Required practical 3 - investigating factors affecting resistance

Question 1

what is the aim of this investigation? (part 1 - resistance wire)

Answer 1

to investigate how changing the length of wire affects it’s resistance

Question 2

how would you conducts this experiment? (part 1 - resistance wire)

Answer 2

1. set up a circuit containing an ammeter, a voltmeter, a power supply, a switch, resistance wire, crocodile clips and a metre ruler
2. put one crocodile clip at the 0cm position and keep it fixed there
3. put another crocodile clip at 10cm - this one can move along the wire and adjust the length of wire being used
4. record the readings on the ammeter and voltmeter
5. move one crocodile clip 10cm further
6. record the new reading on the ammeter and voltmeter
7. repeat this process by moving the crocodile clip 10cm further each time until you reach the end of the wire
8. use the results to calculate the resistance of each length of wire using V = IR
9. plot a graph of resistance against length for the resistance wire

Question 3

what kind of graph should you get from your results? (part 1 - resistance wire)

Answer 3

• length should be on the x-axis
• resistance should be on the y-axis
• you should have a straight line that passes through the origin

Question 4

what conclusions can you draw from the results? (part 1 - resistance wire)

Answer 4

the longer the piece of wire, the higher the resistance and the line goes through the origin - resistance is directly proportional to length

Question 5

what are some hazards associated with this practical and how are they managed? (part 1 - resistance wire)

Answer 5

• heating the resistance wire - burns to the skin - don’t touch the resistance wire while the circuit is connected + allow wire time to cool

Question 6

how may the results not be as accurate as they could be? (part 1 - resistance wire)

Answer 6

• the first crocodile clip might not be exactly on 0cm so the graph might not go through the origin
• measurements might be slightly longer or shorter than the true values - systematic error from not putting it on 0cm
• contact resistance in every circuit between components - systematic error

Question 7

what is the aim of the experiment? (part 2 - resistors)

Answer 7

compare the total resistance in series and parallel arrangements of resistors

Question 8

how do you conduct the experiment for resistors in series? (part 2 - resistors)

Answer 8

1. construct a circuit containing a resistor, a power supply and an ammeter
2. measure the current through the circuit using the ammeter
3. use this value and the pd of the power supply to calculate resistance using V = IR
4. add another resistor in series
5. again measure the current and use the pd of the power supply to work out the resistance
6. repeat steps 4 and 5 until you have done it with 4 resistors in series

Question 9

how would you conduct this experiment for resistors in parallel? (part 2 - resistors)

Answer 9

1. set up a circuit containing a resistor, a power supply and an ammeter
2. measure current through the circuit using the ammeter
3. use this value and the pd of the power supply to calculate resistance using V = IR
4. add another resistor but in parallel this time instead of in series
5. measure current and use the pd of the battery to work out resistance using V = IR
6. repeat steps 4 and 5 until you have added all 4 resistors in parallel

Question 10

what conclusions can you draw from the experiments with resistors connected in series and parallel? (part 2 - resistors)

Answer 10

• in series, the resistance of the network is equal to the sum of the individual resistances - there is only one path for the electrons to take, through both resistors
• in parallel, the resistance of the network is less than any of the individual resistances because total current through the circuit increases so total resistance of the circuit decreases

Question 11

what sort of graph do you get for connecting resistors in series? (part 2 - resistors)

Answer 11

• resistance is on the y-axis
• number of identical resistors is on the x-axis
• the line of best fit is a straight line

Question 12

what kind of graph do you get for connecting resistors in parallel? (part 2 - resistors)

Answer 12

• resistance is on the y-axis
• number of identical resistors is on the x-axis
• the line of best fit curves downwards - it is an inversely proportional graph

Question 13

what are the hazards associated with this practical and how were they managed?

Answer 13

• heating of wires - minor burns - set up the circuit before closing the switch