About this blog

Physics can be difficult to learn, but this blog aims to help you get into physics by connecting your GCSE physics lessons with things you see in the world around you.

Wednesday, 18 May 2011

The Answers Are At Your Fingertips

My friends, the cool people that they are, have been fond of taking the forehead loser ‘L’ to a new level so that they could insult me, and others, further. This insult takes the form of making a 3D 'L', and I can tell you, it’s really very insulting. Once I’d got over the tears and the terror, a thought came to me. That’s just the same as the rule for remembering the intricate details of the motor and dynamo effects! And so my woes were behind me, and the comforting blanket of Physics could be enjoyed once more.

These two opposing rules help you remember the ways that electric currents and magnetic fields interact, a subject close to the heart of all and sundry. Ok, so it doesn’t sound all that exciting, but these effects have plenty of applications across your life, just slightly hidden from view. Electric motors power all sorts of things from hairdryers to power tools to model cars, allowing these things to work with just the push of a button. And the dynamo effect is directly responsible for the nifty way that wind-up torches and light-as-you-cycle bike lights work.

And there are even more exciting reasons why this is important (just when you thought you couldn’t take any more). These show that electricity and magnetism are connected, that when a current flows through a wire, a magnetic current is created. And if you pulsate this current, then a changing field is created, which can be detected. Early discoverers were astonished to find this out, and soon learned to manipulate its effects. This led to the creation of the audio systems we take for granted today, with loudspeakers and the telephone leading the way.

Whilst all this is very interesting though we need to return to the tricky question of why our fingers have the answers. Let’s look at the motor effect first, which is the way a wire with a current flowing through it will move when it’s placed in a magnetic field. This is simple to set up with an electromagnet. Once the electromagnet is switched on, the wire jumps to the side. Which side? Well that’s what Fleming’s left hand rule is for.

On the other hand (groan), if you move a magnet through a coil of wires, then a current will be generated in the wire. This is called the dynamo, or generator, effect and is what Fleming’s right hand rule is for. So, we need to bring the hands into the picture here.

The trick here is to make sure that you know which way the magnetic field runs, which is from North to South, and which way the current goes, from Positive to Negative. Then simply look at the section of the set-up that you need to apply the rule to and there we go! The answers are at your fingertips!

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