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qUESTIONS

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 )

Calculate the energy radiated in one minute by a blackbody of surface area 200 cm² at 127 °C ( σ = 5.7 x 10Jm²s⁻¹K).

Calculate the value of λmax for solar radiation assuming that surface temperature of Sun is 5800 K(b=2.897 x103m K). In which part of the electro magnetic spectrum, does this value lie ?

Calculate the average molecular kinetic energy (i) per kmol (ii) per kg (iii) per molecule of oxygen at 127 °C, given that molecular weight of oxygen is 32, R is 8.31 J mol K-¹ and Avogadro’s number N is 6.02 * 10² 23 molecules mol-¹.

Find kinetic energy of 5 litre of a gas at S.T.P. given standard pressure is 1.013 × 105 N/m².

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