1. Experiment to determine Young’s Modulus of a steel wire

2. Searle’s Apparatus

3. Searle’s Apparatus
Searle’s apparatus is a device used to accurately determine the Young Modulus of a metal wire.
It has two wires, one that will be stretched and one control.

5. Using a Micrometer Reading/m m Highest number along the datum line 10
10.00
the next line along datum line is not yet uncovered
so the final reading is less than 11 mm
Reading on thimble
16 0
0.16
Uncorrected reading
10.16
Zero error (below zero) -2
0.02
Corrected reading (add zero error)
10.18

6. To calculate the Young Modulus we need:

7. Searle’s apparatus consists of two metallic frames suspended from a rigid support with the help of experimental wire, (whose Young’s modulus is to be determined) and compensating wire.
The slotted weights can be slipped to the hanger so as to load the experimental wire to a desired value. In order to keep the compensating wire tight, a fixed weight i.e. dead weight is used.
A spirit level is mounted between two frames. Its one end rests on the tip of the screw of the spherometer. When the screw of the spherometer is turned, it moves against a vertical scale graduated in mm.
To find Young’s modulus, the bubble in the spirit level is brought exactly at its centre. So the spherometer screw is moved upward. The distance through which the screw has to be moved, is noted which gives the extension in the wire. Let L be length and r, the radius of the wire, then Young’s modulus of the material of wire.

8. Limit of proportionality = straight part of graph
Elastic limit = point until which, material behaves elastically.
These two don’t always coincide.