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5BANSAL CLASSES
B Target IIT JEE 2007 CLASS : XI (PQRS) DATE: 17/12/2005
PHYSICS Daily Practice Problems MAX.TIME: 60 Min. DPP. NO.-82
Q.l
A spherical black body with a radius of 12 cm radiates 450W power at 500K. If the radius were halved and the temperature doubled, the power radiated in watts would be
Q. 2
The temperature of blackbody is increased by 1%. The amount of radiation emitted by it increases by
Q. 3
A sphere, a cube and a thin circular plate are heated to the same temperature. If they are made of same material and have equal masses then determine which ofthese three objects cools the fastest and which one cools the slowest?
Q.4
The energyradiatedby a black body at 2300 K isfoundto have the maximum at a wavelength 1260 nm, its emissive power being 8000 WITT2. When the body is cooled to a temperature T K, the emissive power is found to decrease to 500 Wnr 2 . Find: the temperature T the wave length at which intensity of emission in maximum at the temperature T.
(i) (ii) Q.5
At a temperature T,, a body radiates maximum energy corresponding to a wavelength of3000 A. On increasing its temperature to T2, the maximum energy is radiated for wavelength of 2000 A. The surroundings are at 300 K, if the rate of loss of energy by the body at temperature T2 is 6 times that at temperature T,, find the temperatures Tj and T2.
Q.6
A cylinder fitted with a metal piston contains water and steam at constant temperature as in fig. The cross-sectional area of the cylinder is 2.5 cm2. The piston is falling at a rate of 0.25 cm/sec. The density of steam under the piston is 6.0 x lO^gm/cm3. Find the rate of condensation of steam the rate with which heat is leaving the chamber. (L v = 2.25 x 106 J/kg)
(i) (ii)
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Q.7
A body cools from 50째 C to 40째C in 5 minutes. The surrounding temperature is 20째C. What will be its temperature 5 minutes after reading 40째C? Use approximate method.
Q. 8
A solid copper sphere (density p, specific heat C) ofradius r at an initial temperature 200 K is suspended inside a chamber whose walls are at almost 0 K. Calculate the time required for the temperature of the sphere to drop to 100K. Neglect the effect of thermal contraction.
Q. 9
The solar constant for a planet is S. The surface temperature of the sun is T K. The sun subtends an angle 9 at the planet. Find S. [Note: Solar constant is rate at which radiations are received from sun per unit surface area]
Q. 10 A highly conducting solid sphere of radius R, density p and specific heat s is kept in an evacuated chamber. A parallel beam of electromagnetic radiation having uniform intensity I is incident on its surface. Assuming surface of the sphere to be perfectly black and its temperature at t = 0 to be equal to T0, Calculate maximum attainable temperature of the sphere. (Stefan's constant=a)