A wall has two layers A and B each made of different materials. the layer A is 10 cm thick and B is 20 cm thick. the thermal conductivity of A is thirce that of B. Under thermal equilibrium, temperature across the wall is 35 degree celcius. The difference of temperature across the layer A is a) 30 degree celcius. b) 14 degree celcius. c) 8.75 degree celcius. d) 5 degree celcius.

Swapnil Saxena
102 Points
11 years ago

If the walls are in series then the heat currents established in both thew walls should be equal.

Let the temp. at A=0(say) , B=35( to maintain the temp. difference of 35 b/w the walls) and T (say across the layer)

= dQ1/dt =dQ2/dt

= (3K)A(T-0) / 10 = (K)A(35-T) / 20

= (6K)A(T)= (K)A(35-T)

= (6K) = (35-T)

=>7T=35

=> T= 5 -----------(ans)

ankit singh
3 years ago

let the temp. at A=0(say) , B=35( to maintain the temp. difference of 35 b/w the walls) and T (say across the layer)

= dQ1/dt =dQ2/dt

= (3K)A(T-0) / 10 = (K)A(35-T) / 20

= (6K)A(T)= (K)A(35-T)

= (6K) = (35-T)

=>7T=35

=> T= 5 -----------(ans)