Thinking about loops

Electrical loops connect

A battery is running down because it's linked to a glowing bulb which can be a long way off. This link is always a loop, which suggests something going around, allowing this long-distance connection between the running down and the glowing. Something seems to travel inside the wires where you cannot see it.

Use a rope loop to make a useful picture to think about the electrical loop. You can see (and feel) what is happening in the rope loop. And the rope loop can be as long as you choose, just like the electric loop.

Try out a rope loop

Start with a single loop of rope. For the bulb, get a friend to grab the rope loosely. Change how tightly they grab the rope to change the bulb.

For the battery you grip the rope, and pull, hand over hand.

The rope will move everywhere at once. If you've chosen well, as you keep pulling, your friend's hand will be warming. You – the battery – are running down, the bulb is glowing.

The harder you pull the rope, the faster the rope moves, and there is more warming in the bulb .

Just like an electrical loop, what you do over here, wearing out the "battery", makes the bulb warm over there.

So long as there is some running-down over here, and a complete loop, there can be some useful-doing over there (you probably know there are electric heaters and motors so that you can do more than lighting).

Change the bulb by grabbing the rope more tightly. Tighter grabbing slows down the rope, resisting the rope sliding through your friend's hand.

Compare the loops

Both loops behave in the same way. Changes you make in one show you what to expect in the other.