Q. No.In heat transfer, which method is based on gravitation ?
(1) Natural convection
(2) Conduction
(3) Radiation
(4) Stirring of liquids
(1) Natural convection
When fluids are heated from the bottom, convection currents are produced because -
(1) Molecular motion of fluid becomes aligned
(2) Molecular collisions take place within the fluid
(3) Heated fluid becomes more dense than the cold fluid above it
(4) Heated fluid becomes less dense than the cold fluid above it
If a liquid is heated in weightlessness, the heat is transmitted through
(1) Conduction
(2) Convection
(3) Radiation
(4) Neither, because the liquid cannot be heated in weightlessness
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:
| 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. |
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. |
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
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