Core Practical 2: Resistivity of a material

Question 1

CP2 Equipment List

Answer 1

Ammeter
- Determine current through wire
Voltmeter
- Determine voltage across wire
2m of wire
Crocodile clips
- Allow connection to wire
Metre ruler*
- Measure length of wire
Micrometer
- Measure diameter of wire
Power supply
- Provide voltage across wire

Question 2

CP2 Method

Answer 2

1. 5-10 measurements of diameter
2. Connect ammeter in series, voltmeter in parallel
3. Touch one end of clip at 10cm intervals
4. Record voltage and current
5. Calculate resistance for each interval
6. Plot graph R against L
7. Gradient = ρ/A

Question 3

Safety measures CP2

Answer 3

Small voltage
- Little danger of shock
Don’t touch wire
- Wire may get warm

Question 4

CP2 Eval

Answer 4

Ohm-meter
Uncertainty of diameter increased
- Radius has to squared, u doubles
Faulty crocodile clips
- Resistance values inaccurate
Current causes heating effect
- Changes resistance; inaccurate value of ρ
Deformation of wire
- Pressure on wire will cause deformation
Straight wire
- Length measurement accurate

Question 5

Potential systematic errors

Answer 5

Non-zero resistance
- shifts graph up; gradient same