Physics Chapter 18 Direct Current Circuits

If R1 < R2 < R3,and if these resistors are connected in parallel in a circuit, which one has the highest current? a. R1 b. R2 c. R3 d. All have the same current.

A

In a loop in a closed circuit, the sum of the currents entering a junction equals the sum of the currents leaving the junction because .... a. charge in neither created nor destroyed at a junction. b. the potential of the nearest battery is the potential at the junction. c. there are no transformations of energy from one type to another in a circuit loop. d. capacitors tend to maintain current through them at a constant value. e. current is used up after it leaves the junction.

A

One common use for a capacitor is to supply the power for a flash. Why is this? a. The capacitor has a lower internal resistance than a battery and thus can supply more current to the flash. b. The capacitor can store more voltage than the battery. c. While it is possible to have a battery supply this current, it would break the battery. d. For a flash to work it needs charge. Charge is stored in capacitors and voltage is stored in batteries.

A

Resistors of values 8.0 W, 12.0 W, and 24.0 W are connected in parallel across a fresh battery. Which resistor dissipates the greatest power? a. the 8.0-W resistor b. the 12.0-W resistor c. the 24.0-W resistor d. All dissipate the same power when in parallel.

A

The circuit below contains three 100-watt light bulbs. The emf e = 110 V. Which light bulb(s) is(are) the brightest? a. A b. B c. C d. B and C e. All three are equally bright.

A

Three resistors connected in parallel each carry currents labeled I1, I2 and I3. Which of the following expresses the value of the total current IT in the combined system? a. IT = I1 + I2 + I3 b. IT = (1/I1 + 1/I2 + 1/I3) c. IT = I1 = I2 = I3 d. IT = (1/I1 + 1/I2 + 1/I3)-1

A

Three resistors connected in series have individual voltages labeled DV1, DV2 and DV3, respectively. Which of the following expresses the value of the total voltage DVT taken over the three resistors together? a. DVT = DV1 + DV2 + DV3 b. DVT = (1/DV1 + 1/DV2 + 1/DV3) c. DVT = DV1 = DV2 = DV3 d. DVT = (1/DV1 + 1/DV2 + 1/DV3)-1

A

Which one of these statements is true about internal resistance? a. All batteries have internal resistance, but can be treated as perfect batteries in series with an internal resistor. b. All batteries have internal resistance, but can be treated as perfect batteries in parallel with an internal resistor. c. All batteries have internal resistance, but the internal resistor can be removed to make the battery perfect. d. Only cheap batteries have internal resistance.

A

Household circuits are wired in ________. a. series b. parallel c. both series and parallel d. neither series nor parallel

B

In applications where electrical shocks may be more likely, such as around water in kitchens and bathrooms, special outlets called GFI's are used. What does GFI stand for? a. get free instantly b. ground-fault interrupter c. give fast interruption d. gravity-free insulator

B

The circuit below contains 4 100-W light bulbs. The emf is 110 V. Which light bulb(s) is(are) brightest? a. A b. B c. C d. D e. C and D

B

The circuit below contains three 100-W light bulbs and a capacitor. The emf is 110 V and the capacitor is fully charged. Which light bulb(s) is(are) brightest? a. A b. B c. C d. A and B e. A and C

B

Three resistors, each of different value, are used in a circuit with a power source supplying 12 volts. For which of the following resistor combinations is the total power supplied the greatest? a. all three resistors in series b. all three resistors in parallel c. two of the resistors in parallel with the third resistor in series with the parallel pair d. This cannot be found until it is known which resistor is in series with the parallel pair.

B

Three resistors, each with resistance R1, are in parallel in a circuit. They are replaced by one equivalent resistor, R. Compare this resistor to the first resistor of the initial circuit. Which of the following statements is true? a. The current through R equals the current through R1. b. The voltage across R equals the voltage across R1. c. The power given off by R equals the power given off by R1. d. R is greater than R1.

B

Which two resistors are in parallel with each other? a. R and R4 b. R2 and R3 c. R2 and R4 d. R and R1

B

Household 120-V outlets are made to accept three-pronged plugs. One of the prongs attaches to the "live" wire at 120 V, and another attaches to the "neutral" wire that is connected to ground. What is the round third prong for? a. It serves as a backup to the hot wire. b. It lets the appliance run if the neutral wire breaks. c. It connects the case of the appliance directly to ground for safety purposes. d. Nothing electrical, it is for mechanical sturdiness

C

Resistors of values 8.0 W, 12.0 W, and 24.0 W are connected in series across a battery with a small internal resistance. Which resistor dissipates the greatest power? a. the 8.0-W resistor b. the 12.0-W resistor c. the 24.0-W resistor d. The answer depends on the internal resistance of the battery.

C

The battery is disconnected from a series RC circuit after the capacitor is fully charged and is replaced by an open switch. When the switch is closed, a. the current through the resistor is always greater than the current through the capacitor. b. the current through the resistor is always less than the current through the capacitor. c. the current through the resistor is always equal to the current through the capacitor. d. the capacitor does not allow current to pass. e. the current stops in the resistor.

C

The capacitor in the circuit below has a very large capacitance and is initially uncharged. After the switch is closed, what happens to the light bulb? Circuit with switch, light bulb, and capacitor. a. It never glows because the capacitor represents an open in the circuit. b. It glows only after the capacitor is fully charged. c. It glows for a short time as the capacitor is being charged. d. It glows continuously e. It glows intermediately

C

The circuit below contains three resistors, A, B, and C, which all have equal resistances. The emf e = 110V. Which resistor generates the most thermal energy after the switch is closed? a. A b. B c. C d. A and B e. All three generate equal amounts of thermal energy.

C

Three resistors connected in parallel have the individual voltages labeled DV1, DV2 and DV3, respectively. Which of the following expresses the total voltage DVT across the three resistors when connected in this manner? a. DVT = DV1 + DV2 + DV3 b. DVT = (1/DV1 + 1/DV2 + 1/DV3) c. DVT = DV1 = DV2 = DV3 d. DVT = (1/DV1 + 1/DV2 + 1/DV3)-1

C

Three resistors connected in series each carry currents labeled I1, I2 and I3. Which of the following expresses the value of the total current IT in the system made up of the three resistors in series? a. IT = I1 + I2 + I3 b. IT = (1/I1 + 1/I2 + 1/I3) c. IT = I1 = I2 = I3 d. IT = (1/I1 + 1/I2 + 1/I3)-1

C

A series circuit consists of a 100 V DC power source, a 100 W resistor, and a variable resistor of resistance R, which varies from 0 to 100 W. The current in the circuit is a. directly proportional to R. b. inversely proportional to R. c. directly proportional to (100 W + R). d. inversely proportional to (100 W + R). e. neither directly nor inversely proportional to R or to (100 W + R).

D

A very large resistor is in parallel with a very small resistor. The equivalent resistance of this combination will be.... a. slightly greater than the resistance of the large resistor. b. slightly less than the resistance of the large resistor. c. slightly greater than the resistance of the small resistor. d. slightly less than the resistance of the small resistor.

D

Given the circuit below. How many of Kirchhoff's equations need to be written to solve for the currents in each branch? Circuit with 4 parallel paths a. 1 b. 2 c. 3 d. 4 e. 5

D

In an RC circuit using two capacitors in series with two resistors, which of the following combinations would give the greatest time constant? a. both capacitors in series placed in series with both resistors in series b. both capacitors in parallel placed in series with both resistors in parallel c. both capacitors in series placed in series with both resistors in parallel d. both capacitors in parallel placed in series with both resistors in series

D

The circuit below contains 3 100-W light bulbs and a capacitor. The emf is 110 V. Which light bulb(s) is(are) brightest? (Assume the capacitor is fully charged.) a. A b. B c. C d. A and B e. All three are equally bright.

D

When a battery has internal resistance, some energy is lost. What happens to the lost energy? a. The lost energy isn't really lost at all; it's all comes down to poor design in the circuit. b. It corrodes away the internal resistor. c. It is stored in the battery as lost energy. d. It is lost in heating up the battery

D

Which resistor is in series with resistor R? a. R1 b. R2 c. R3 d. R4

D

The circuit below contains 5 identical light bulbs. The emf is 110 V. Which light bulb(s) is(are) brightest? a. A: The one closest to the positive terminal of the battery. b. A and C: The bulbs closest to the positive terminal of the battery. c. A and B: Because they are closest to the terminals of the battery. d. C and D: Because they receive current from A and B and from E. e. E: Because the potential difference across E is that of the battery.

E