Q: A copper wire has a cross-sectional area of $$8.2 \times 10$$^{-7}$$ \text{ m}^2$$ and carries a current of 1.67 A. What is the current density in the wire?

$$2.04 \times 10$$^{6}$$ \text{ A/m}^2$$

Q: A copper wire has a resistance of 1.00 $$\Omega at$$ $$20^\circC. $$What is its resistance at $$100^\circC$$? (Temperature coefficient $$\alpha = 0.00393/ ^\circC)$$

$$R = 1.00 \Omega \times [1 + 0.00393 \times (100 - 20)] = 1.314 \Omega$$

Question 1

A flashlight uses a battery to power a bulb. If the current flowing out of the battery is 0.5 A, what is the current flowing into the bulb?

Accepted Answer

0.5 A

Question 2

Which equation correctly defines electric current?

Accepted Answer

$$I = \frac{dQ}{dt}$$

Question 3

In a metallic conductor, the moving charges are electrons. What is the direction of conventional current?

Accepted Answer

In the direction positive charges would flow

Question 4

A wire carries a current of 2.0 A for 5.0 seconds. How much charge passes through the wire in this time?

Accepted Answer

10 C

Question 5

Which of the following best describes the drift speed of electrons in a metal wire when a constant electric field is applied?

Accepted Answer

Much slower than their random thermal speed

Question 6

The current density $$J in a $$wire is given by which of the following equations?

Accepted Answer

$$J = n q v_d$$

Question 7

A copper wire has a cross-sectional area of $$8.2 	imes 10$$^{-7}$$ 	ext{ m}^2$$ and carries a current of 1.67 A. What is the current density in the wire?

Accepted Answer

$$2.04 	imes 10$$^{6}$$ 	ext{ A/m}^2$$

Question 8

Which statement about resistivity is correct?

Accepted Answer

Resistivity is the ratio of the electric field in a material to the current density it causes

Question 9

The resistance $$R of a $$wire is given by which formula?

Accepted Answer

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

Question 10

A copper wire has a resistance of 1.00 $$\Omega at$$ $$20^\circC. $$What is its resistance at $$100^\circC$$? (Temperature coefficient $$\alpha = 0.00393/ ^\circC)$$

Accepted Answer

$$R = 1.00 \Omega 	imes [1 + 0.00393 	imes (100 - 20)] = 1.314 \Omega$$

Question 11

Which of the following materials exhibits a decrease in resistivity with increasing temperature?

Accepted Answer

Graphite (a semiconductor)

Question 12

What happens to the resistivity of a superconductor when cooled below its critical temperature?

Accepted Answer

It drops abruptly to zero

Question 13

A battery with emf $$\mathcal{E}$$ and internal resistance $$r is $$connected to a resistor $$R. $$What is the terminal voltage $$V_{term}$$ across the battery?

Accepted Answer

$$V_{term} = \mathcal{E} - I r$$

Question 14

Which device should be connected in parallel with the circuit element being measured and have infinite resistance?

Accepted Answer

An ideal voltmeter

Question 15

Which device should be connected in series with the circuit element being measured and have zero resistance?

Accepted Answer

An ideal ammeter

Question 16

If two copper wires of different diameters are joined end to end and current flows through them, what happens to the drift speed of electrons as they move from the larger-diameter wire into the smaller-diameter wire?

Accepted Answer

The drift speed increases

Question 17

A source of emf is connected by wires to a resistor, and electrons flow in the circuit. Compared to the potential energy of an electron before entering the resistor, the potential energy after leaving the resistor is:

Accepted Answer

Less

Question 18

Which of the following is true for an ohmic resistor?

Accepted Answer

Current is proportional to voltage at a given temperature

Question 19

A battery does 1.5 J of work on every coulomb of charge that passes through it. What is the emf of the battery?

Accepted Answer

1.5 V

Question 20

The power delivered to a circuit element is given by which equation?

Accepted Answer

$$P = V I$$

Chapter 25: Current, Resistance, and Electromotive Force – Study Notes

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