Download Name: Block: ______ Science 9 – Ch. 11 Using Electricity 11.2

Name: ___________________________
Block: __________
Science 9 – Ch. 11 Using Electricity
11.2 Electrical Energy and Power
A. Electrical Energy, Time & Power
Electrical power - ____________________________________________________________
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The following formula can be used to calculate the electrical power of a device:
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Although it is difficult to measure power, we can calculate by using
and the following formula:
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The 2 above formulas enable us to create a third formula:
Sample Problems:
1.
A laser pointer used 0.045J of electrical energy during 15s of operation. What is the
power of the laser pointer?
2.
A 100W light bulb is left on for 3 h. How much electrical energy did it use? Express
your answer in scientific notation.
3.
A laptop computer operates on 14W of power. If the battery has 200 kJ of electrical
energy stored, how many hours can you use the computer before you need to recharge
the battery?
4.
A light bulb has a current of 0.625A when it is plugged into a 120V outlet. What is the
power of the light bulb?
5.
The power of the resistor shown below is 0.5W. If the current is 0.382A, what is the
voltage of the resistor?
6.
An electronic gaming system is rated at 380W. When a student plugs the system into a
120V outlet, what is the current in the system?
7.
A resistor has a current of 0.28A and a voltage of 4.5V. If the current flows for 50s,
how much electrical energy is transformed into heat?
Practice Problems:
1.
What is the power of a toaster that converts 24 000 J of electrical energy into thermal
energy in 35s?
2.
A car headlight has a power rating of 45W. How much electrical energy does it require
in 28 min.?
3.
A car battery can produce 4000W of electrical power to start a car. If the car uses
3000J of electrical energy to start, how long does it take to start the car?
4.
A solar cell produces 1.8A of current at 0.42V. What is the power of the solar cell?
5.
A 37W cordless drill uses a current of 2.6A. What is the voltage of the battery?
6.
What is the current I a 95W TV set that is connected to a 120V household outlet?
7.
A light bulb has a current of 0.5A when it is connected to a 120V household outlet. If
the light is left on for 30 min., how much electrical energy is used by the light bulb?
11.2 assignment CYU’s #1-11