Required practical 3 investigates what affects resistance. To test the length of a wire at constant temperature, connect an ammeter in series with the wire and a voltmeter in parallel with it. Measure the current and potential difference for different lengths, then calculate R = V / I.
A longer wire has a greater resistance.
Keep the current small so the wire does not heat up, because temperature would change the result. The same circuit is used to test combinations of resistors.
In series, the total resistance is the sum of the resistances, so it is greater than any one resistor.In parallel, the total resistance is smaller than the smallest resistor.
In required practical 4, to measure the resistance of a component, connect an ammeter in series with it and a voltmeter in parallel across it. Read the current and the potential difference, then divide potential difference by current.Then plot a graph of current against potential difference for a resistor at constant temperature, a filament lamp and a diode.