Two insulated metal bars each of length 5 cm and rectangular cross section with sides 2 cm and 3 cm are wedged between two walls, one held at `100^@C` and the other at `0^@C`. The bars are made of lead and silver. `K_(pb)=350 W//mK,K_(Ag)=425 W//mK`.
Total thermal current through the two bar system is

Options

A. 210 W
B. 420 W
C. 510 W
D. 930 W

Answer

D

Explanation

Resistance of silver bar
`R_(Ag)=(l_Ag))/(K_(Ag)A_(Ag))=(5xx10^-2)/(425xx6xx10^-4)`
`=(100)/(85xx6)=(20)/(17xx6)=(10)/(51)(K)/(W)`
Thermal current through silver bar
`I_(Ag)=(DeltaT)/(R_(Ag))=(100xx51)/(10)=510W`
Total thermal current `I_(pb)+I_(Ag)=930W`