Practical - factors that affect resistance - Circuits - AQA Synergy - GCSE Combined Science Revision - AQA Synergy

Required practical - factors that affect resistance

There are different ways to investigate the factors that affect . In this required practical activity, it is important to:

record the length of the wire accurately
measure and observe the and
use appropriate apparatus and methods to measure current and potential difference to work out the resistance

Circuit with a 1.5 V cell, ammeter, voltmeter and thin resistance wire connected in parallel. Length of wire is measured using a meter ruler.

Aim:

To investigate how changing the length of the wire affects its resistance.

Method:

Connect the circuit as shown in the diagram above.
Connect the crocodile clips to the resistance wire, 100 centimetres (cm) apart.
Record the reading on the and on the .
Move one of the crocodile clips closer until they are 90 cm apart.
Record the new readings on the ammeter and the voltmeter.
Repeat the previous steps reducing the length of the wire by 10 cm each time down to a minimum length of 10 cm.
Use the results to calculate the resistance of each length of wire by using \(\text{R} = \frac{\text{V}}{\text{I}}\), where \(\text{R}\) is resistance, \(\text{V}\) is and \(\text{I}\) is current.
Plot a graph of resistance against length for the resistance wire.

Results:

Some example results may be:

Length (cm)	Potential difference (V)	Current (A)	Resistance (Ω)
100	1.20	0.16	7.5
90	1.18	0.17	6.8
80	1.00	0.17	5.9
70	0.96	0.18	5.3
60	0.93	0.21	4.4
50	0.89	0.25	3.6
40	0.84	0.27	3.1
30	0.75	0.31	2.4
20	0.63	0.44	1.4
10	0.41	0.63	0.7

Length (cm)	100
Potential difference (V)	1.20
Current (A)	0.16
Resistance (Ω)	7.5

Length (cm)	90
Potential difference (V)	1.18
Current (A)	0.17
Resistance (Ω)	6.8

Length (cm)	80
Potential difference (V)	1.00
Current (A)	0.17
Resistance (Ω)	5.9

Length (cm)	70
Potential difference (V)	0.96
Current (A)	0.18
Resistance (Ω)	5.3

Length (cm)	60
Potential difference (V)	0.93
Current (A)	0.21
Resistance (Ω)	4.4

Length (cm)	50
Potential difference (V)	0.89
Current (A)	0.25
Resistance (Ω)	3.6

Length (cm)	40
Potential difference (V)	0.84
Current (A)	0.27
Resistance (Ω)	3.1

Length (cm)	30
Potential difference (V)	0.75
Current (A)	0.31
Resistance (Ω)	2.4

Length (cm)	20
Potential difference (V)	0.63
Current (A)	0.44
Resistance (Ω)	1.4

Length (cm)	10
Potential difference (V)	0.41
Current (A)	0.63
Resistance (Ω)	0.7

Analysis:

Graph plotting length against resistance, line of best fit shows a direct positive correlation.

Evaluation:

From the graph it can be seen that the longer the piece of wire, the higher the resistance, and that resistance is directly proportional to length as the graph gives a straight line through the origin.

Hazards and control measures

Hazard	Consequence	Control Measures
Heating of the resistance wire	Burns to the skin	Do not touch the resistance wire whilst the circuit is connected and allow time for the wire to cool.

Hazard	Heating of the resistance wire
Consequence	Burns to the skin
Control Measures	Do not touch the resistance wire whilst the circuit is connected and allow time for the wire to cool.

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