Direct-Current Circuits

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. It serves for direct current feed. E. Nothing electrical, it is for mechanical sturdiness.

C

Three resistors connected in parallel have the individual voltages labeled V1, V2 and V3, respectively. Which of the following expresses the total voltage VT across the three resistors when connected in this manner? A. VT = V1 + V2 + V3 B. VT = (1/V1 + 1/V2 + 1/V3) C. VT = V1 = V2 = V3 D. VT = (1/V1 + 1/V2 + 1/V3)-1 E. VT = 3V1 = 3V2 = 3V3

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 D. IT = (1/I1 + 1/I2 + 1/I3)-1 B. IT = (1/I1 + 1/I2 + 1/I3) E. IT = 3I1 = 3I2 = 3I3 C. IT = I1 = I2 = I3

C

Three 8.0- resistors are connected in series. What is their equivalent resistance? A. 24.0 D. 0.13 B. 8.0 E. 0.075 C. 0.38

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 E. IT = 3I1 = 3I2 = 3I3

A

Three resistors, each with resistance R1, are in series in a circuit. They are replaced by one equivalent resistor, R. Comparing this resistor to the first resistor of the initial circuit, which of the following 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 less than R1. E. R is equal to R1.

A

Which voltage is not caused by a source of emf? A. the voltage across a charged capacitor B. the voltage across two copper-iron junctions at different temperatures C. the voltage across the terminals of a dry cell battery D. the voltage from an electric generator E. None of the above choices is valid.

A

Household circuits are wired in ____. A. series C. both series and parallel B. 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 D. gravity-free insulator B. ground-fault interrupter E. guided fault isolation C. give fast interruption

B

The basic function of an electromotive force in a circuit is to do which of the following? A. Convert electrical energy into some other form. B. Convert some other form of energy into electrical. C. Both choices (a) and (b) are valid. D. None of the above choices are valid.

B

The two ends of a 3.0- resistor are connected to a 9.0-V battery. What is the total power delivered by the battery to the circuit? A. 3.0 W D. 0.11 W B. 27 W E. 0.067 W C. 0.33 W

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. E. R is less than R1.

B

Three resistors connected in series have individual voltages labeled V1, V2 and V3, respectively. Which of the following expresses the value of the total voltage VT taken over the three resistors together? A. VT = V1 + V2 + V3 D. VT = (1/V1 + 1/V2 + 1/V3)-1 B. VT = (1/V1 + 1/V2 + 1/V3) E. VT = 3V1 = 3V2 = 3V3 C. VT = V1 = V2 = V3

A

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. E. The answer depends on the internal resistance of the battery.

A

Three resistors with values of R1, R2 and R3, respectively, are connected in series. Which of the following expresses the total resistance, RT, of the three resistors? A. RT = R1 + R2 + R3 D. RT = (1/R1 + 1/R2 + 1/R3)-1 B. RT = (1/R1 + 1/R2 + 1/R3) E. RT = 3R1 = 3R2 = 3R3 C. RT = R1 = R2 = R3

A

The two ends of a 3.0- resistor are connected to a 9.0-V battery. What is the current through the resistor? A. 27 A D. 0.33 A B. 6.3 A E. 0.17 A C. 3.0 A

C

When a light bulb is turned on, its resistance increases until it reaches operating temperature. What happens to the current in the bulb as it is warming up? A. It stays constant. D. It increases at first and then decreases. B. It increases. E. It decreases at first and then increases. C. It decreases.

C

Three resistors with values R1, R2 and R3, respectively, are connected in parallel. Which of the following expresses the total resistance, RT, of the three resistors when connected in parallel? A. RT = R1 + R2 + R3 B. RT = (1/R1 + 1/R2 + 1/R3) C. RT = R1 = R2 = R3 D. RT = (1/R1 + 1/R2 + 1/R3)-1 E. RT = 3R1 = 3R2 = 3R3

D

Three resistors, with values of 2.0, 4.0 and 8.0 , respectively, are connected in series. What is the overall resistance of this combination? A. 0.58 D. 14.0 B. 1.1 E. 19.0 C. 7.0

D