Now we look at the voltage across resistors when we have two or more wired together in series.
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.
In electronic circuits we often find that we need a voltage less than the supply (power source). So, what do we do when this happens? Well, we use two resistors to divide the voltage. Connect a lead into the yellow and black sockets. Now move the rotary switch to position A. Before we fire up the circuit let’s have a look at what we have got. The current will flow from the rotary switch through two resistors and back to the battery. Both resistors have the same value of 1k (1000) ohms. Whatever the current flowing, half the supply voltage we be across each of the two resistors.
Now press and hold either of the red buttons down and look at the readings on the two meters. They should be reading the same value confirming the voltage has been split equally. Now take the lead out of the black socket and put it into either of the red ones and move the rotary switch to position B. This time the meter readings are different because we have an un-even split of 1/3rd and 2/3rds. Now move the lead into the other red socket and you will see the meter readings reverse.
This all means that we can use different value resistors to get any voltage we need. Now move the rotary switch to position C. In this part of the circuit one of the resistors is light sensitive meaning that the resistance will change with brightness. Plug the lead into the yellow and green sockets and mpress a red button down. Put your finger over the light dependant resistor (LDR) and you will see the voltages change. Now shine a light onto it and you will see then change again.
By moving the rotary switch to position D and plugging the cable in the yellow and blue sockets we can see how the variable resistor works. By turning the black knob, we can change the meters from zero to the full supply voltage.
We do need to be careful with this technique and it only really works when we are using small currents. In this example each meter also acts as a 5k resistor and this will affect the voltages. As we are using 1k resistors here it will not be very significant but it is something that can be a considerable.