Practice MCQ Questions and answers on Physics-GK

The compressor is the motor (or engine) of the cooling system. It is normally at the bottom of the refrigerator in the back. The compressor runs whenever the refrigerator thermostat calls for cooling.

Basically, refrigeration system consists of devices that compress and expand refrigerant gas . When refrigerant gas is compressed it expels heat and when it is suddenly expanded, absorbs heat. A refrigerator (colloquially fridge) is a common household appliance that consists of a thermally insulated compartment and a heat pump (mechanical, electronic, or chemical) that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room. A vapour compression cycle is used in most household refrigerators, refrigerator– freezers and freezers. In this cycle, a circulating refrigerant such as R134a enters a compressor as low-pressure vapour at or slightly above the temperature of the refrigerator interior. The vapour is compressed and exits the compressor as high pressure superheated vapour. The superheated vapour travels under pressure through coils or tubes comprising the condenser, which are passively cooled by exposure to air in the room. The condenser cools the vapour, which liquefies. As the refrigerant leaves the condenser, it is still under pressure but is now only slightly above room temperature. This liquid refrigerant is forced through a metering or throttling device, also known as an expansion valve (essentially a pin-hole sized constriction in the tubing) to an area of much lower pressure.

Hydrogen being gaseous has highest entropy.

Thermodynamics is the branch of physics that deals with the relationships between heat and other forms of energy. In particular, it describes how thermal energy is converted to and from other forms of energy and how it affects matter.

Heat is a form of energy. An important property of heat is that it flows from a body at higher temperature to another body at lower temperature.

When a tyre bursts suddenly energy is not immediately transferred between the system and the surrounding. So the process is adiabatic. There sudden expansion of its air into the atmosphere is adiabatic and the tyre is cooled. In adiabatic process, heat neither enters the system nor leaves the system.

Albedo is a measure of reflectivity.
This clearly indicates that all black surfaces have the lowest albedo. Fresh snow reflects approximately 95 percent of the sun's rays so it has the highest albedo.

Strain is a non-dimensional quantity.

The dimension of Planck constant equals to that of angular momentum.

The recoiling of gun is an example of Law of Conservation of Linear Momentum. When gun fires a bullet, it experiences a force in forward direction (action) , as a result the gun exerts a backward force (reaction) on the shoulder.