Two identical rectangular rods of metal are welded end to end in series between temperature `0^(@)C` and `100^(@)C and 10 J` of heat is conducted (in steady state process) through the rod in `2.00 min.` if `5` such rods are taken and joined as shown in figure maintaining the same temperature difference between A and B, then the time in which `20 J` heat will flow through the rods is

Options

A. `30 sec`
B. `2 min`
C. `1 min`
D. `20 sec`

Answer

C

Explanation

`(dQ)/(dt) = (KA Delta T)/(2l) = (Delta T)/(2l) = (10)/(12) J//sec`.
New rate `(dQ)/(dt) = (Delta T)/((l)/(2Ka)) = 40/120 J//sec,`
So time taken is `t=20/40 xx 120 sec. = 60 sec`
.