Edexcel - London Examinations GCE, May 1997 - Paper 2 Question 2

1. a) i)

a) ii) Method:

1. Connect one of the resistors, after measuring the length of resistance wire used as shown in the diagram above.

 2. Switch on the supply and note the ammeter and voltmeter readings. Connect an equal length of resistance wire in series with the first one. This will double the length of wire used.

 3. Note the new meter readings.

 4. Repeat the experiment each time connecting an identical resistor in series with the rest.

 5. Each time measure the new reading of the ammeter (current) and voltmeter (voltage).

 6. Calculate the resistance from R = V / I or voltmeter reading divided by ammeter reading.

  You can tabulate your results as follows:

  

Voltmeter reading, V (in volts)
Ammeter reading, I (in amperes)
R = V / I (in ohms)
Length of wire, l, in cms

 iv) If a graph of R is then plotted against length (l) a straight line through the origin is then obtained. So one can conclude that the resistance is directly proportional to the length or R µ l. (12 marks)

 b) See graph below:

The resistors are connected in parallel as the total resistance decreases with the number of resistors.

From the graph, one can see that the resistance decreases as the cross-sectional area increases

In fact R is inversely proportional to A (cross-sectional area) (8 marks)