Physics - Study Mode

[#241] Which phase change is an example of an exothermic process?
Correct Answer

(D) All the above

Explanation

Solution: Processes that require or give off heat will be limited to changes of state, known as phase changes, and changes in chemical constitution, or chemical reactions. Changes of state involve a solid melting, a liquid freezing, a liquid boiling or a gas condensing. An exothermic process is one that gives off heat, which is transferred to the surroundings. An endothermic process is a reaction which heat has to be supplied to the system from the surroundings. Here in all the given options, heat is taken away from them to change there phase. Liquid to Solid --- Freezing Gas to Liquid --- Condensation Gas to Solid --- Deposition are all examples of exothermic processes

[#242] The velocity of heat radiation in vacuum is
Correct Answer

(A) Equal to that of light

Explanation

Solution: Electrons are generally responsible for heat conduction. The phonons (vibrations of the nuclei) also play a part, depending on the temperature of the medium. It depends on the specific conductor you’re using. At some point, in a vacuum, the electrons have to be excited enough to spit out photons, which are Electromagnetic radiation, which in a vacuum should go on forever at the speed of light theoretically.

[#243] In a Carnot engine when heat is taken from the source, its temperature
Correct Answer

(A) Remains constant

Explanation

Solution: In a Carnot engine when heat is taken from the source, its temperature remains constant.

[#244] Even after sunset, the air near the Earth's surface continue to receive heat due to
Correct Answer

(B) Terrestrial Radiation

Explanation

Solution: Even after the sunset when the sun goes down, the incoming radiation from the sun stops, but there is still a lot of radiation that has been absorbed by the earth, which is re-radiated in form of terrestrial radiation.Energy leaving the earth’s surface i.e. terrestrial radiation heats up the atmosphere more than the incoming solar radiation i.e. insolation.

[#245] Which of the following represents a relation for ''heat lost = heat gained'?
Correct Answer

(C) Principle of calorimetry

Explanation

Solution: The answer is calorimetry, calorimetry is the principle used in calorimeters according to this the net rate of heat generated is same as heat gained by the cooling mechanism. Since there is no work transfer it is relevant.