Q. A metal sphere of surface area 0.0225 m² is in an evacuated enclosure whose walls are held at a very low temperature. Electric current is passed through resistors imbedded in the sphere causing electrical energy to be dissipated at the rate of 75 W. If the sphere surfaces temperature is measured to be 560 K, while in steady state, calculate emissivity of the sphere surface

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Q. The Stefan-Boltzmann constant has units of

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Q. According to Stefan-Boltzmann law of thermal radiation

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Q. Calculate the radiant flux density from a black surface at 400 degree Celsius?

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Q. If the emitted radiant energy is to be doubled, to what temperature surface of black body needs to be raised? Take radiant flux density as 11631.7 W/m 2.

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Q. A furnace having inside temperature of 2250 has a glass circular viewing of 6 cm diameter. If the transmissivity of glass is 0.08, make calculations for the heat loss from the glass window due to radiation

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Q. The value of radiation coefficient or the Stefan-Boltzmann constant is

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Q. What is the wavelength band for Ultraviolet rays?

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Q. A black body of total area 0.045 m² is completely enclosed in a space bounded by 5 cm thick walls. The walls have a surface area 0.5 m² and thermal conductivity 1.07 W/ m K. If the inner surface of the enveloping wall is to be maintained at 215 degree Celsius and the outer wall surface at 30 degree Celsius, calculate the temperature of the black body

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Q. What is the wavelength band for solar radiation?

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Q. The relationship (Wavelength)MAX T = constant, between the temperature of a black body and the wavelength at which maximum value of monochromatic emissive power occurs is known as

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Q. A body at 500 K cools by radiating heat to ambient atmosphere maintained at 300 K. When the body has cooled to 400 K, the cooling rate as a percentage of original rate is about

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Q. Two spheres A and B of same material have radius 1 m and 4 m, and temperatures 4000 K and 2000 K respectively. Then the energy radiated by sphere A is

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Q. A small body has a total emissive power of 4.5 kW/m². Determine its surface temperature of maximum emission

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Q. A small black body has a total emissive power of 4.5 k W/m². In which range of the spectrum does this wavelength fall?

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Q. The sun emits maximum radiation of 0.52 micron meter. Assuming the sun to be a black body, Calculate the surface temperature of the sun

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Q. A furnace emits radiation at 2000 K. Treating it as a black body radiation, calculate the wavelength at which emission is maximum

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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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