Answer to Question #155137 in Electric Circuits for hamza

Question

i ) Describe any 4 natural/ industrial processes of adiabatic compression and

adiabatic expansion.

ii ) State how entropy changes are linked with Air pollution in modern world.

iii ) Describe the difference between capacitor and a capacitance. Also state the basic relation between frequency and capacitance.

Expert's answer

Answer 1

Explanations

1) Adiabatic process is a one in which no mass or energy crosses the boundryline of the described system. Those should be quicker processes in order to achieve such conditions.

Adiabtic compression

• The compression stoke of an engine
• Water condensation occurred during a sonic boom
• Cloud formation
• Fog formation

Adiabatic expansion

• Release of gas from a pressure vessel: cooler sensation to the touch
• Adiabatic wheel heat exchanger.

2)

• Air is said t be polluted when the unwanted particles exceed the allowed limit. So the main way of air pollution is release of gasses.
• From combustion, diffusion, vaporization etc the foreign substances enter the air to pollute it. (Naturally there is a balance in the environment so nothing exceed the limits & appears as pollutants)
• Combustion of coal: Coal is well packed/orderly arranged (by the environment itself) substance in which the entropy is less. When it is burnt it breaks in to heat energy, gas, soot etc where the entropy is higher.
• Now if we consider the reverse process: turn those gasses, soot & heat energy back into coal, it becomes a process of higher entropy to lower entropy which is very difficult & unusual & contradictory to the way of nature.
• But we have already done the easy part as burning coal & releasing the unwanted substances to the environment (lower entropy to higher entropy: natural tendency) which are of higher entropy which could become a pollutant when limits are exceeded.

• This is the usual entropy change for all the air pollutants.

3)

• The capacitor is the device used to store the electric charges while the capacitance is the quality of a particular substance to store electric charges in it. It is calculated by the ratio of the number of electric charges stored on the substance to the potential difference it is subjected to
• .As the frequency increases capacitance tend to decrease. This could be thought as, as the frequency increases rate of fluctuation of current increases, decreasing the amount of any particular charge that may come & stay inside the substance.