Q. The emissivity and the absorptivity of a real surface are equal for radiation with identical temperature and wavelength. This law is referred to as

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Q. With an increase in wavelength, the monochromatic emissive power of a black body

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Q. The temperature of a solid surface changes from 27 K to 627 K. The emissive power changes would then confirm to the ratio

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Q. If the temperature of a hot body is increased by 50%, the amount of radiations emitted by it would increase by nearly

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Q. Consider two bodies, one absolutely back and the other non-black and let these be at same temperature. Which one of the following statement is correct?

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Q. When Stefan-Boltzmann law is applied to a black body, it takes the form

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Q. When the emissivity of non-black surface is constant at all temperatures and throughout the entire range of wavelength, the surface is called

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Q. The emissivity of the gray surface may be expressed as

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Q. If a black body at 1000 K and a gray body at 1250 K emit the same amount of radiation, what should be the emissivity of the gray body?

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Q. The radiant heat transfer from a plate of 2.5 cm² area at 1250 K to a very cold enclosure is 5.0 W. Determine the emissivity of the plate at this temperature

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Q. A 100 W light bulb has a tungsten filament (emissivity = 0.30) which is required to operate at 2780 K. If the bulb is completely evacuated, calculate the minimum surface area of the tungsten filament

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Q. For a hemisphere solid angle is measured as

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Q. A gray body (E = 0.8) emits the same amount of heat as a black body at 1075 K. Find out the required temperature of the gray body

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Q. The heat energy absorbed by a known area in a fixed time is determined with the help of an instrument called

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Q. The value of solar constant varies between

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Q. The total amount of heat energy received by the sphere of radius r is

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Q. Amount of heat energy radiated by unit surface of the sun in the same time workout as
Take, R = mean distance of earth from the sun and r = radius of sun

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Q. Temperature of sun can be workout from

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Q. The temperature of the photosphere, referred to as the effective temperature of the sun, is usually taken as

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Q. The approximate distribution of the flow of sun’s energy to the earth’s surface is

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