Conceptual Physics

For part (b), calculate the cost per kW·h.

This is less than the predicted cost of electricity from the utility company, so the school will save money in electricity costs if they install the solar panels. Even better, by using renewable energy they will contribute to a less polluted future. On the web, you can find out more about solar energy and find out the average insolation anywhere in the world.

Step Reason

5. convert to kW·h

6. c = C/E cost per kW·h

7. enter values

25.9 - Interactive checkpoint: running a dishwasher

Suppose you measure the current

flow to a dishwasher and find that the

average current is 9.50 A over the

45.0-minute dishwasher cycle. The

dishwasher is powered by a potential

difference of 120 V. If electricity costs

$0.0900 per kilowatt-hour, what is the

cost of running one dishwasher load?

Answer:

p = $ per dishwasher cycle

25.10 - Sample problem: using a hair dryer

Here, you will treat the hair dryer as though it were a direct current (DC) appliance.

Variables

The label on an electric blow dryer

says it uses 1100 W and is designed

for 120 V outlets. How much current

flows through the hair dryer? What is

its resistance?

power rating P = 1100 W

potential difference ǻV = 120 V

current I

resistance R