Physics 112 HW #4
April 23, 2010
1. A cigarette lighter in a car is a resistor that, when activated, is connected across the 12-V battery. Suppose that a lighter uses 25.3 W of power. (a) Find the resistance of the lighter.
(b) Find the current that the battery delivers to the lighter.
2. A blow-dryer and a vacuum cleaner each operate with a voltage of 120 V. The current rating of the blow-dryer is 12 A, and that of the vacuum cleaner is 4.0 (a) Determine the power consumed by the blow-dryer.
A.
(b) Determine the power consumed by the vacuum cleaner.
(c) Determine the ratio of the energy used by the blow-dryer in 13 minutes to the energy used by the vacuum cleaner in one-half hour.
3. A 55.0-W lamp is placed in series with a resistor and a 120.0-V source. If the voltage across the lamp is 24 V, what is the resistance Rof the resistor?

Physics 112 HW #4
April 23, 2010