Engines and cycles - class-XI

The correct answer is option(A).

There are two dead centers in one cycle of the steam engine:

• Top dead center
• Bottom dead center

Amount of heat goes in the engine        $Q _H = 3000$ J

Amount of heat absorbed       $Q _H = 60$ J

Efficiency of heat engine= $\frac{work done}{heat input}$ Going by the above options efficiency is maximum in option D, and is equal to 40 percent.

Efficiency of engine   $\eta = \dfrac{W}{Q _H}$  

Efficiency is defined as work done per unit of heat consumed . It doesn't depend on the substance on which we work.

The efficiency of a heat engine is defined as the ratio of work output to the heat input.
Thus, $ \eta = \dfrac{W}{{Q} _{in}} $
Now, since the heat energy only gets converted into work and no other form of energy, thus following the law of conservation of energy,
$ W = {Q} _{out} - {Q} _{in} $
Substituting this value in the above expression, we get another expression for the efficiency of a heat engine

The efficiency of heat engine will be$:$

The efficiency of heat engine is $\eta=\dfrac{W}{Q _{in}}$  

Temperature of source     $T _H = 750^oC = 750+273 = 1023$  K

Let, $E _D,E _P,E _S$ denote efficiency of a diesel, a petrol stream engine respective.

Efficiency of heat engine,

The electric engine is most efficient. Electric motors are very efficient at converting electricity into work. Physicists throw around abstract numbers like 90%, whereas when discussing combustion engines, they use numbers less than 40%. But you cannot compare the efficiency of converting electricity into motion to the efficiency of converting gasoline into motion.

We know that in heat engine, sink is at lower temperature than source, hence,

Let us consider $T _1=$ temperature of the source

A refrigerator is infact a reverse heat engine which absorbs heat from source (material) at lower temperature, do work on it and then passes the heat to the sink (sorrounding) at higher temperature, thus we can say that heat is removed from inside the refrigerator.

When the door of a refrigerator is opened the temperature of the room increases as the room is acting as the source here where the heat is rejected.

A refrigerator is a heat engine which works in the reverse manner, to cool the substance inside.

A condenser is simply a heat exchanger,the purpose of a condenser in the cycle of compression refrigeration is to change the hot gas being discharged from the compressor to a liquid prepared for use in the evaporator. The condenser accomplishes this action by the removal of sufficient heat from the hot gas, to ensure its condensation at the pressure available in the condenser. The heat is shifted to another medium, like water or air, to cool the condenser.

Though the working principle of refrigerator and heat pump is same but heat pump is used to warm a room whereas refrigerator is used to cool down the temperature of material inside it , so heat pump is also called a reverse refrigerator .

A heat pump is a device that transfers heat energy from a source of heat to what is called a "heat sink". Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses a small amount of external power to accomplish the work of transferring energy from the heat source to the heat sink. A condenser is a device or unit used to condense a substance from its gaseous to its liquid state, by cooling it.

A heat pump is a device that transfers heat energy from a source of heat to what is called a "heat sink". Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses a small amount of external power to accomplish the work of transferring energy from the heat source to the heat sink,there are four main components of heat pump: compressor, condenser, expansion valve and evaporator

A refrigerant is generally a fluid , which undergoes state change , from liquid to gas and back again . Chlorofluorohydrocarbons are most commonly used  as refrigerant in heat pumps . 

The coefficient of performance (COP) for a Carnot refrigerator is T_cold / (T_hot - T_cold). With T_cold = 300K and T_hot = 373K, COP = 300 / 73 = 4.11. Heat removed from cold source (Q_cold) = COP * Work. Heat added to hot source (Q_hot) = Q_cold + Work = Work * (COP + 1). To convert 1 kg of water to vapor requires 2260 kJ. Using the ratio of heat transfer, the mass of ice frozen is calculated based on the latent heat of fusion (334 kJ/kg).

A refrigerant is a substance or mixture, usually a fluid, used in a heat pump and refrigeration cycle. In most cycles it undergoes phase transitions from a liquid to a gas and back again.A heat pump is a device that transfers heat energy from a source of heat to what is called a "heat sink". Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses a small amount of external power to accomplish the work of transferring energy from the heat source to the heat sink.

$\therefore Heat\quad absorption=\dfrac { { T } _{ 1 }-{ T } _{ 2 } }{ { T } _{ 1 } } $

${ T } _{ 1 }=1600K$