Practice MCQ Questions and answers on Physics-GK

Refrigeration is the process by which artificial cooling takes place. The temperature is kept lower than the normal during the process. It stops the growth of the bacteria thereby keeping the food perishable and edible.

When air is blown with open mouth, its pressure is same as that of atmospheric pressure since it is in direct contact with atmosphere. Hence it is an isobaric process.

Joule effect is not reversible.

The diesel engine gains its energy by burning fuel injected or sprayed into the compressed, hot air charge within the cylinder. The air must be heated to a temperature greater than the temperature at which the injected fuel can ignite.

Convection transfers heat vertically into the atmosphere. In order for heat to be transferred to other regions, it must be transferred horizontally by the wind. The horizontal transfer of heat by the wind is called advection. Advection is a transport mechanism of a substance or conserved property by a fluid due to the fluid’s bulk motion. An example of advection is the transport of pollutants or silt in a river by bulk water flow downstream.

The 1st law of thermodynamics states that internal energy change of a system equals net heat transfer minus net work done by the system.

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

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.

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

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.