Now we move to capacitors and we look at one of the main uses for this important components.
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.
Capacitors can be used for a number of things, but the one we will look at here is when we use them as a sort of small rechargeable battery. But before we use them let's look at the rest of the circuit but moving the rotary switches to positions A and E. Then press and hold the red button down and then press and release the yellow button. Yon will see that when the yellow button is down the LED light comes on.
Remember how the transistor works? Well, when we give a voltage to the B (base) connector that it turns the transistor on and allows current to flow from the C (collector) to E (emitter). As soon as we lift the yellow button then we have no voltage so the transistor is turned off and the light goes out.
Now move the first rotary switch to position B and try the yellow button again. Note that when it is released the light stays on for a short time. So, what’s happening? Well, the first capacitor is now part of the circuit and is being charged up when the yellow button connects it. Think of this as charging a rechargeable battery that only takes a very short time to fully charge. When the yellow button is lifted this capacitor provides the voltage to keep the transistor switched on. It doesn’t last very long because very soon the capacitor goes flat. But we can do something about this! It is discharging through the first resistor, but moving the rotary switch to use a resistor of a higher value will reduce the current and slow down the discharge.
Try all 9 options you get with the rotary switches in their first three positions and record the time the LED light is on. Use these values to try and work out how long the light will stay on when both switches are in their 4th position.