Q: A battery with emf $$\varepsilon$$ and internal resistance $$r is $$connected to a load resistor $$R_{\text{load}}. $$What is the expression for the current $$I in $$the circuit?

$$I = \frac{\varepsilon}{R_{\text{load}} + r}$$

Question 1

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

Accepted Answer

$$2\ \mathrm{V}$$

Question 2

Which equation correctly relates the terminal voltage $$V of a $$real battery to its emf $$\varepsilon$$, internal resistance $$r$$, and current $$I$$?

Accepted Answer

$$V = \varepsilon - Ir$$

Question 3

A platinum wire has a resistance of $$11\ \Omega at$$ $$20^\circ \mathrm{C}. If $$the temperature coefficient of resistivity is $$\alpha = 3.93 	imes 10$$^{-3}$$\ ^\circ \mathrm{C}^{-1}$$, what is its resistance at $$1000^\circ \mathrm{C}$$?

Accepted Answer

$$53\ \Omega$$

Question 4

Which of the following best describes the difference between an ideal and a real emf device?

Accepted Answer

An ideal emf device has zero internal resistance, while a real emf device has nonzero internal resistance.

Question 5

If a voltmeter is connected across the terminals of a battery supplying current to a load, what does it measure?

Accepted Answer

The terminal voltage, which is less than the emf if current is flowing

Question 6

A battery with emf $$\varepsilon$$ and internal resistance $$r is $$connected to a load resistor $$R_{	ext{load}}. $$What is the expression for the current $$I in $$the circuit?

Accepted Answer

$$I = \frac{\varepsilon}{R_{	ext{load}} + r}$$

Question 7

Which of the following statements about electric current is correct?

Accepted Answer

Current is the rate at which charge flows through a point in a circuit.

Question 8

A battery with emf $$\varepsilon = 9\ \mathrm{V}$$ and internal resistance $$r = 1\ \Omega is $$connected to a $$8\ \Omega$$ resistor. What is the terminal voltage across the battery?

Accepted Answer

$$8.1\ \mathrm{V}$$

Question 9

Which of the following best explains why the terminal voltage of a battery decreases as the current increases?

Accepted Answer

The internal resistance causes a larger voltage drop as current increases.

Question 10

A coil of platinum wire has a diameter of $$0.5\ \mathrm{mm}$$ and a length of $$20\ \mathrm{m}. $$The resistivity of platinum at $$20^\circ \mathrm{C} is$$ $$1.1 	imes 10$$^{-7}$$\ \Omega\cdot\mathrm{m}. $$What is the resistance of the wire at $$20^\circ \mathrm{C}$$?

Accepted Answer

$$11\ \Omega$$

Question 11

Which of the following is the correct SI unit for electromotive force (emf)?

Accepted Answer

Volt (V)

Question 12

If the potential difference across a resistor is $$6\ \mathrm{V}$$ and the current through it is $$2\ \mathrm{A}$$, what is the resistance?

Accepted Answer

$$3\ \Omega$$

Question 13

A battery is connected to a resistor and an ammeter as shown in the circuit. If the ammeter reads $$2\ \mathrm{A}$$ and the resistor is $$4\ \Omega$$, what is the terminal voltage of the battery?

Accepted Answer

$$8\ \mathrm{V}$$

Question 14

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

Accepted Answer

It measures the current through a component.

Question 15

A battery with emf $$\varepsilon$$ and internal resistance $$r is $$connected to a load resistor $$R_{	ext{load}}. If$$ $$R_{	ext{load}} is $$much larger than $$r$$, what can be said about the terminal voltage?

Accepted Answer

It is approximately equal to the emf.

Question 16

Which of the following is the correct expression for the average electric current?

Accepted Answer

$$I_{av} = \frac{\Delta Q}{\Delta t}$$

Question 17

A battery with emf $$\varepsilon = 6\ \mathrm{V}$$ and internal resistance $$r = 0.5\ \Omega is $$connected to a $$5.5\ \Omega$$ resistor. What is the power dissipated in the resistor?

Accepted Answer

$$5.45\ \mathrm{W}$$

Question 18

Which of the following is true about the potential changes around a closed circuit?

Accepted Answer

The net change in potential energy is zero.

Question 19

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

Accepted Answer

The voltage across the resistor

Week 4 Lec. 3

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