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

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

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:

Heat travels through vacuum by 
(1) Conduction                 

(2) Convection

(3) Radiation                     

(4) Both (a) and (b)

Taking into account the radiation that a human body emits which of the following statements is true?

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

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

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

For a perfectly black body, its absorptive power is

(1) 1                 

(2) 0.5

(3) 0                 

(4) Infinity

Certain substance emits only the wavelengths ${\mathrm{\lambda }}_1, {\mathrm{\lambda }}_2, {\mathrm{\lambda }}_3$ and ${\mathrm{\lambda }}_4$ when it is at a high temperature. When this substance is at a colder temperature, it will absorb only the following wavelengths ?
(a) ${\mathrm{\lambda }}_1$                      (b) ${\mathrm{\lambda }}_2$
(c) ${\mathrm{\lambda }}_1$ and ${\mathrm{\lambda }}_2$          (d)  ${\mathrm{\lambda }}_1, {\mathrm{\lambda }}_2, {\mathrm{\lambda }}_3$ and ${\mathrm{\lambda }}_4$