PHY: Chapter 13

E11. Three resistors of 3 Ω, 6 Ω, and 2 Ω are connected in parallel with one another. What is the equivalent resistance of this combination?

1 Ω

E5. A current of 0.6 A flows through a resistor with a voltage difference of 120 V across it. What is the resistance of this resistor?

200 Ohms

E1. A charge of 30 C passes at a steady rate through a resistor in a time of 5 s. What is the current through the resistor?

6 A

E13. A 6-V battery in a simple circuit produces a current of 1.5 A through the circuit. How much power is being delivered by the battery?

9 W

*Q9. Two circuit diagrams are shown. Which one, if either, will cause the lightbulb to light? Explain your analysis of each case.

Diagram B will allow the light bulb to light, since there is a closed circuit providing current from the battery through the bulb. Whether the switch is open or closed is immaterial here since it is in parallel with another conductor. In diagram A no potential difference is in the closed circuit since everything is connected to the positive terminal.

*Q27. Does a battery connected to an electric motor represent a perpetual-motion machine (see chapter 11)? Explain.

No. A battery is based on a chemical reaction that creates a potential difference as a side effect. When the reaction is complete there will be no more potential difference being generated.

Q3. In a simple battery-and-bulb circuit, is the electric current that enters the bulb on the side nearer to the positive terminal of the battery larger than the current that leaves the bulb on the opposite side? Explain.

No. The current flowing around a single loop circuit is the same at every point in the loop. Unless charge is leaking out or building up somewhere, the current is conserved.

Q21. In the circuit shown, the circle with an A in it represents an ammeter. Which of these statements is correct? Comment on each. a. The meter is in the correct position for measuring the current through R. b. No current will flow through the meter, so it will have no effect. c. The meter will draw a significant current from the battery.

The answer is c. An ammeter is a low-resistance device and is to be placed in series in the circuit, just as a flow meter is placed in a fluid circuit.

Q33. Why does a bimetallic strip bend when the temperature changes? Explain. (See everyday phenomenon box 13.2.)

The two types of metal have different rates of expansion when heated. Since the two metals are bonded together, the strip must bend to compensate for the greater length of one side.

E9. Three resistors are connected to a 6-V battery as shown. The internal resistance of the battery is negligible. a. What is the current through the 15-Ω resistance? b. Does this same current flow through the 25-Ω resistance? c. What is the voltage difference across the 20-Ω resistance?

a. 0.1 A b. yes c. 2 V

Q15. Two resistors are connected in series with a battery as shown in the diagram. R1 is less than R2. a. Which of the two resistors, if either, has the greater current flowing through it? Explain. b. Which of the two resistors, if either, has the greatest voltage difference across it? Explain.

a. The current is the same in each, since it is a series circuit. b. The voltage difference is greater across R2. According to Ohm's Law, V = I × R, so for the same current, the larger the resistance, the greater the potential difference.

E7. A 40-Ω resistor and a 60-Ω resistor are connected in series to a 12-V battery. a. What is the current flowing through each resistor? b. What is the voltage difference across each resistor?

a. 0.12 A b. 4.8, 7.2 V