Energy
Circuits and their components
Name the parts of a torch circuit and what each does, read a circuit diagram's symbols, tell a conductor from an insulator, and say when a lamp glows and when it does not.
A torch is the whole of this chapter in your hand. Slide the switch one way and the lamp lights; slide it back and it goes dark. Nothing has been added or taken away — the same cells, the same lamp, the same wires. What changed is whether the path from one terminal of the cell round to the other is joined up or broken.
The four parts of a torch circuit
An electric cell is a portable source of electrical energy, with a metal cap for its positive terminal and a flat metal disc for its negative one. Join two or more cells cap-to-disc and you have a battery. The lamp turns the energy into light. The switch joins the path up or breaks it. Wires carry the current between them.
Safety, as the chapter states it
The experiments here use cells — the kind in a torch, a wall clock or a remote. Mains sockets and portable generators are a different matter: they can injure or kill, so leave those to an adult and treat a danger sign on a pole or an appliance as the warning it is.
Have a play
Take apart an incandescent torch lamp and look at what makes the light.
Tap any part of the picture.
Worked example
An LED is wired to a two-cell battery and stays dark. The wires are swapped over and it lights. Why?
Look at the LED's two wires: one is longer than the other. The longer one is its positive terminal.
An LED is not symmetrical the way an incandescent lamp is. Its two ends are different, and the lengths are how you tell which is which.
Try it together
A torch circuit is built and the lamp stays dark. Work through what a dark lamp can be telling you.
The first two steps take yes or no; the last one wants a word.
1.The switch is in its OFF position. Is there a complete path for current round this circuit?
Have a go
Have a go on your own. Electricity that comes from a cell or a battery is one of two kinds, and the other is what arrives at a wall socket. Which kind does a battery give? Give the two words.
Ready to practice?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.