Materials

Q3. This question is about the determination of the Young modulus of the metal of a wire.

In an experiment, two vertical wires P and Q are suspended from a fixed support.

The fixed part of a vernier scale is attached to P and the moving part of the scale is attached to Q.

The divisions on the fixed part of the scale are in mm.

An empty mass hanger is attached to Q and the scale is set to zero.

A load is added to the mass hanger so that the extension of Q can be measured as shown in the diagram below.

(a) The reading on the vernier scale can be used to determine ∆l, the extension of Q. Determine ∆l using the diagram.

[1 mark]

(b) The graph below shows how ∆l varies with m, the mass added to the hanger.

Determine the mass added to the hanger shown in diagram above.

[1 mark]

She places Q between the jaws of the callipers and records the reading indicated.

Without pressing the zero button she removes Q and closes the jaws.

Views of the callipers before and after she closes the jaws are shown below:

Calculate the true diameter of Q.

[1 mark]

(d) The original length of Q was 1.82 m.

Determine the Young modulus of the metal in Q.

[4 marks]

(e) Lexy repeats her experiment using a wire of the same original length and metal but with a smaller diameter.

Discuss two ways this change might affect the percentage uncertainty in her result for the Young modulus.

[4 marks]

(Total 11 marks)