Resisting the Flow

You will remember that in the bow and arrow drawing from our

Junior Electronics Fact Sheet No 1

...we learned the difference in electricity between a) voltage - expressed inVOLTS and b) current which we express in AMPERES, or simply Amps. Furthermore, for this exercise keep in mind that we can pull the string tension from just a little to (if the bow is strong enough) quite a lot. Also, the tension can remain as long as the arrow is not released and nothing is happening.

What this leads up to is the following: We cannot see electricity. We can only feel it, hear it or see WHAT IS DOES. And while we find it difficult to imagine how electricity really behaves, we get some idea when we use 'helpers' such as the bow and arrow, or water and maybe others. Here is another example.

Let us imagine that the tanks are full of water and really big. The outlet pipe at the tank on the left is as thin as a drinking straw. The pipe on the right, however, is wide enough for you to walk through. On the left, can you imagine how great the RESISTANCE is to the flow of water? We would have to increase the tension a lot to get a large quantity of water delivered. On the right, by contrast, there is almost no resistance. In seconds we'd get totally flooded.

Now go back to electricity. Here again, the similarities are quite easily to grasp. In any electric circuit, unless there is resistance to the current flow, our batteries would be empty in a short time, or, in our domestic power supply we'd get what we call a SHORT CIRCUIT.

With resistance and current, it is a bit like a seesaw - as one goes up, the other goes down. If the resistance is high, little current will flow. As the resistance gets less, more current will flow. If there is a short circuit in our house power supply, (maybe caused by a faulty appliance) to avoid setting fire to our house, it must be protected by fuses or circuit breakers. These will cut off the electron flow as soon as it becomes dangerously high.

In our next fact sheet we will talk about resistors and then how we can work with all three values:
a) Voltage, b) Current and c) Resistance. Next Fact Sheet No 3.

Click here to return to Fact Sheet links

If you have any questions you may send them to my mail address.

Disclaimer

Copyright © 1997-2010 Peter Schmedding, Child Development Projects, Canberra, Australia.