1. A voltmeter connected across the terminals of a tungsten-filament light bulb measures 117 V when an ammeter in line with the bulb registers a current of 0.513 A.

HINT

(a)Find the resistance of the light bulb. (Enter your answer in ohms.)

(b)Find the resistivity of tungsten (in m) at the bulb's operating temperature if the filament has an uncoiled length of 0.593 m and a radius of 2.43 10⁵ m. m

2. The potential difference across a resting neuron in the human body is about 81.0 mV and carries a current of about 0.260 mA. How much power does the neuron release?

3. A typical cellular phone consumes an average of about 1.34 W of electrical power and operates on 3.80 V.

HINT

(a)What average current (in A) does the phone draw from its battery? A

(b)Calculate the energy (in J) stored in a fully charged battery if the phone requires charging after 7.03 hours. J

4. If electrical energy costs $0.12 per kilowatt-hour, how much does the cost of the following event? (a) To burn a 100-W lightbulb for 24 h. $ (b) To operate an electric oven for 4.6 h if it carries a current of 20.0 A at 220 V. $

5. A portable coffee heater supplies a potential difference of 12.0 V across a Nichrome heating element with a resistance of 1.92 .

HINT

(a)Calculate the power (in W) consumed by the heater. W(b)How many minutes would it take to heat 1.13 kg of coffee from 22.1C to 47.2C with this heater? Coffee has a specific heat of

4184

J

(kg C)

.

Neglect any energy losses to the environment. min