Q: In a circuit, if the current through a $$25\,\Omega$$ resistor is $$0.11\,\mathrm{A}$$, what is the voltage drop across the resistor?

$$V = 0.11 \times 25 = 2.75\,\mathrm{V}$$

Q: A $$9.0\,\mathrm{V}$$ battery supplies $$360\,\mathrm{mA} to a $$resistor. What is the power dissipated in the resistor?

$$P = 0.360 \times 9.0 = 3.24\,\mathrm{W}$$

Q: What is the time constant $$\tau of an RC $$circuit, and what does it physically represent?

$$\tau = RC$$, the time for current to decrease to $$1/e of $$its initial value

Question 1

A real battery is modeled as an ideal voltage source $$V in $$series with an internal resistance $$r. If a $$load resistor $$R_L is $$connected across the battery, what is the voltage $$V_L$$ across the load resistor?

Accepted Answer

$$V_L = V \frac{R_L}{r + R_L}$$

Question 2

In the circuit shown with a battery of emf $$\mathcal{E}$$ and internal resistance $$r$$, and a load resistor $$R_L$$, what happens to the voltage across $$R_L as$$ $$r$$ increases significantly?

Accepted Answer

The voltage across $$R_L$$ decreases and approaches zero.

Question 3

A voltmeter should be connected in which way in a circuit to measure the potential difference across a component?

Accepted Answer

In parallel with the component

Question 4

Given a battery with emf $$\mathcal{E} = 12\,\mathrm{V}$$ and internal resistance $$r = 1\,\Omega$$, connected to a $$5\,\Omega$$ resistor, what is the current in the circuit?

Accepted Answer

$$I = \frac{12}{5 + 1} = 2.0\,\mathrm{A}$$

Question 5

Which equation correctly expresses the power dissipated in a resistor $$R$$ when a current $$I$$ flows through it?

Accepted Answer

$$P = I^2$ R$$

Question 6

A $$1.5\,\mathrm{V}$$ battery is connected to a $$20\,\Omega$$ light bulb. What is the power dissipated in the bulb?

Accepted Answer

$$P = \frac{(1.5)^2$}{20} = 0.113\,\mathrm{W}$$

Question 7

In a circuit, if the current through a $$25\,\Omega$$ resistor is $$0.11\,\mathrm{A}$$, what is the voltage drop across the resistor?

Accepted Answer

$$V = 0.11 	imes 25 = 2.75\,\mathrm{V}$$

Question 8

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

Accepted Answer

It measures the current and must be connected in series.

Question 9

A real battery has an emf $$\mathcal{E}$$ and internal resistance $$r. If $$the battery is short-circuited (terminals connected with a wire of negligible resistance), what is the current?

Accepted Answer

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

Question 10

In the context of Kirchhoff’s Loop Rule, what is the algebraic sum of the changes in potential around any closed loop in a circuit?

Accepted Answer

$$\sum \Delta V = 0$$

Question 11

A $$9.0\,\mathrm{V}$$ battery supplies $$360\,\mathrm{mA} to a $$resistor. What is the power dissipated in the resistor?

Accepted Answer

$$P = 0.360 	imes 9.0 = 3.24\,\mathrm{W}$$

Question 12

Which equation correctly gives the voltage at point $$b$$ relative to $$a$$ for a resistor $$R$$ with current $$I$$ flowing from $$a to$$ $$b$$?

Accepted Answer

$$V_b = V_a - IR$$

Question 13

In an RC circuit, the current as a function of time after closing the switch is given by which equation?

Accepted Answer

$$I(t) = \frac{\mathcal{E}}{R} e$$^{-t/RC}$$

Question 14

What is the time constant $$	au of an RC $$circuit, and what does it physically represent?

Accepted Answer

$$	au = RC$$, the time for current to decrease to $$1/e of $$its initial value

Question 15

A capacitor $$C is $$charged through a resistor $$R by a $$battery of emf $$\mathcal{E}. $$What is the charge on the capacitor at time $$t$$?

Accepted Answer

$$Q(t) = C \mathcal{E} (1 - e$$^{-t/RC}$$)$$

Question 16

If a voltmeter is connected across a resistor in a circuit, what does it measure?

Accepted Answer

The potential difference (voltage) across the resistor

Question 17

In a multi-loop circuit, if you assign a current direction and calculate a negative value for the current, what does this mean?

Accepted Answer

The actual current flows in the opposite direction to your assumption.

Question 18

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.

DC Circuits, Batteries, and RC Circuits: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards