Physics - Study Mode

[#736] Ampere second could be the unit of
Correct Answer

(D) Charge

Explanation

Solution: Ampere second could be the unit of charge.

[#737] Which one of the following is a good electrical conductor?
Correct Answer

(A) Graphite

Explanation

Solution: Conductivity is the capacity to transmit current or heat. Pure elemental silver is the best conductor of electricity. Copper, gold, aluminium are good conductors of electricity.

[#738] In a refrigerator, the cooling system should always be
Correct Answer

(B) At the bottom

Explanation

Solution: 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.

[#739] In a refrigerator what produces the cooling ?
Correct Answer

(D) None of these

Explanation

Solution: 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.

[#740] Which of the following has the highest entropy?
Correct Answer

(A) Hydrogen

Explanation

Solution: Hydrogen being gaseous has highest entropy.