RP2: Resistance of a Wire

Question 1

Method (5p)

Answer 1

1) Set up equipment as shown and connect the first length of wire to crocodile clips
2) Turn on battery and measure the voltage on a voltmeter and current on an ammeter
3) Work out resistance using R= V/I
4 Repeat to get a mean
5) Repeat using different lengths of wire

Question 2

Independent variable

Answer 2

Length of wire

Question 3

Dependant variable

Answer 3

The resistance

Question 4

Control variables

Answer 4

• Measure length of wire with a ruler
• Repeat to get a mean
• Switch off between readings to avoid heating the wire

Question 5

Why must the battery be switched off between readings? (3p)

Answer 5

• Causes the wire to heat up
• Heating of the wire increases resistance and reduces current
• This changes the results

Question 6

Reason for relationship between resistance and length: (As the wire length increases, so does the resistance) (3p)

Answer 6

• As electrons move down the wire, they collide with ions
• As the length increases, there are more collisions with electeols
• Therefore resistance increases as length of wire increases

Question 7

Why does resistance increase when wire heats up? (2p)

Answer 7

• When wire heats up, electrons vibrate more
• This increases the resistance as electrons collide with ions more

Question 8

Why is a variable resistor used?

Answer 8

To keep the circuit resistance and the current the same

Question 9

Risk assessment for any hazards (3p)

Answer 9

• Current in wire is too hight
• So the wore could burn you
• Having a switch would prevent this