Q: A switch in a circuit is closed for 13 minutes, and an ammeter reads a steady current of 450 mA. How much charge passes through the circuit during this time?

$Q = I \times t = 0.450 \text{ A} \times (13 \times 60) \text{ s} = 351 \text{ C}$

Q: A 8.5 km long aluminium wire with a cross-sectional area of $5.2 \times 10^{-4} \text{ m}^2$ has a resistivity of $2.82 \times 10^{-8} \Omega \cdot \text{m}$. What is its resistance?

$R = \dfrac{\rho L}{A} = \dfrac{2.82 \times 10^{-8} \times 8500}{5.2 \times 10^{-4}} \approx 0.461 \Omega$

Q: If the potential difference across a resistor is 12 V and the current through it is 3 A, what is the power dissipated by the resistor?

$P = VI = 12 \text{ V} \times 3 \text{ A} = 36 \text{ W}$

Q: A battery of emf $6.8 \text{ V}$ and internal resistance $0.4 \Omega$ is connected to a $3.8 \Omega$ resistor. What is the current through the resistor?

$I = \dfrac{E}{R + r} = \dfrac{6.8}{3.8 + 0.4} = 1.6 \text{ A}$

Q: A capacitor of $18 \text{ mF}$ is charged to $380 \text{ mC}$ and then discharged through a $5.0 \Omega$ resistor. What is the time constant of the circuit?

$\tau = RC = 5.0 \Omega \times 18 \times 10^{-3} \text{ F} = 0.09 \text{ s}$

Question 1

Which of the following best describes the direction of conventional current in a circuit?

Accepted Answer

It flows from the positive terminal to the negative terminal of the battery.

Question 2

A switch in a circuit is closed for 13 minutes, and an ammeter reads a steady current of 450 mA. How much charge passes through the circuit during this time?

Accepted Answer

$Q = I 	imes t = 0.450 	ext{ A} 	imes (13 	imes 60) 	ext{ s} = 351 	ext{ C}$

Question 3

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

Accepted Answer

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

Question 4

A 8.5 km long aluminium wire with a cross-sectional area of $5.2 	imes 10^{-4} 	ext{ m}^2$ has a resistivity of $2.82 	imes 10^{-8} \Omega \cdot 	ext{m}$. What is its resistance?

Accepted Answer

$R = \dfrac{ho L}{A} = \dfrac{2.82 	imes 10^{-8} 	imes 8500}{5.2 	imes 10^{-4}} \approx 0.461 \Omega$

Question 5

If the potential difference across a resistor is 12 V and the current through it is 3 A, what is the power dissipated by the resistor?

Accepted Answer

$P = VI = 12 	ext{ V} 	imes 3 	ext{ A} = 36 	ext{ W}$

Question 6

Two resistors, each of $4.8 	ext{ k}\Omega$, are connected in series to a 10 V supply. What is the total power consumed compared to when they are connected in parallel?

Accepted Answer

The series connection uses one-fourth the power of the parallel connection.

Question 7

A battery of emf $6.8 	ext{ V}$ and internal resistance $0.4 \Omega$ is connected to a $3.8 \Omega$ resistor. What is the current through the resistor?

Accepted Answer

$I = \dfrac{E}{R + r} = \dfrac{6.8}{3.8 + 0.4} = 1.6 	ext{ A}$

Question 8

Which statement about resistors in parallel is correct?

Accepted Answer

The total resistance is less than the smallest individual resistance.

Question 9

Given three resistors $R_1 = 12.5 \Omega$, $R_2 = 14.7 \Omega$ in series, connected in parallel to $R_3 = 7.5 \Omega$, and this combination in series with $R_4 = 10.3 \Omega$. If a $10.0 	ext{ V}$ battery is connected, what is the total resistance?

Accepted Answer

$R_{total} = R_4 + \left[ \dfrac{1}{\dfrac{1}{R_1 + R_2} + \dfrac{1}{R_3}} \right] = 10.3 + \dfrac{1}{\dfrac{1}{27.2} + \dfrac{1}{7.5}} \approx 15.1 \Omega$

Question 10

In a circuit, the sum of currents entering a junction is equal to the sum of currents leaving the junction. This is known as:

Accepted Answer

Kirchhoff's junction rule

Question 11

A capacitor of $18 	ext{ mF}$ is charged to $380 	ext{ mC}$ and then discharged through a $5.0 \Omega$ resistor. What is the time constant of the circuit?

Accepted Answer

$	au = RC = 5.0 \Omega 	imes 18 	imes 10^{-3} 	ext{ F} = 0.09 	ext{ s}$

Question 12

During the discharge of a capacitor, the charge on the plates at time $t$ is given by:

Accepted Answer

$Q = Q_0 e^{-t/RC}$

Question 13

If the potential difference across a discharging capacitor drops to one-quarter of its initial value, how much time has elapsed?

Accepted Answer

$t = RC \ln 4$

Question 14

Which of the following statements about the time constant $	au$ in an RC circuit is correct?

Accepted Answer

It is the time taken for the capacitor to reach 63% of its final charge during charging.

Question 15

Which of the following is true about the resistivity of metals as temperature increases?

Accepted Answer

Resistivity increases with increasing temperature.

Question 16

A battery supplies a potential difference $V$ to a circuit with internal resistance $r$ and external resistance $R$. What is the terminal voltage across the external resistor?

Accepted Answer

$V_{terminal} = E - Ir$

Question 17

In a series circuit, which quantity is the same for all resistors?

Accepted Answer

Current

Question 18

Which of the following is NOT a correct application of Ohm's law?

Accepted Answer

Across a non-ohmic device such as a diode

Current Electricity: Electric Charges in Motion

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