Name: ______Period:______

PHYSICS: Energy and Power Lab

You have already learned how to calculate 3 electrical quantities: voltage, current, and resistance. Now you will practice calculatinga fourth quantity, power. You will find the power ratings of electrical appliances and use this information to estimate electrical costs.

Pre-lab questions

Use your notes and formula chart to answer the following questions.

  1. What is meant by “power rating” when referring to a common household appliance?
  1. How many joules of energy will a 60-watt light bulb use every second? In one minute? (2 different questions / problems here!)
  1. What is the formula for calculating power? Identify all symbols in the equation and list the units.
  1. How do you get more power when you need it?
  1. When current flows through a wire, part of the energy is transformed into heat. More current means more heat. How can you allow more current flow through a wire without making more heat?

Procedure:

Read the following carefully.

  1. Choose 7 devices commonly used in your home that are rated in KILOWATTS on the cards provided and list them in Table 1A. (Blue marks)
  1. Estimate the number of hours the device is used each month – take an average based on your group members. Assume that one month equals 30 days. If your coffee maker is used for a half hour each morning, you would calculate one-half hour times 30 days equals 15 hours per month.
  1. Multiply the power rating in kilowatts (from the second column) by the number of hours the appliance is used each month. If you use a 1-kilowatt toaster for five hours a month, you would multiply 1 times 5 and enter the answer in the column titled “Number kWh per month.”
  1. Calculate the amount of money your household spends to operate each appliance during one month. (Multiply the kilowatt-hours per month by the price per kilowatt-hour in order to determine your cost.)
  1. Now choose 7 devices commonly used in your home that are rated in WATTS on the cards provided and list them in Table 1B. (orange marks)
  1. Estimate the number of hours the device is used each month and record your answer in the column provided.
  1. Convert this time in HOURS to time in SECONDS and record your answer.
  1. Using the formula, E = Pt, calculate the energy used in Joules and record your answer.
  1. Use the conversion 1kWh = 3.6 x 106 J to convert the ENERGY IN JOULES to kilowatt-hours and record your answer.
  1. Calculate the amount of money your household spends to operate each appliance during one month and record your answers.

Data Analysis:

In the table below…

  • List the three appliances from your group that had the highest power ratings.
  • Then, think about the function of each appliance listed. What kind of work is being done? In other words, electrical energy is converted into what other type(s) of energy? Record your answer in the table.

Appliance / Power Rating in Kilowatts / Electrical energy converted to what kind of energy

Do you see any similarities in the kinds of work being done by the three appliances you listed in the table above? If so, what are they?

Suggest one practical way you or another person could reduce your electricity bills.

Discuss the effect of climate on electricity use. What climate factors might influence which month has the peak electrical use in your area?

Name one other factor (not related to climate) that may influence which month has the highest electricity use.