1.

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 ?

Answer»

`3:4`
`4:3`
`2:3`
`4:1`

Solution :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).


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