A composite block is made of slabs A,B,C,D and E of different thermal conductivities (given in terms of a constant K and sizes (given in terms of length, L) as shown in the figure. All slabs are of same width. Heat 'Q' flows only from left to right through the blocks. Then in steady state

Options

A. Heat flow through slabs A and E is same
B. Heat flow through slab E is maximum
C. Temperature difference across slab E is smallest
D. Heat flow through C = heat flow through B + heat flow through D

Answer

ACD

Explanation

(A) At steady state, heat flow through A and E are same. So option (A) is correct and option (B) is incorrect.
(C ) `DeltaT=HxxR`, where H is heat current, `R=(L)/(KA)`
'H' is same for A and E but R is smallest for E. So temperature difference across slab E is smallest. So option (C) is correct.
(D) `H_(B)=(DeltaT)/(R_(B)),H_(C)=(DeltaT)/(R_(C))andH_(D)=(DeltaT)/(R_(D))`, From this option if . `H_(C)=H_(B)+H_(D)`
`rArr(1)/(R_(C))=(1)/(R_(B))+(1)/(R_(D))rArr(4K(2Lb))/(4L)=(3K(Lb))/(4L)+(5K(Lb))/(4L)`
which is true. Here b is the width of slab. Hence option (D) is also correct.