Here we refresh our understanding of electromagnetic induction in preparation of the next board.
Youtube video, suitable whether of not you have the board with you.
See board images.
Tutorial guide for when you have the board with you.
Just for a moment we are going back to looking at electromagnets. This is really in preparation for the next board.
Here we have a ferrite (iron) rod with three coils of thin copper wire wrapped round it. You can see this on the right side of the board. How these are wired to the other bits on the board can bee seen by the diagram in the middle. One coil is connected to the battery and switch, one to the two LEDs which point in different directions and the third coil connects to the centre-point ammeter.
Ensure the toggle switch is in the up position and then press the red button down for no longer than 3 seconds and then let it go. As you do this, watch the LED lights. As you press the red button one of the lights flashes on and when you release the button the other one does the same.
So, what’s happening. Well, when we pressed the button, it started a current flowing through the first coil. As this happens, we can think of the magnetic field springing out of the coil and the iron rod inside it. It’s this change in the field that creates a current in the other two coils and only happens when we press the button and then when we release it. It doesn’t happen when the button is held down. So it’s not the current flowing, but the change in current.
When the field springs out, the current in the 2nd and 3rd coil flows one way and then when the field collapses the current flows the other way. This is why one LED lights up when we press the red button and then the other one lights up when we release the button.
The ammeter at the top of the board will show a very small deflection when we press and release the red button. It is very little because the current we generate is very small and only lasts a fraction of a second. But you will see if deflect one way when the button is pressed and then the other way when its released.
If we throw the Reverse Polarity switch, it means that the current flows through the first coil the other way round. Now the LEDs will light up the other way round as well and the ammeter deflection will also be reversed.There are two reasons why we should only hold down the button for a short time. Firstly, the coil draws a lot of current from the battery and these will get flat very quickly if the circuit is on for too long. But more importantly, the current is so high that it will make the coil hot there is a real risk of the wire melting and breaking it. Please don’t try this!!!!!