Q. Four identical pieces of copper painted with different colors of paints were heated to the same temperature and then left in the environment to cool. Which of the following paint will give fast cooling?

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Q. A surface for which emissivity is constant at all temperatures and throughout the entire range of wavelength is called

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Q. If radiant energy EB emitted by the black surface strikes the non-black surface. If non-black surface has absorptivity α, it will absorb how much radiations?

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Q. If two surfaces are at the same temperature, then the conditions correspond to mobile thermal equilibrium for which the resultant interchange of heat is zero are

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Q. The absorptivity of black body equals to

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Q. A diathermanous body

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Q. Choose the false statement

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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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