The diameter of a wire measured by a screw gauge of least count 0.001 cm is 0.08 cm. The length measured by a scale of least count 0.1 cm is 150 cm. When a weight of 100 N is applied to the wire, the extension in length is 0.5 cm, measured by a micrometer of least count 0.001 cm. The error in the measured Young's modulus is 109 N/m2. The value of is . (Ignore the contribution of the load to Young's modulus error calculation)
- 1.3
- 1.65
- 0.13
- 0.25
Answer
(2) 1.65
Solution
Y= F/A l/L= 4FL d2 l
Data in SI: F=100 N, L=1.5 m, d=0.08 cm=8 10-4 m, l=0.5 cm=5 10-3 m
Y= 4 100 1.53.1416 (8 10-4)2 5 10-3
= 6001.005 10-8
5.97 1010 N/m2
Fractional error (load ignored):
YY=2 dd+ LL+ ( l) l
=2 0.0010.08+ 0.1150+ 0.0010.5
=0.025+0.00067+0.002=0.02767
Y=0.02767 5.97 1010
1.65 109 N/m2
=1.65
Answer: (2)