The rate of loss of heat from a body cooling under conditions of forced convection is proportional to its (A) heat capacity (B) surface area (C) absolute temperature (D) excess of temperature over that of surrounding : state if

(1) A, B, C are correct               

(2) Only A and C are correct

(3) Only B and D are correct     

(4) Only D is correct

Subtopic:  Convection |
From NCERT
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In which of the following process, convection does not take place primarily ?

(1) Sea and land breeze

(2) Boiling of water

(3) Warming of glass of bulb due to filament

(4) Heating air around a furnace

 

Subtopic:  Radiation |
 72%
From NCERT
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On a clear sunny day, an object at temperature T is placed on the top of a high mountain. An identical object at the same temperature is placed at the foot of the mountain. If both the objects are exposed to sun-rays for two hours in an identical manner, the object placed on the top of a mountain will register a temperature:

1. higher than the object at the foot.
2. lower than the object at the foot.
3. equal to the object at the foot.
4. none of the above.

Subtopic:  Radiation |
 52%
From NCERT
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Heat travels through vacuum by 
(1) Conduction                 

(2) Convection

(3) Radiation                     

(4) Both (a) and (b)

Subtopic:  Radiation |
 80%
From NCERT
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Taking into account the radiation that a human body emits which of the following statements is true?

1. The radiation is emitted only during the day.
2. The radiation is emitted during the summers and absorbed during the winters.
3. The radiation emitted lies in the ultraviolet region and hence is not visible.
4. The radiation emitted is in the infra-red region.
Subtopic:  Radiation |
 59%
From NCERT
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The earth radiates in the infra-red region of the spectrum. The spectrum is correctly given by

(1) Wien’s law                               

(2) Rayleigh  law

(3) Planck’s law of radiation             

(4) Stefan’s law of radiation

Subtopic:  Radiation |
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Pick out the statement which is not true .

(1) IR radiations are used for long distance photography

(2) IR radiations arise due to inner electron transitions in atoms

(3) IR radiations are detected by using a bolometer

(4) Sun is the natural source of IR radiation

Subtopic:  Radiation |
From NCERT
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A hot and a cold body are kept in vacuum separated from each other. Which of the following cause decrease in temperature of the hot body ?

(1) Radiation

(2) Convection

(3) Conduction

(4) Temperature remains unchanged

Subtopic:  Radiation |
 82%
From NCERT
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For a perfectly black body, its absorptive power is

(1) 1                 

(2) 0.5

(3) 0                 

(4) Infinity

Subtopic:  Radiation |
 84%
From NCERT
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Certain substance emits only the wavelengths λ1, λ2, λ3 and λ4 when it is at a high temperature. When this substance is at a colder temperature, it will absorb only the following wavelengths ?
(a) λ1                      (b) λ2
(c) λ1 and λ2          (d)  λ1, λ2, λ3 and λ4

Subtopic:  Radiation |
 81%
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