Ratio of thermal conductivities of two different materials is `4:3` To have same thermal resistance of the two rods of having equal thickness, what should be the ratio of their lengths ?

Options

A. `3:4`
B. `4:3`
C. `2:3`
D. `4:1`

Answer

B

Explanation

Thermal resistance `R=(l)/(kA)`
`:.R_(1)=R_(2).(l_(1))/(k_(1)A_(1))=(l_(2))/(k_(2)A_(2))`
Here `A_(1)=A_(2)` as thickness is same.
`:.(l_(1))/(l_(2))=(k_(1))/(k_(2))=4/3`.
Thus correct choice is (b).