Q.

A brass wire of length 2 m and radius 1 mm at 27°C is held taut between two rigid supports. Initially, it was cooled to a temperature of -43°C creating a tension T in the wire. The temperature to which the wire has to be cooled in order to increase the tension in it to 1.4T, is _________ C.               [2026]

1 - 80  
2  - 65  
3 - 71  
4 - 86  

Ans.

(3)

T=αYA(27-(-43))          ...(i)

1.4T=αYA(27-θ)             ...(ii)

Using (ii)/(i):

1.4=27-θ70

27-θ=98    θ=-71°C