Circuits That Do Work

By the end of this lesson, you will be able to explain how electrical energy in a complete circuit changes into motion, light, sound, or heat, and name what every working circuit needs.

Think about a flashlight you keep in the closet for a Texas thunderstorm. When the power goes out, you push the switch and the bulb glows. That glow is electrical energy, the energy that moves through wires, changing into light energy. The flashlight did not make new energy. It only changed energy from one form into another.

Energy can change into other forms too. A battery-powered fan turns electrical energy into motion. A doorbell turns it into sound. A hair dryer or a toaster turns it into thermal energy, which is heat energy you can feel. Some devices do more than one job at once. A television gives you both light and sound from the same electrical energy.

None of this works unless the energy has a path to follow. A circuit is a complete loop that electrical energy can travel around. A circuit needs three things. It needs an energy source, like a battery or a wall outlet. It needs wires or other metal parts to carry the energy. It needs a device to use the energy, like a bulb, a motor, or a buzzer. Many circuits also have a switch that opens and closes the loop.

The most important rule is that the loop must be closed. If a wire comes loose, or the switch is open, or a battery is missing, the loop has a gap. Energy stops moving, and the bulb goes dark. That is called an open circuit. Closing the gap makes it a complete circuit again, and the device turns back on.

Try it: If you connect a battery to a small motor with two wires and the motor spins, what form of energy did the electrical energy become?