Question

Two rods are of same material and having same length and area. If heat `DeltaQ` flows through them for 12 min when they are joined side by side. If now both the rods are joined in parallel, then the same amount of heat `DeltaQ` will flow in
A. 24 min
B. 3 min
C. 12 min
D. 6 min

Answer 1

Correct Answer - B
Let R = thermal resistance of each rod.
In first case, `R_("net") = R + R = 2R` (in series)
In second case, `R_("net") = R/2` (in parallel)
In second case thermal resistance has become `1/4 th.`
So, heat current will become 4 times. So time
taken to flow same amount of heat will be reduced
to `1/4th`.