Question

Two rods P and Q of same length and same diameter having thermal conductivity ratio 2 : 3 joined end to end. If temperature at one end of P is 100°C and at one and of Q 0°C, then the temperature of the interface is (a) 40°C (b) 50°C (c) 60°C (d) 70°C

Answer 1

Let the temperature of interface of both the rod is T.

So heat flow rate will be:

t

Q

=

L

KAΔT

So heat will flow from higher temperature to lower, hence at steady state we equate both of them to find the common intermediate temperature T.

L

K

p

(100−T)

=

L

K

q

(T−0)

It is given that:

K

q

K

p

=

3

2

So, on putting in above equation we

3

2

(100−T)=T

⇒T=40

0

C

Answer 2

Answer:

40 °C

Explanation:

Let the temperature of interface of both the rod is T.

So heat flow rate will be:

t Q = L KAΔT

So heat will flow from higher temperature to lower, hence at steady state we equate both of them to find the common intermediate temperature T.

L Kp (100−T) = l K q (T−0)

It is given that:

K q K

p = 3 2

So, on putting in above equation we

3 2(100−T)=T

⇒T=40 ° C