Question 1

A copper wire has a length of 1.5 m and a diameter of 3.2 mm. Given the resistivity of copper is $$ho_{Cu} = 1.72 	imes 10$$^{-8}$$ \, \Omega \cdot m$$, what is the resistance of the wire?

Accepted Answer

$$R = 0.255 \, m\Omega$$

Question 2

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

Accepted Answer

It is the direction that positive charges would move through the conductor.

Question 3

A $$6.0 \, \Omega$$ resistor is connected to a $$24 \, V$$ emf source. What is the current passing through the resistor?

Accepted Answer

$$I = 4.0 \, A$$

Question 4

Which equation correctly relates resistance, resistivity, length, and cross-sectional area of a wire?

Accepted Answer

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

Question 5

If the temperature of a metal wire increases, what happens to its resistivity?

Accepted Answer

It increases.

Question 6

A battery with emf $$\mathcal{E} = 12 \, V$$ and internal resistance $$r = 2 \, \Omega is $$connected to a $$4 \, \Omega$$ resistor. What is the current in the circuit?

Accepted Answer

$$I = 2 \, A$$

Question 7

Which of the following is the correct expression for Ohm’s Law?

Accepted Answer

$$V = IR$$

Question 8

A light bulb rated at $$60 \, W is $$connected to a $$120 \, V$$ outlet. What is the resistance of the bulb when operating?

Accepted Answer

$$R = 240 \, \Omega$$

Question 9

Which material would have the lowest resistance for a wire of identical dimensions at room temperature?

Accepted Answer

Silver

Question 10

A superconductor is cooled below its critical temperature $$T_c. $$What happens to its resistivity?

Accepted Answer

It drops to zero.

Question 11

A $$12 \, V$$ battery with $$2 \, \Omega$$ internal resistance is connected to a $$4 \, \Omega$$ resistor. What is the voltage drop across the $$4 \, \Omega$$ resistor?

Accepted Answer

$$8 \, V$$

Question 12

Which of the following best describes the function of an emf source in a circuit?

Accepted Answer

It supplies energy to move charges from lower to higher potential.

Question 13

If a wire’s length is doubled and its cross-sectional area is halved, by what factor does its resistance change?

Accepted Answer

It becomes four times greater.

Question 14

Which of the following is the correct formula for the temperature dependence of resistance?

Accepted Answer

$$R = R_0$ [1 + \alpha (T - T_0$)]$$

Question 15

A voltmeter is connected across a resistor in a circuit. What does it measure?

Accepted Answer

The potential difference across the resistor.

Question 16

Which of the following statements about internal resistance is correct?

Accepted Answer

It causes a voltage drop inside the battery.

Question 17

A $$12 \, V$$ battery with $$2 \, \Omega$$ internal resistance is connected in series with a $$4 \, \Omega$$ resistor. What is the total power dissipated in the circuit?

Accepted Answer

$$16 \, W$$

Question 18

Which of the following is a correct statement about the SI unit of current?

Accepted Answer

It is the ampere, which is a coulomb per second.

Question 19

A circuit contains a battery with emf $$\mathcal{E}$$, internal resistance $$r$$, and an external resistor $$R. $$Which equation gives the current in the circuit?

Accepted Answer

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

Chapter 19: Current, Resistance, and DC Circuits – Study Notes

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