Q: A 10-A current flows through a wire for 2.0 minutes. How much charge has passed through this wire?

$$Q = I \Delta t = 10\,\mathrm{A} \times 120\,\mathrm{s} = 1200\,\mathrm{C}$$

Q: A system of four capacitors is connected across a 90-V voltage source. If the equivalent capacitance is $$C_{eq}$$, what is the total charge stored in the system?

$$Q = C_{eq} \times 90\,\mathrm{V}$$

Q: A 100-W light bulb is connected to a 120-V outlet. How much energy does it use in 24 hours?

$$E = P \times t = 100\,\mathrm{W} \times 24 \times 3600\,\mathrm{s} = 8.64 \times 10^6$\,\mathrm{J}$$

Question 1

A 10-A current flows through a wire for 2.0 minutes. How much charge has passed through this wire?

Accepted Answer

$$Q = I \Delta t = 10\,\mathrm{A} 	imes 120\,\mathrm{s} = 1200\,\mathrm{C}$$

Question 2

Which equation correctly relates the resistance $$R of a $$wire to its resistivity $$\rho$$, length $$L$$, and cross-sectional area $$A$$?

Accepted Answer

$$R = \rho \dfrac{L}{A}$$

Question 3

A 25-m wire of diameter 0.30 mm draws 0.499 A when connected across a 3.0-V potential difference. What is the resistance of the wire?

Accepted Answer

$$R = \dfrac{V}{I} = \dfrac{3.0\,\mathrm{V}}{0.499\,\mathrm{A}} \approx 6.01\,\Omega$$

Question 4

Which of the following best describes an ohmic material?

Accepted Answer

A material for which the current is directly proportional to the applied potential difference.

Question 5

A device is rated at 250 W when connected across a 120-V dc power supply. What current does it draw under normal operation?

Accepted Answer

$$I = \dfrac{P}{V} = \dfrac{250\,\mathrm{W}}{120\,\mathrm{V}} \approx 2.08\,\mathrm{A}$$

Question 6

Which of the following is the correct expression for the equivalent resistance $$R_{eq} of $$three resistors $$R_1$$, $$R_2$$, and $$R_3$$ connected in parallel?

Accepted Answer

$$\dfrac{1}{R_{eq}} = \dfrac{1}{R_1$} + \dfrac{1}{R_2$} + \dfrac{1}{R_3$}$$

Question 7

If five 2.0-$$\Omega$$ resistors are connected as shown in the provided figure (with three in parallel and two in series with the parallel group), what is the equivalent resistance between points a and b?

Accepted Answer

$$R_{eq} = 2.0\,\Omega$$

Question 8

Which law states that the sum of the currents entering a junction equals the sum of the currents leaving the junction?

Accepted Answer

Kirchhoff’s Junction Law

Question 9

A battery with emf $$\mathcal{E}$$ and internal resistance $$r is $$connected to a resistor $$R. $$What is the current in the circuit?

Accepted Answer

$$I = \dfrac{\mathcal{E}}{R + r}$$

Question 10

Which of the following best describes the energy transformation in a simple circuit with a battery and a resistor?

Accepted Answer

Chemical energy $$\rightarrow$$ electrical potential energy $$\rightarrow$$ kinetic energy $$\rightarrow$$ thermal energy

Question 11

A system of four capacitors is connected across a 90-V voltage source. If the equivalent capacitance is $$C_{eq}$$, what is the total charge stored in the system?

Accepted Answer

$$Q = C_{eq} 	imes 90\,\mathrm{V}$$

Question 12

Which of the following is the correct loop equation for a closed circuit with resistors $$R_1$$, $$R_2$$, and $$R_3$$ and batteries $$V_1$$, $$V_2$$, and $$V_3 as $$shown in the provided figure?

Accepted Answer

$$V_1$$ - $$I_1$$ $$R_1$$ - $$V_2$$ - $$I_2$$ $$R_2$$ - $$V_3$$ - $$I_3$$ $$R_3 = 0$

Question 13

A 100-W light bulb is connected to a 120-V outlet. How much energy does it use in 24 hours?

Accepted Answer

$$E = P 	imes t = 100\,\mathrm{W} 	imes 24 	imes 3600\,\mathrm{s} = 8.64 	imes 10^6$\,\mathrm{J}$$

Question 14

Which of the following statements about the nervous system and electricity is correct?

Accepted Answer

Action potentials travel as waves along the axon, and myelin increases conduction speed by saltatory conduction.

Question 15

Which of the following is the correct formula for the power dissipated by a resistor $$R$$ with current $$I$$ flowing through it?

Accepted Answer

$$P = I^2$ R$$

Question 16

If three batteries with emfs $$\mathcal{E}_1$$, $$\mathcal{E}_2$$, and $$\mathcal{E}_3$$ are connected in series, what is the total emf?

Accepted Answer

$$\mathcal{E}_{total} = \mathcal{E}_1 + \mathcal{E}_2 + \mathcal{E}_3$$

Question 17

A wire has a resistance of $$5\,\Omega at$$ $$20^\circC. If $$the temperature increases and the resistivity increases by 10%, what is the new resistance?

Accepted Answer

$$R_{new} = 5\,\Omega 	imes 1.10 = 5.5\,\Omega$$

Question 18

Which of the following is the correct formula for the equivalent capacitance $$C_{eq} of $$three capacitors $$C_1$$, $$C_2$$, and $$C_3$$ connected in series?

Accepted Answer

$$\dfrac{1}{C_{eq}} = \dfrac{1}{C_1$} + \dfrac{1}{C_2$} + \dfrac{1}{C_3$}$$

Current, Resistance, and Circuits: Study Notes for College Physics

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