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Electricity: Volts and Amps

Date: 10/18/2001 at 14:02:19
From: Chantal Labode
Subject: Electricity

My teacher gave us a project on electricity and one of the questions 
was how electricity is measured. Can you give me a scientific answer?

Date: 10/18/2001 at 15:29:17
From: Doctor Jeremiah
Subject: Re: Electricity

Hi Chantal,

Electricity ismeasured with a measuring device called a voltmeter or 
an ampmeter, because electricity can be measured in two different ways 
and the units of the measurements are volts and amps.

Think of electricity as like water, and a wire as like a hose. How 
would you measure the water coming out of the hose? There are two 
ways: the pressure pushing the water and the amount of water that 
flows through the hose every second.

The pressure pushing the electricity is measured in volts, and the 
amount of electricity that flows through the wire every second is 
measured in amps.

So a car battery is usually around 12 volts of "pressure" and the 
amount of electricity that flows depends on how much is being used at 
the end of the wire. When you start your car the starter uses around 
600 amps. Remember that amps is the amount of electricity per second.
That's why if your car doesn't start pretty quickly, your battery will 
run out of electricity: 600 amps is a lot of electricity per second 
and the battery can only hold so much.

Houses in the U.S. and Canada have electricity that is 120 volts. A 
120-watt lightbulb uses 1 amp. That's because 

   watts = volts x amps

So if you look on the back of an electrical device (or on a lightbulb) 
and it says 1200 watts, and you live in the U.S. or Canada where your 
house has 120 volts, then:

   1200 watts = 120 volts x 10 amps

Houses in other parts of the world have electricity that is 240 volts.  
So if you had a 1200-watt device and you lived in New Zealand (where I 
live) then:

   1200 watts = 240 volts x 5 amps

It would use only 5 amps. The device is only using half as much 
electricity every second.

This is why its important not to play with electricity that comes out 
of the wall. The "pressure" or voltage is 10 times as high as a car 
battery. A little battery like an "AA" or "C" size battery is only 
1.5 volts, so the wall electricity is almost 100 times that 
"pressure," and that can cause big problems for things that are not
designed to handle that kind of pressure. People, for example, are not 
designed to handle that much voltage and that is why people get really 
hurt when they mess around with electricity.

Write back if you want to know more.

- Doctor Jeremiah, The Math Forum   
Associated Topics:
High School Physics/Chemistry

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