4. 2 THE ELECTRIC CIRCUIT
Can you make a torch bulb light? Some bulbs need two batteries to light them properly, so you can use two batteries as well as the bulb. You are also allowed two pieces of wire. Try it yourself if possible.
The illustration below shows a good answer. Before you continue, study it closely, and check that it works.
The bulb. Notice that one wire must touch the metal point at the bottom of the bulb. The other wire must touch the metal side below the glass bulb. You will learn more about bulbs in Section 4.5.
The batteries. Notice that the two batteries must point the same way. The top of one battery must touch the bottom of the other. One wire must touch the top of the two batteries, and the other wire must touch the bottom. You will learn more about batteries in Section 4.6.
The wires. One wire carries the electricity from the top of one battery to the bulb. The other wire carries the electricity back from the bulb to the bottom of the other battery. That second wire is a surprise to some people! The electricity will only flow, and light the bulb, if it can get back to the battery again. We say that electricity only flows when there is a complete, unbroken circuit. The circuit is the path that the electricity flows along. A circuit always starts from one end of a battery and returns to the opposite end. The electricity flowing around a circuit is called an electric current. If there is any break in the circuit, the electric current will not flow and the bulb will not light. Try it and see!
- 1. Where must the two wires touch the bulb? Does it matter which wire touches which place? (If you are not sure, try it!)
- 2. (i) How must the batteries be placed, and (ii) where must the wires touch the batteries?
- 3. What is an electric circuit? What kind of circuit is needed before an electric current can flow?
- 4. The illustrations opposite show how some students joined up their batteries and wires and bulbs.
(i) Which of the bulbs will light?
(ii) Why will each of the other bulbs not light?
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