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A room at 20^@C is heated by a heater of...

A room at `20^@C` is heated by a heater of resistence 20 ohm connected to 200 VV mains. The temperature is uniform throughout the room and the heati s transmitted through a glass window of area `1m^2` and thickness 0.2 cm. Calculate the temperature outside. Thermal conductivity of glass is `0.2 cal//mC^@` s and mechanical equivalent of heat is `4.2 J//cal`.

A

13.69°C

B

15.24°C

C

17.85°C

D

19.96°C

Text Solution

Verified by Experts

The correct Answer is:
B
Temperature of room is not changing with time , then rate of heat produced due to resistor equal the rate of heat current through window,
`rArr(V^(2))/(R)(1)/(J)=(kA(20-theta))/(l)`
`((200)^(2))/(20)xx(1)/(4.2)=(0.2xx1(20-theta))/(0.2xx10^(-2))rArrtheta=15.24^(@)C`
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