Question

Temperature of a room is maintained at ${20}^{\circ }$ by a heater of power $2kW$. The room has a glass window of area $1m^2$, thickness $0.2cm$ and thermal conductivity $0.2cal/m{/}^{\circ }C/s$. Temperature of outside is about.

• A. $-{63.6}^{\circ }C$
• B. ${15}^{\circ }C$
• C. ${20}^{\circ }C$
• D. ${12}^{\circ }C$

Answer 1

The correct option is A $-{63.6}^{\circ }C$

If temperature of outside be $\theta$ then putting $k=0.2,A=1m^2,l=.002meter$

and $H=2kW=2000J/s=2000\times 4.18cal/s=8360cal/s$

in the formula $H=KA\frac{20-\theta }{l}$, we get $20-\theta ={83.6}^{0}C$

so $\theta =-{63.6}^{0}C$