\hat is Young's modulus?
Describe an experiment to find out Young's modulus of material in the form of a long string wire.
(3 marks question)
Answers
Materials Required
Searle’s apparatus
Two long steel wires of same length and diameter
A metre scale
A set of 1/2 Kg slotted weights
1 Kg weight hanger
1 Kg dead load.
The Procedure
Two wires of the same material, length and diameter have their ends tightened in torsion screws A,B, C and D as shown in Fig.
Wire AB becomes the experimental wire and CD becomes the auxiliary wire.
Suspend a 1 kg dead load from hook of frames F1 and F2.
The weight hanger at F1 is loaded and unloaded 3 or 4 times, so that the experimental wire AB comes under elastic mood.
Now, each wire has been loaded equally with 1 kg. The pitch and the least count of the spherometer are determined.
The central screw is adjusted in such a way that the air bubble in the spirit level is exactly at the centre. The head scale reading of the spherometer is noted for zero weight in the weight hanger attached to the frame F1.
A half kg of weight is now added to the weight hanger attached to the frame F1.
The air bubble moves away from the centre. The spherometer screw is adjusted so that the air bubble comes back to the centre. The spherometer reading is noted.
The load is increased in steps of half kg (maximum load should be less than the breaking stress) and the corresponding spherometer reading is noted.
The same procedure is repeated for unloading the weights in steps of half kg. From these observations the extension, l for a load M can be determined.
Young’s modulus can be calculated using the equation (3)
Simulator Procedure (as performed through the Online Labs)
Select the environment from the drop down list.
Select the material of the wire from the drop down list.
Change the radius of the wire using the slider.
Change the length of the wire using the slider.
Change the weight in the weight hanger using the slider.
Once the weight has been added to the weight hanger, the bubble in the sprit level moved to its extreme end.
Click on the right/left arrow button on the bottom right side to move the spherometer upward/downward to adjust the bubble to the center.
Note down the number of rotations and fractional rotations from the spherometer and the value from the scale.
Calculate the extension, l, of the wire form the values.
Calculate the Young’s modulus of the wire using the formula, Y = MgL/πr2l .
To verify your result click on the ‘Show result’ check box.
To redo the experiment, click on the ‘Reset’ button.
Our Observations:
To find the diameter of the wire using a screw gauge.
Distance moved by the screw for 4 rotations, x =………mm
Pitch of the screw, P =…………… mm
Number of divisions on the circular scale, N=.................
Least Count (L.C) of the screw gauge = =……………………….mm
Zero Correction, z =………………………..dvs
Slno PSR(mm) HSR(div) Corrected HSR=HSR+z(div) Total Reading=(PSR+(corrected HSR L.C))mm
Mean Diameter, d
Radius of the experimental wire, r = d/2 =.............mm = ……x 10-3m
Length of the experimental wire, L =………..cm =…………x10 -2m
How to find Load and Extension
Least count of Spherometer
1 pitch scale division = 1mm
Number of full rotations given to screw = 4
Distance moved by the screw for 4 rotations = 4mm
Hence, pitch, p= =1mm
Number of divisions on circular scale = 100
Hence least count= = 0.01 mm
SlNo Load on hanger,M(kg) Spherometer Screw reading Extension,l for a loadM=2 kg(mm)
On loading, x (mm) On unloading,y(mm) Mean,(mm)
0 z1
.5 z2
1 z3
1.5 z4
2 z5 z5-z1
2.5 z6 z6-z2
3 z7 z7-z3
3.5 z8 z8-z4
Mean extension, l
The Calculations :
Mean extension for 2 kg load, l = ……………x10-3m
Load, M = 2 kg
Young’s modulus,
= …………………………Nm-2
Result:
The Young’s modulus for the material of the wire as determined by Searle’s apparatus, Y = ………………Nm-2
Now, we’ll do the experiment…
Explanation:
- Two strings were hung from a support and two pans were attached to both the strings.
Weights are kept on both the pans.
- When the number of weights in second pan was increased, the string got stretched and moved in downward direction.
- The change in length was measured by the metre scale which was kept on reference wire.