Three rods of the same dimension have thermal conductivities 3K, 2K and K. They are arranged as shown in fig. Given below, with their ends at `100^(@)C, 50^(@)C` and `20^(@)C`. The temperature of their junction is :-

Options

A. `60^@C`
B. `70^@C`
C. `50^@C`
D. `35^@` C

Answer

B

Explanation

H `rarr` heat current
Since,
`H=H_1+H_2`

`implies (3KA(100-T))/(l)=(2KA(T-50))/(l)+(KA(T-20))/(l)`
`implies T=70^@C`