce an equivalent resistance of $$0.25\ \mathrm{k\Omega}$$?

Accepted Answer

All in parallel

Question 13

A $$1.0\ \mu\mathrm{F}$$ capacitor has half the capacitance and twice the potential difference as a $$2.0\ \mu\mathrm{F}$$ capacitor. What is the ratio $$U_1$$/$$U_2 of $$their stored energies?

Accepted Answer

$$U_1$$/$$U_2 = 2$

Question 14

A neutral conducting sphere is placed between two parallel charged plates. What happens to the electric field lines near the sphere?

Accepted Answer

The field lines bend toward the sphere and become denser near its surface

Question 15

A $$4.80 	imes 10$$^{-19}$$\ \mathrm{C}$$ charge moves from point $$a to $$point $$c in $$the $$y$$ direction in a region of constant electric potential. What is the change in its potential energy?

Accepted Answer

$$\Delta U = 0$$

Question 16

A $$20\ \mathrm{nC}$$ charge is placed in a uniform electric field of $$2.0 	imes 10^5$\ \mathrm{N/C}. $$What is the magnitude of the force on the charge?

Accepted Answer

$$F = 4.0 	imes 10$$^{-3}$$\ \mathrm{N}$$

Question 17

Which of the following best describes the direction of the electric field that will balance the weight of a proton near Earth's surface?

Accepted Answer

Downward

Question 18

A battery increases the electric potential energy of $$0.040\ \mathrm{C} of $$charge by $$0.70\ \mathrm{J} as it $$moves from the negative to the positive terminal. What is the emf of the battery?

Accepted Answer

$$\mathcal{E} = 17.5\ \mathrm{V}$$

Electric Forces, Fields, Potential, and Circuits: College Physics Study Guide

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