Home
Class 11
PHYSICS
Area of surface of a person is "1.9 m"^(...

Area of surface of a person is `"1.9 m"^(2)` and its body temp. is `37^(@)C` and room temp. is `22^(@)C`. Temperature of skin is `28^(@)C`, then find the rate of emission of heat. Emissivity of skin is `0.97`.

Text Solution

Verified by Experts

Rate of energy emission of body,
`H=Aesigma(T^(4)-T_(S)^(" 4"))" "T=273+28=301K`
`" "T_(S)=273+22=295K`
`1.9xx0.97xx5.67xx10^(-8)[(301)^(4)-(295)^(4)]`
`=10.44981xx[8208541201-7573350625]xx10^(-8)`
`=10.44981xx635190576xx10^(-8)`
`=66.37620832`
`~~66.4W`
This rate is greater than half of rate of energy produced on body (120 W) under thermal steady state.
To decrease this loss, in modern arctic clothes, there is a small smooth excessive metal layer which reflects the emitter energy from body hence loss decreases.
Promotional Banner

Topper's Solved these Questions

  • THERMAL PROPERTIES OF MATTER

    KUMAR PRAKASHAN|Exercise Try Yourself (VSQs)|84 Videos

  • THERMAL PROPERTIES OF MATTER

    KUMAR PRAKASHAN|Exercise Information : Higher Order Thinking Skills (HOTS)|8 Videos

  • SYSTEMS OF PARTICLES AND ROTATIONAL MOTION

    KUMAR PRAKASHAN|Exercise SECTION-F (SECTION-D) QUESTIONS PAPER|1 Videos

  • THERMODYANMICS

    KUMAR PRAKASHAN|Exercise Question Paper|11 Videos

Similar Questions

Explore conceptually related problems

A 10 g ice cube is dropped into 45 g of water kept in a glass. If the water was initially at a temperature of 28^(@)C and the temperature of ice -15^(@)C , find the final temperature (in ^(@)C ) of water. (Specific heat of ice =0.5" "cal//g-""^(@)C" and "L=80" "cal//g)

2g ice at 0^(@)C is mixed with 1 g steam at 100^(@)C . Find the final temperature of the mixture.

Two plates of equal areas are placed in contact wih each other. Their thickness are 2.0 cm and 5.0 cm respectively. The temperature of the external surface of the first plate is -20^(@)C and that of the external surface of the second plate is 20^(@)C . What will be the temperature of the current surface if the plates (i) are of the same material, (ii) have thermal conductivities in the ratio 2:5 .

A closed cubical box is made of perfectly insulating material and the only way for heat to enter or leave the box is through two solid cylindrical metal plugs, each of cross sectional area 12cm^(2) and length 8cm fixed in the opposite walls of the box. The outer surface of one plug is kept at a temperature of 100^(@)C . while the outer surface of the plug is maintained at a temperature of 4(@)C . The thermal conductivity of the material of the plug is 2.0Wm^(-1).^(@)C^(-1) . A source of energy generating 13W is enclosed inside the box. Find the equilibrium temperature of the inner surface of the box assuming that it is the same at all points on the inner surface.

What is the temperature of the steel-copper junction is the steady state of the system shown in figure. Length of the steel rod = 15.0 cm, length of the copper rod = 10.0 cm, temperature of the furnace =300^(@)C , temperature of the other end =0^(@)C . The area of cross section of the steel rod is twice that of the copper rod. (Thermal conductivity of steel =50.2" Js"^(-1)m^(-1)K^(-1) , and copper =385" Js"^(-1)m^(-1)KJ^(-1) ).

Temperature of body A of 0.5 to mass is 60^(@)C Temperature of body B of 0.3 kg mass is 90^(@)C . If both are joined by conducting rod, then heat . . . . . . . Specific heat of A is 0.85 J/gm K Specific heat of B is 0.9 J/gm K

A carbot freezer takes heat from water at 0^(@)C inside it and rejects it to the room at a temperature of 27^(@)C . The latent heat of ice is 336xx10^(3)Jkg^(-1) . If 5kg of water at 0^(@)C is converted into ice at 0^(@)C by the freezer, then the energy consumed by the freezer is close to :

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.

At room temperature (27.0^(@)C) the resistance of a heating element is 100 Omega. What is the temperature of the element if the resistance is found to be 117 Omega. given that the temperature coefficient of the material of the resistor is 1.70 xx 10 ^(-4)"" ^(@)C^(-1).

A stone of 0.36 m^(2) cross -sectional area and 0.1 m thickness has its lower surface in contact with water at 100^(@)C and upper surface in contact with ice at 0^(@)C . If 4.8 kg ice melting in 1 hour, then what is the thermal conductivity of stone ? Latent heat of fusion of ice is 3.36xx10^(5)" J/kg" .