Determination of Resistivity of a Wire

Question 1

How does the resistance of a wire change when the cross sectional area decreases

Answer 1

The resistance of a wire is inversley proportioanl to the cross sectional and so as the area decreases the resistance will increase

Question 2

How does the resistance of wire change when the length is decreased

Answer 2

The resistance of a wire directly proportional to the length of the wire so as the length of the wire decreases its resistance also decreases

Question 3

What is the Unit of Resistivity

Answer 3

Ωm

Question 4

How do you ascertain the cross sectional area of a thin wire

Answer 4

• Using a micrometer measure the wire’s diameter in at least three different places along the wire
• Then input the average diameter into the circular area equation

Question 5

Suggest how the length of conducting wire can be varied when carrying out this experiment

Answer 5

• One end of the wire can be fixed and the other end can be connected to the circuit using a crocodile clip
• The length of conducting wire can be changed by varying the position of the crocodile clip

Question 6

Why should the power supply be switched off between readings

Answer 6

• The temperature of the wire should remain constant throughout the experiment
• Switching the power supply off between readings will help ensure this to reduce the effect of heating the wire

Question 7

Why should the temperature of the wire remain constant throughout this experiment

Answer 7

Temperature changes can affect the resistance of the wire

Question 8

Why does the resiatance of a wire increase when its temperature increases

Answer 8

• As temperature increases the metal ions gain more kinetic energy and so vibrate more
• These vibrating ions make it harder for charge to pass through the wire and so the wire’s resistance increases

Question 9

How can the resistivty of a wire be determined from a graph of resiatance against length

Answer 9

The gradient of the graph will be R/L so the gradient mutlipled by the cross sectional area will give the resistivity

Question 10

Why should the current used in this experiment be kept low

Answer 10

• As current increases the temperature of the wire will increases
• By keeping the current low the heating effect is kept to a minimum