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# Electric Power and Electrical Energy Use

## The rate at which a device changes electric current to another form of energy and it's SI Unit of measurement.

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### Transforming Your Life

Credit: Charger image: Mmckinley Transformer Image: Bill Bradford
Source: http://commons.wikimedia.org/wiki/File:Chargepod_2.jpg http://www.flickr.com/photos/mrbill/2547622226
License: CC BY-NC 3.0

You probably recognize the objects in both of these photos. On the left is an electronics charger (this particular one, for multiple devices). On the right is an electric transformer mounted on a power pole. There is likely to be one of these not far from your home. Both objects transform electricity.

#### Why It Matters

• You can’t plug your cell phone directly into an electric outlet in your house. It has too much voltage. The electricity would “fry” the phone.
• The same goes for the electric poles outside your house. They carry high-voltage electricity that would blow out all the circuits in your house.
• That’s where electric transformers come in. They reduce the voltage of electric current and make it safe for home circuits and electric devices. Without transformers, much of modern life would be impossible.
• Credit: Victoria Catterson
Source: http://www.flickr.com/photos/cowlet/36528536/
License: CC BY-NC 3.0

A transformer's size depends on the amount of voltage it needs to handle [Figure2]

• Watch this video to see how a transformer works:

#### Show What You Know

1. What is voltage?
2. The voltage of electricity traveling away from a power plant is very high. How high may it be? Why is the voltage so high?
3. What type of transformer lowers the voltage from one current to another? Describe this type of transformer, and explain how it works.
4. How high is the voltage of electricity that enters your house or apartment building? What type of transformer changes the voltage in a power line to voltage that is safe for a home? Where is it located?
5. Additional transformers are needed to step-down voltage in home circuits. That’s because the voltage required by home appliances and electric devices varies. Give some examples.
6. If you plug a cell phone charger into a wall outlet, how many volts of electricity go into the charger from the outlet? How many volts of electricity go from the charger into your phone? What type of transformer is a cell phone charger?

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