Question

A room is maintained at ${20}^{o}C$ by a heater of resistance 20 ohm connected to 200 volt mains. The temperature is uniform through out the room and heat is transmitted through a glass window of area $1m^2$ and thickness 0.2 cm. What will be the temperature outside? Given that thermal conductivity K for glass is 0.2 cal /m/ ${}^{0}C$ /sec and J = 4.2 J/cal

• A.
• B.
• C.
• D. None of the above

Answer 1

The correct option is A

Heat developed by the heater $H=\frac{V^2}{R}.\frac{t}{J}=\frac{(200{)}^2\times t}{20\times 4.2}$

Heat conducted by the glass $H=\frac{0.2\times 1\times (20-\theta )t}{0.002}$

Hence $\frac{(200{)}^2\times t}{20\times 4.2}=\frac{0.2\times (20-\theta )t}{0.002}\Rightarrow \theta ={15.24}^{o}C$