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qUESTIONS

A small-blackened solid copper sphere of radius 2.5 cm is placed in an evacuated chamber. The temperature of the chamber is maintained at 100 °C. At what rate energy must be supplied to the copper sphere to maintain its temperature at 110 °C? (Take Stefan’s constant σ to be 5.76 x 10² s⁻¹ K² and treat the sphere as blackbody.)

Find the temperature of a blackbody if its spectrum has a peak at (a) A = 700nm (visible), (b) A =3 cm (micro wave region) and (¢) A = 3 m (FM radio waves) (Take Wien’s constant b = 2.897x 107 m K).

Earth’s mean temperature can be assumed to be 280 K. How will the curve of blackbody radiation look like for this temperature? Find out λmax . In which part of the electromagnetic spectrum, does this value lie?

Compare the rates of emission of heat by a blackbody maintained at 727 °C and at227°C, if the blackbodies are surrounded by an enclosure (black) at 27 °C. What would be the ratio of their rates of loss of heat ?

The emissive power of a sphere of area0.02 m? is 0.5 kecal s’ m™. What is the amount of heat radiated by the spherical surface in 20 second?

Energy iis emitted from a hole in an electric furnace at the rate of 20 W, when the temperature of the furnace is727 °C. What is the area of the hole?(Take Stefan’s constant ¢ to be 5.7 x10*F s w2 K)

Calculate the energy radiated in one minute by a blackbody of surface area100 cm? when it is maintained at 227°C.

Assuming that the temperature at the surface of the Sun is 6000 K, find out the size of a virtual star (in terms of the size of Sun) whose surface temperature is 3000K and the power radiated by the virtual star is 25 times the power radiated by the Sun.Treat both, the Sun and virtual star as a blackbody.

Compare the rate of loss of heat from a metal sphere at 827 °C with the rate of loss of heat from the same sphere at 427 °C, if the temperature of the surroundingw27 °C.

A 60 watt filament lamp loses all its energy by radiation from its surface. The emissivity of the surface is 0.5. The area of the surface is 5 x 10° m? Find the temperature of the filament(o =5.67 x 10*]m²s⁻¹K²x² )

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