Power means strength, or force or energy. To a scientist, power is the rate at which work is done or energy is used. Electric power is a measure of the rate at which electricity does work or provides energy.

For example, the power used to run a dishwasher is 2300 watts.

Watts (W) are the units in which electric power is measured.

Now remember, electric power measures the rate at which electricity does work or provides energy.

Electric power can be calculated by using the following equation:
Power = Voltage x Current or P = V x 1

Another way to put it is Watts = Volts x Amperes

THE GALVANOMETER

PROBLEM: Can we build a simple, accurate device to measure the rate of flow of electrons through a circuit?

MATERIALS:

• A metre stick
• tape
• Tin foil
• straight plastic straws
• 30 or 32 gauge thin insulated wire (at least 3 metres) Speaker wire is very common and works well
• Wire cutters
• a small glass jar
• a knife or scissors
• bare copper wire
• a small but powerful magnet
• a variety of dry cells (batteries)

PROCEDURE:

(image 1)	(image 2)	(image 3)	(image 4)	(image 5)

1. Assemble all of the required materials.Wrap three meters of wire around the neck of the jar. Allow for 15 centimetres of extra wire at each end. (see image 1)
2. Twist the two ends together. (see image 1)
3. Strip about 2 centimetres of insulation off of the ends of the two wires. (see image 1)
4. Using tin foil, make two 1 cm square contact pads and attach them to the wires. (see image 2)
5. Cut a second piece of wire so that it will hang across the opening of the jar.
6. Strip that piece of wire of its insulation, and straighten this wire as much as possible.
7. Tape the magnet to the wire. (see image 3)
8. Cut two notches in the end of the straw. (see image 3)
9. Tape this straw to the magnet and the wire. (see image 4)
10. Rest the wire arms on the mouth of the jar. The straw should be pointing straight up. If it isn't, make sure the stripped wire arms are straight. If they bend under the weight of the magnet, you might need to use heavier gauge wire for the arms. If the straw still refuses to stand freely upright, try extending the slots farther up the straw so that the straw slide down farther over the magnet. (see image 5)
11. This completes the construction of the "Galvanometer".

OBSERVATION:

Test the galvanometer by touching each of the arms to a dry cell.

1. What happens?
2. What happens if you turn the battery around? Why?
3. What happens if you use a more or less powerful battery? Explain.
4. Using different batteries, can you create a scale which you could use to measure the voltage of some unknown batteries?
5. What do you suppose is happening in this experiment? Create and explain your hypothesis.

EXTENSION

The more wire that you wrap around the jar, the more sensitive the galvanometer. Why? Try building a new galvanometer using 12 metres of wire instead of 3!

DID YOU KNOW?

The galvanometer gets its name from an italian scientist, Luigi Galvani. Galvani made the first recorded discovery of electric current. He attached a brass hook to the spinal cord of a dead frog laid on an iron plate. When he pressed the other end of the hook to the iron plate, the frog's legs "jumped."