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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