Resisitivty PAG

Question 1

Equipment

Answer 1

● 1m long constantan (copper–nickel alloy) wire
● Voltmeter
● Ammeter
● Low voltage power supply
● Micrometer
● Metre ruler

Question 2

Method

Answer 2

1. Measure the diameter of the constantan
   wire at 3 points along its length using the
   micrometer, and calculate the mean
   diameter.
   . Adjust length l to 10 cm using the crocodile
   clips and metre ruler.
2. Read and record the current (I) on the
   ammeter and the voltage (V) on the voltmeter. Calculate the resistance (R) by using
   R=V/I and record this value.
3. Switch the circuit off in between readings to prevent heating of components which
   could affect their resistance.
4. Increase l by 10 cm and repeat the above two steps, increasing l by 10 cm each time
   up to 80 cm.
5. Repeat the experiment twice more, then calculate the mean resistance for each
   length.

Question 3

Calculations

Answer 3

● Calculate cross sectional area of the wire

● Plot a graph of the mean resistance against length and draw a line of best fit, the
resistivity will be the gradient multiplied by the cross-sectional area of the wire.
ρ = then divide through by A to find . l

R/L is the gradient of the graph hence resistivity is found by the gradient multiplied by
the cross sectional area.