A meter-scale is made of copper and iron rods as shown in the figure. If the length of copper rod is `lambda` meter and the coefficients of linear expansion of copper and iron are `a_(1)` and `a_(2)` respectively, then the equvalent coefficient of linear expansin of the combined material of the meter-scale is

Options

A. `(lambda a_(1)+a_(2))/(lambda+1)`
B. `(a_(1)+lambda a_(2))/(lambda+1)`
C. `sqrt(lambdaa_(1)a_(2))`
D. `lambdaa_(1)+(1-lambda)a_(2)`

Explanation

`Delta l=Delta l_(1)+Deltal_(2)`
`alpha_(eq)DeltaT=lambdaalpha_(1)DeltaT+(1-lambda)alpha_(t)DeltaT`