CP2 Finding the Resistivity of a wire

Question 1

How do you find the cross-sectional area of the wire?

Answer 1

area of a circle is pi(r^2)
use a micrometer at 6 or more points on the wire and make an average ignoring any anomalies

Question 2

How?

Answer 2

Series circuit with a power supply variable resistor, ammeter and the wire.
voltmeter in parallel with them all

Question 3

How?

Answer 3

Vary the length of the wire at 10cm intervals using crocodile clips (one being fixed on one end of the wire) record the current and voltage and use these values to find R

Question 4

Graph?

Answer 4

R on the y-axis and L of x-axis
Resistivity will be the gradient x Area

Question 5

Reducing uncertainty?

Answer 5

Keep the temperature constant so:
low current
turn off the power supply between readings
clean croc clips
Make sure the wire is straight
use an ohm-meter instead of varying V and I

Question 6

Why does the temperature need to remain constant?

Answer 6

As temperature increases the ions vibrate more making it harder for current to pass through so resistance increases

Question 7

Why can you use a wire for measuring the resistivity of a metal?

Answer 7

Its resistance is measurable and not as small as a wire

Question 8

What shape of plastic should you use to measure its resistivity?

Answer 8

A thick and short sample, so that its resistance is measurable.

Question 9

What might increase the uncertainty of the test?

Answer 9

Resistance between the clip and the wire
Clip not being at zero
Contact resistance.