A copper ball 2cm in radius is heated in a furnace to `327^(@)C` .If its emissivity is 0.3 ,at what rate does it radiate energy?

A thin square steel plate 10 cm on a side is heated in a black smith's forge to temperature of 800^@C . If the emissivity is 0.60, what is the total rate of radiation of energy ?

An electric heater of surface area 200cm^2 emits radiant energy of 60 kJ at time interval of 1 min. Determine its emissive power. If its emissivity be 0.45, what would be the radiant energy emitted by a black body in one hour, identical to the electrical heater in all respects?

A copper block of mass 2.5 kg is heated in a furnace to a temperature of 500^(@)C and then placed on a large ice block. What is the maximum amount (approx.) of ice that can melt? (Specific heat copper = 0.39 J//g^(@)C heat of fusion of water = 335 J//g ).

A spherical ball of radius 1cm coated with a metal having emissivity 0.3 is maintained at 1000 K temperature and suspended in a vacuum chamber whose walls are maintained at 300 K temperature. Find rate at which electrical energy is to be supplied to the ball to keep its temperature constant.

A thin brass rectangular sheet of sides 10 cm and 5 cm is heated in a furnace to 500^(@) C and taken out. How much electric power is needed to maintain the sheet at this temperature ? Its emissivity is 0.25.

A metal ball of surface area 200 cm^(2) and temperature 527^(@)C is surrounded by a vessel at 27^(@)C . If the emissivity of the metal is 0.4, then the rate of loss of heat from the ball is (sigma = 5.67 xx10^(-8)J//m^(2)-s-k^(4))

Assertion : When an iron rod is heated in a furnace, the radiation emitted goes from a lower frequency to a higher frequency as the temperature increases. Reason : The energy of a quantum of radiation is proportional to its frequency.

A circular disc of radius 3 cm is being heated. Due to expansion, its radius increases at the rate of 0.05 cm/sec. Find the rate at which its area is increasing when radius is 3.2 cm.

The surface of a household radiator has an emissivity of 0.55 and an area of 1.5 m^(2) . (a) At what rate is radiation emitted by the radiator when its temperature is 50^(@)C ? (b) At what rate is the radiation absorbed by the radiator when the walls of the room are at 22^(@)C ? (c ) What is the net rate of radiation from the radiator? (stefan constant sigma = 6 xx 10^(-8)W//m^(2)-K^(4))

A black body, at a temperature of 227^@C , radiates heat at a rate of 20 cal m^(-2)s^(-1) . When its temperature is raised to 727^@C , the heat radiated by it in cal M^(-2)s^(-1) will be closest to