For an electrical circuit to do something, current must flow. We imagine an "electrical fluid" that emerges from the positive end of the battery. The electrical fluid is called charge; what is actually moving are electrons (it is a small complication that we will ignore hereafter that the electrons actually are going the opposite direction from the current itself. There is no experiment we can do here that can reveal which way things are going.) Electrical current is measured in a unit called the ampere. This is the electrical analog of the flow rate of a liquid -- like gallons per minute. The light bulb in your kit, connected to two batteries (as in a flashlight) has a current of 0.33 Amperes. A car battery produces a current of several hundred amperes while starting the engine.

Electrical current is necessary to deliver electrical energy, but current and energy are not the same thing. If it was energy that was coming down the wires, you would only need one wire to light a light bulb. (We will discuss current and power more in the next section).
Electrical devices

We have met several electrical devices in this section.

Wires and switches The current has to stay inside a conductor. So we can guide the current to the place we want, using wires.

A battery is a way to turn chemical energy into electrical energy. We will study them in the next section. Their equivalent in the siphon system was the difference in height between the two water levels being connected.

A light bulb is a very fine wire made of tungsten, sealed in an inert gas atmosphere. When a current is flowing through the wire, electrical energy is converted to heat, which makes the wire extremely hot -- almost 1000oF! Objects this hot give off visible light, and there is your light bulb. The fine wire is in the form of a coil, and the symbol for a light bulb is a picture of this, too. The two ends of the fine wire are connected to the two electrical contacts on the base of the light bulb, so that we can cause a current to flow through it. A light bulb turns electrical energy into heat no matter which way the current flows.

A motor lets us turn electrical energy into mechanical energy. Inside the motor you would find magnets and electromagnets, which we will study later.

Current in Circuits

We cannot see electrical current, and so it is not entirely clear what is happening when we make a circuit. The activities in this section have tried to make the flowing current real.

In the first set of activities ( Electrical currents and simple circuits), we found that we must make a circuit before anything can happen. The current must stay in the wires, and has to go somewhere; we can only have current through a device if the current can circulate through it and through the battery (which provides energy).

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