The resistance of a copper wire and an iron at `20^@C` are `4.1 Omega` and `3.9Omega` respectively. Neglecting any thermal expansion, find the temperature at which resistane of both are equal.
`alpha_(Cu)=4.0xx10^-3K^-1` an `alpha_(Fe)=5.0xx10^-3K^-1`

Answer

A, B

Explanation

`R_1+R-2=20`…………i
`alpha_(eq)=(R_1alpha_1+R_2alpha2)/(R_1+R_20)`
`0=(R_1(-0.5xx10^-3)+R_2(5.0xx10^-3))/20`
`:. R-1=10R_2`………..ii
Solving eqn i and i we get
`R-2=R_(Fe)=20/11 Omega`
`=1.82Omega`
`R_1=R_(Cu)`
`=10R_2`
`=18.18Omega`