If the sun’s surface radiates heat at 6.3×107 Wm-2. Calculate the temperature of the sun assuming it to be a black body σ=5.7×10-8 Wm-2K-4
(a) 5.8×103 K              (b) 8.5×103 K
(c) 3.5×108 K              (d) 5.3×108 K

Concept Questions :-

Stefan-Boltzmann law
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The value of Stefan’s constant is 
(a) 5.67×10-8 W/m2-K4                       (b) 5.67×10-5 W/m2-K4
(c) 5.67×10-11 W/m2-K4                      (d) None of these

Concept Questions :-

Stefan-Boltzmann law
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Rate of cooling at 600K, if surrounding temperature is 300K is R. The rate of cooling at 900K is
(a) 163R                     (b) 2R
(c) 3R                         (d) 23R 

Concept Questions :-

Newton's law of cooling
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A black body of surface area 10 cm2 is heated to 127°C and is suspended in a room at temperature 27°C. The initial rate of loss of heat from the body at the room temperature will be 
(a) 2.99 W                (b) 1.89 W
(c) 1.18 W                (d) 0.99 W

Concept Questions :-

Stefan-Boltzmann law
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Two identical objects A and B are at temperatures TA and TB respectively. Both objects are placed in a room with perfectly absorbing walls maintained at temperatures T(TA>T>TB)The objects A and B attain temperature T eventually which one of the following is correct statement

(a) ‘A’ only emits radiations while B only absorbs them until both attain temperature

(b) A loses more radiations than it absorbs while B absorbs more radiations that it emits until temperature T is attained

(c) Both A and B only absorb radiations until they attain temperature T

(d) Both A and B only emit radiations until they attain temperature T

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When the body has the same temperature as that of surroundings

(a) It does not radiate heat

(b) It radiates the same quantity of heat as it absorbs

(c) It radiates less quantity of heat as it receives from surroundings

(d) It radiates more quantity of heat as it receives heat from surroundings

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The spectral energy distribution of star is maximum at twice temperature as that of sun. The total energy radiated by star is 

(a) Twice as that of the sun

(b) Same as that of the sun

(c) Sixteen times as that of the sun

(d) One sixteenth of sun

Concept Questions :-

Stefan-Boltzmann law
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A bucket full of hot water cools from 75°C to 70°C in time T1, from 70°C to 65°C in time T2  and from 65°C to 60°C in time T3, then 
(a) T1=T2=T3               (b) T1>T2>T3
(c) T1<T2<T3                (d) T1>T2<T3

Concept Questions :-

Newton's law of cooling
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Consider two hot bodies B1 and B2 which have temperatures 100°C and 80°C respectively at t=0. The temperature of the surroundings is 40°C. The ratio of the respective rates of cooling R1 and R2 of these two bodies at t=0 will be 
(a) R1:R2=3:2       (b) R1:R2=5:4
(c) R1:R2=2:3       (d) R1:R2=4:5

Concept Questions :-

Newton's law of cooling
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Newton's law of cooling is a special case of
(a) Stefan's law            (b) Kirchhoff's law
(c) Wien's law              (d) Planck's law

Concept Questions :-

Newton's law of cooling
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