ELECTRICAL ENERGY: Electricity Circuits

Unlike water in a pipe or peas in a straw, electric current must flow in a circuit. The electrons leave from a source, travel through wires and come back to the same source. Some possible sources of electricity are:

• Batteries (also called voltaic cells)
• Photovoltaic cells (also called solar cells)
• Power plants

All three create a voltage that pushes electrons around a closed path. If the path or circuit is broken, the current will not flow. This is how a switch works.

In this flashlight circuit, electrons leave from the negative end of the battery, flow through the light bulb, and reenter the battery at the positive end. The amount of current that leaves the battery is exactly the same as the amount that comes back in. Along the way, the current delivers electrical energy to the light bulb.

Any time a voltage pushes a current through a circuit, electrical energy is produced. The flow of electrical energy in a circuit is called the power. It is measured in watts, and can be calculated like this:

volts x amperes = watts

A simple flashlight circuit has a 6-volt battery, pushing 2 amps of current through. How many watts does it produce?

Twelve watts of power is enough to make a flashlight bulb glow brightly, but it won't do much at all for a regular light bulb, which consumes 40 to 100 watts of power, or for the average computer (200 watts), toaster (900 watts), or microwave oven (1200 watts). That's why most homes, schools, and businesses rely on the higher voltage electrical energy that is made and delivered by a power plant.

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