An aluminium measuring rod, which is correct at `5^(@)C` measures the length of line as 80 cm at `45^(@)C`. If thermal coefficient of linear expansion of aluminium is `2.50xx10^(-5)per.^(@)C`. The correct length of the line is

Options

A. 80.08 cm
B. 79.92 cm
C. 81.12 cm
D. 79.62 cm

Answer

A

Explanation

The 80 cm mark on the aluminium rod is really at a greater distance fron the zero position than indicated because of the increase in temperature `Deltatheta=40^@C`. The increase Length is
`DeltaL=alpha_(A1)L_(A1)Deltatheta`
`=(2.50xx10^-5)(80)(40)`
`=0.08cm`
The correct length of the line is
`L=80+0.08=80.08cm`