Home
Class 11
PHYSICS
An electric heater is placed inside a r...

An electric heater is placed inside a room of total wall area `137 m^2` to maintain the temperature inside at `20^@C`. The outside temperature is `-10^@C`. The walls are made of three composite materials. The inner most layer is made of wood of thickness 2.5 cm the middle layer is of cement of thickness 1 cm and the exterior layer is of brick of thickness 2.5 cm. Find the power of electric heater assuming that there is no heat losses through the floor and ceiling. The thermal conductivities of wood, cement and brick are `0.125 W//m^@-C, 1.5W//m^@-C and 1.0 W//m^@-C` respectively.

Text Solution

Verified by Experts

The correct Answer is:
A, D
Three thermal resistance are in series. `(R_t = l/(KA))`
`:. R = R_1 + R_2 + R_3`
`= ((2.5 xx (10^-2))/(0.125 xx 137)) + ((1.0 xx (10^-2))/(1.5 xx 137)) + ((2.5 xx (10^-2))/(1.0 xx 137))`
`=0.0017^@C-s//J`
Now, heat current `H = ("Temperature difference")/("Net thermal resistance")`
`= (30/(0.0017)) = 17647 W` .
Promotional Banner

Topper's Solved these Questions

  • CALORIMETRY & HEAT TRANSFER

    DC PANDEY|Exercise Level 2 More Than One Correct|5 Videos

  • BASIC MATHEMATICS

    DC PANDEY|Exercise Exercise|13 Videos

  • CALORIMETRY AND HEAT TRANSFER

    DC PANDEY|Exercise Medical entrance s gallery|38 Videos

Similar Questions

Explore conceptually related problems

An electric heater is used in a room of total wall area 137m^(2) to maintain a temperature of +20^(@)C inside it when the outside temperature is -10^(@)C . The walls have three different layers materials . The innermost layer is of wood of thickness 2.5 cm, in the middle layer is od cement of thickness 1.0 cm and the outermost layer is of brick of thickness 25.0 cm. find the power of the electric heater. Assume that there is no heat loss through the floor and the ceiling. The thermal conductives of wood, cement and brick are 0.125, 1.5 and 1.0 watt//m// .^(@)C respectively.

An electric heatet is uesd in a room of total wall area 137m^(2) to maintain a temperature of 20^(@)C inside it, when the outside temperature is -10^(@)C .The wall have three different layers of matwerials. The innermost layer is of wood of thickness 2.5cm, the middle layer is of cement of thickness 1.0cm and the outermost layer is of brick of thickness 25.0cm. Find the power of the electric heater. Assume that there is no heat loss through the flooor and the celling. The thrermal conductivities of wood, cement and brick aree 0.125Wm^(-1) ^(@)C^(-1) , 1.5Wm^(-1) ^(@)C^(-1) . and 1.0Wm^(-1) ^(@)C^(-1) respectively.

A electric heater is placed inside a room of total wall area 137m^(2) and maintained at a temperature 20^(@)C inside, outside temperature -10^(@)C . The walls are made up of three composite materials. The innermost layer is made up of wood of thickness 2.5 cm, the middle layer is of cement of thickness 1 cm and the exterior layer is 25 cm thick. Assuming there is no loss of heat through any other way, the power of the electric heater is (the thermal conductivity of wood, cement and brick are "0.125 W m"^(2)""^(@)C^(-1),1.5Wm^(-2)""^(@)C^(-1) and 1Wm^(-2)""^(@)C^(-1) respectively)

An electric heater is used in a room of total wall area 150m^2 to maintain a temperature is -5^@C . The innermost layer is of wood of thichness 2.0 cm, the middle layer is of cement of thickness 1.0 cm and the outer-most layer is of brick of thickness 20 cm. Find the power of the electric heater. Assume heat to flow only through the walls. The thermal conductivities of wood, cement and brick are 0.150 , 0.175 and 1.0 W//m^(@C) , respectively.

An electric heater is used to maintain a temperature of 15^@C inside a room of total wall area 125 m". The outside temperature is -10^@C . The walls of the room are made of three different layers, innermost layer is made of wood of thickness 2 cm, middle layer is made of brick of thickness 20 cm and outermost layer is made of cement of thickness 2 cm. If there is no loss of heat through the floor and ceiling, find the power of heater. Take, thermal conductivities of wood, brick and cement as 0.125 Wm^(-1) ""^@C^(-1) , 1.0 Wm^(-1) ""^@C^(-1) " and " 1.5 Wm^(-1) ""^@C^(-1) , respectively.

Middle lamella is amorphous layer of cementing material. It is chiefly made up of

A hemispherical bowl is made of steel, 0.25 cm thick. The inner radius of the bowl is 5 cm. Find the outer curved surface area of the bowl.

A tank contains three layers of immiscible liquids. The first layer is of water with refractive index 4//3 and thickness 8cm. The second layer is of oil with refractive index 3//2 and thickness 9cm while the third layer is of glycerine with refractive index 2 and thickness 4cm. Find the apparent depth of the bottom of the container.