Q.

A force is applied to a steel wire ‘A’, rigidly clamped at one end. As a result, elongation in the wire is 0.2 mm. If the same force is applied to another steel wire ‘B’ of double the length and a diameter 2.4 times that of the wire ‘A’, the elongation in the wire ‘B’ will be (wires having uniform circular cross sections).         [2023]

1 6.06×10-2 mm  
2 2.77×10-2 mm  
3 3.0×10-2 mm  
4 6.9×10-2 mm  

Ans.

(4)

Y=F/AΔll

F=YAlΔl

(AΔll)1=(AΔll)2

Δl2Δl1=A1A2×l2l1

Δl20.2=12.4×2.4×21

Δl2=6.9×10-2 mm