Paper 3: Required practical 5 - Determination of resistivity of a wire

Question 1

How can the length of the conducting wire be varied when carrying out this experiment?

Answer 1

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

Question 2

Why should the power supply be switched off during readings?

Answer 2

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

Question 3

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

Answer 3

• Temperature changes can affect the resistance of the wire
• Temperature is the control variable

Question 4

How can the resistivity of a wire be determined from a graph of resistance against length?

Answer 4

Gradient of the graph will be R/L and so by multiplying the gradient by the wire’s cross-sectional area, you will obtain the wire’s resisitivity

Question 5

Why should the current, used in this experiment, be kept low?

Answer 5

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