Two rods of same length and transfer a given amount of heat 12 second, when they are joined as shown in figure (i). But when they are joined as shwon in figure (ii), then they will transfer same heat in same conditions in

Options

A. 24 s
B. 13 s
C. 15 s
D. 48 s

Answer

D

Explanation

As we use
`(Q)/(t)=(kA(DeltaT))/(L)`
`implies (Q)/(12)=(k(2A)(DeltaT))/(L)` ...(1)
Let in second condition, same heat is transfered in t seconds,
`(Q)/(t)=(k(A)(DeltaT))/(2L)`.....(2)
Dividing (1) by (2), we get
`(Q)/(12)xx(t)/(Q)=(k(2A)(DeltaT))/(L)xx(2L)/(k(A)(DeltaT))=4`
`t=12xx4=48s`