Q: A resistor has color bands: red, violet, yellow, and gold. What is its resistance and tolerance?

$$27 \times 10^4$\ \Omega$$ with $$\pm 5\%$$ tolerance

Question 1

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

Accepted Answer

The direction in which positive charges would move.

Question 2

A copper wire has a cross-sectional area $$A$$ and carries a current $$I. If $$the number density of free electrons is $$n$$ and the charge of an electron is $$e$$, what is the drift velocity $$v_d of $$the electrons?

Accepted Answer

$$v_d = \frac{I}{n e A}$$

Question 3

A patient receives a current of $$25\ \mu\mathrm{A}$$ through the heart, which has a resistance of $$250\ \Omega. $$What is the voltage across the heart?

Accepted Answer

$$V = 6.25\ \mathrm{mV}$$

Question 4

Which of the following statements about Ohm's Law is correct?

Accepted Answer

Ohm's Law states that $$V = IR$$ for materials where the resistance $$R is $$constant over a range of voltages.

Question 5

A resistor has color bands: red, violet, yellow, and gold. What is its resistance and tolerance?

Accepted Answer

$$27 	imes 10^4$\ \Omega$$ with $$\pm 5\%$$ tolerance

Question 6

Which material would you expect to have the lowest resistivity at room temperature?

Accepted Answer

Silver

Question 7

A battery with emf $$\mathcal{E}$$ and internal resistance $$r is $$connected to an external resistor $$R. $$What is the current in the circuit?

Accepted Answer

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

Question 8

Which of the following best describes the function of a voltmeter in a circuit?

Accepted Answer

It measures the potential difference between two points and is connected in parallel.

Question 9

Three resistors, $$R_1 = 2$$\ \Omega$$, R_2$ = 3\ \Omega$$, and $$R_3 = 6$$\ \Omega$$, are connected in parallel. What is the equivalent resistance?

Accepted Answer

$$R_{eq} = 1\ \Omega$$

Question 10

A 12 V car battery is used to power a 48 W headlight. What is the current through the headlight?

Accepted Answer

$$I = 4\ \mathrm{A}$$

Question 11

Which of the following is a correct application of Kirchhoff's junction rule?

Accepted Answer

The sum of currents entering a junction equals the sum of currents leaving the junction.

Question 12

A circuit contains a $$6\ \Omega$$ resistor in series with a parallel combination of two $$3\ \Omega$$ resistors. What is the total resistance?

Accepted Answer

$$R_{total} = 7.5\ \Omega$$

Question 13

Which of the following statements about resistors in series is correct?

Accepted Answer

The total resistance is the sum of the individual resistances.

Question 14

A camera flash uses an RC circuit to store energy. If the resistance is doubled while the capacitance remains the same, what happens to the time constant $$	au$$?

Accepted Answer

$$	au$$ doubles

Question 15

Which of the following best explains why metals have lower resistivity than insulators?

Accepted Answer

Metals have a higher density of free charge carriers.

Question 16

A rechargeable battery is being charged by connecting it in series with another battery and a resistor. Which of the following is true about the direction of current?

Accepted Answer

The current flows into the positive terminal of the battery being charged.

Question 17

If a voltmeter is connected across a resistor in a circuit, what property should the voltmeter have to minimize its effect on the circuit?

Accepted Answer

Very high resistance

Question 18

A wire of length $$L$$ and cross-sectional area $$A is $$made of a material with resistivity $$\rho. $$What is the resistance $$R of $$the wire?

Accepted Answer

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

Question 19

In a circuit, if the power dissipated by a resistor is $$P$$ and the current through it is $$I$$, what is the voltage across the resistor?

Accepted Answer

$$V = \frac{P}{I}$$

Current, Resistance, and Directed-Current Circuits (Chapter 19 Study Notes)

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