Q: A flashlight uses a battery to power its bulb. If the battery has an emf of 1.5 V and the bulb has a resistance of 3 Ω, what is the current flowing through the bulb, assuming the internal resistance of the battery is negligible?

$$I = \frac{V}{R} = \frac{1.5}{3} = 0.5\ \text{A}$$

Q: If a light bulb is connected to a battery and the current is 2 A, the bulb’s resistance is 6 Ω, and the battery’s internal resistance is 1 Ω, what is the emf of the battery?

$$\mathcal{E} = I(R + r) = 2 \times (6 + 1) = 14\ \text{V}$$

Question 1

A flashlight uses a battery to power its bulb. If the battery has an emf of 1.5 V and the bulb has a resistance of 3 Ω, what is the current flowing through the bulb, assuming the internal resistance of the battery is negligible?

Accepted Answer

$$I = \frac{V}{R} = \frac{1.5}{3} = 0.5\ 	ext{A}$$

Question 2

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

Accepted Answer

Conventional current flows in the direction that positive charges would move.

Question 3

In an ionic solution, such as sodium chloride dissolved in water, how is the total current calculated?

Accepted Answer

By adding the currents due to each kind of charged particle.

Question 4

A copper wire has a length $$L$$ and cross-sectional area $$A. $$Its resistance $$R is $$given by which formula?

Accepted Answer

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

Question 5

The resistivity of a metal at temperature $$T is $$given by $$\rho(T) = \$$rho_0$$ [1 + \alpha (T - T_0$)]. $$What does $$\alpha$$ represent?

Accepted Answer

The temperature coefficient of resistivity.

Question 6

Which material shows a sudden drop to zero resistivity below a critical temperature $$T_c$$?

Accepted Answer

Superconductor

Question 7

A circuit board has copper traces printed on an insulating substrate. Why does current not flow between the traces?

Accepted Answer

The substrate has a very high resistivity.

Question 8

A resistor obeys Ohm’s law. What is the relationship between current $$I$$ and voltage $$V$$?

Accepted Answer

$$V = IR$$

Question 9

A semiconductor diode is a nonohmic resistor. Which graph best represents its current-voltage relationship?

Accepted Answer

Current increases nonlinearly with voltage in one direction, and little current flows in the opposite direction.

Question 10

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

Accepted Answer

$$V_{ab} = \mathcal{E} - Ir$$

Question 11

If a light bulb is connected to a battery and the current is 2 A, the bulb’s resistance is 6 Ω, and the battery’s internal resistance is 1 Ω, what is the emf of the battery?

Accepted Answer

$$\mathcal{E} = I(R + r) = 2 	imes (6 + 1) = 14\ 	ext{V}$$

Question 12

Which of the following best describes the power delivered to a circuit element?

Accepted Answer

$$P = V_{ab} I$$

Question 13

A metallic conductor’s resistivity increases with temperature. Which equation models this behavior?

Accepted Answer

$$\rho(T) = \$$rho_0$$ [1 + \alpha (T - T_0$)]$$

Question 14

Which device in a circuit diagram is used to measure the potential difference between two points?

Accepted Answer

Voltmeter

Question 15

A thermistor is used as a thermometer. What property of semiconductors makes this possible?

Accepted Answer

Resistivity decreases with increasing temperature.

Question 16

Which of the following statements about energy in a circuit is correct?

Accepted Answer

The energy of the charges decreases as current flows through a resistor.

Question 17

In a metallic conductor, what is the physical mechanism for resistance?

Accepted Answer

Electrons collide with stationary positive ions in the crystal.

Question 18

A resistor has color bands: green, violet, orange, and silver. What is its resistance and tolerance?

Accepted Answer

$$57\ 	ext{k}\Omega$$ with $$\pm 10\%$$ tolerance

Question 19

Which of the following is NOT a property of a source of electromotive force (emf)?

Accepted Answer

It is a force that pushes charges through a circuit.

Current, Resistance, and Electromotive Force: Study Notes

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