A reaction is spontaneous when. A refrigeration system. The third law of thermodynamics:. If dQ is the heat given to thermodynamic system and dU is its change in internal energy and dW is the work done by the system, then the first law of thermodynamics concludes that:.
Suggested Test Series. Suggested Exams. More Physics Questions Q1. X-rays were discovered by:. When a body is immersed in a liquid the upward force experienced by it is known as :. Which among the following is a non-conservative force? The work done to move a unit charge from a point to another is called :. On which of the following scientific principles is an electric generator based? Which among the following is used in making windows for the X-ray tubes? How many electrons taken together make one coulomb?
An electron possesses a negative charge of:. The term radioactivity was coined by:. All for free. Explore Testbook Learn to attain the subject expertise with us. Concept: The zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other. The first law of thermodynamics states that energy cannot be created or destroyed in an isolated system; energy can only be transferred or changed from one form to another.
The first law of thermodynamics is a restatement of the law of conservation of energy i. Hence option 2 is correct among all Tricks to remember: This is the conclusive point for all three laws of thermodynamics. Isobaric Isochoric Adiabatic Isothermal. The thermodynamic process in a system, during which no heat transfer occurs between thermodynamic systems and surrounding is called an adiabatic process. So option 3 is correct. Get Started for Free Download App.
Increases Degreases Remains Constant First increases and then becomes constant. It gives the maximum possible efficiency among all types of heat engines. The part of the Carnot engine which provides heat to the engine is called a heat source. The temperature of the source is maximum among all the parts. The part of the Carnot engine in which an extra amount of heat is rejected by the engine is called as a heat sink.
The amount of work which is done by the engine is called as work done. If the temperature of the source T H is increased then the efficiency of the Carnot engine increases. So option 1 is correct. Answer Detailed Solution Below Option 4 : 1. Carnot engine operates through a series of two isothermal and adiabatic processes called the Carnot cycle.
The steps of the Carnot cycle are Isothermal expansion Adiabatic expansion Isothermal compression Adiabatic compression The efficiency of the Carnot engine is defined as the ratio of network done per cycle by the engine to heat absorbed per cycle by the working substance from the source. The steps of the Carnot cycle are Isothermal expansion Adiabatic expansion Isothermal compression Adiabatic compression The efficiency of the Carnot engine is defined as the ratio of net work done per cycle by the engine to heat absorbed per cycle by the working substance from the source.
It gives the estimate of the maximum possible efficiency that a heat engine during the conversion process of heat into work and conversely, working between two reservoirs, can possess. So practically and theoretically there can not be any engine with more efficiency than Carnot engine. The efficiency of this type of engine is independent of the nature of the working substance and is only dependent on the temperature of the hot and cold reservoirs.
Answer Detailed Solution Below Option 2 : do external work. As we know that, the internal energy of the system is a function of temperature alone , so in the isothermal process, the change in internal energy is zero. Hence option 2 is correct. Concept : The first law of thermodynamics is a restatement of the law of conservation of energy. It states that energy cannot be created or destroyed in an isolated system; energy can only be transferred or changed from one form to another.
When heat energy is supplied to a thermodynamic system or any machine. Two things may occur: The internal energy of the System or machine may change. The system may do some external work. CONCEPT : Zeroth law of thermodynamics: If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.
The first law of thermodynamics: Energy can neither be created nor destroyed. The change in the temperature of the environment is usually negligible compared with the change in the temperature of the system. Thus, the net transfer of energy takes place only when there is temperature difference. Change in Internal Energy of a System :. Consider a system S consisting of some quantity of gas enclosed in a cylinder fitted with a movable, massless, and frictionless piston see below fig. Suppose the gas is heated using a burner source of heat, environment.
The other way to increase the internal energy of the gas is to quickly push the piston inside the cylinder, so that the gas is compressed, as shown in below Fig. In this case, we know that the piston does some work on the system gas in moving it through some distance. The system gains energy and its temperature is increased. On the other hand, if the system gas pushes the piston out, so that the gas is expanded, some work is done by the system gas. It loses some of its energy and the system gas cools down.
Why is there a change in the energy of a gas when its volume changes? When we compress a gas, we increase the momentum of gas molecules, thereby increasing the energy of the gas.
On the contrary, in the expansion of a gas, there is decrease in the momentum of gas molecules resulting in decrease in the energy of the gas. First law of thermodynamics. First law of thermodynamics : The change in the internal energy of a system DU is the difference between the heat supplied to the system Q and the work done by the system on its surroundings W. See fig. During expansion of the gas, molecules colliding with the piston lose momentum to it.
This exerts force and hence pressure on the piston, moving it outward through a finite distance. Here, the gas does a positive work on the piston. There is increase in the volume of the gas. The work done by the piston on the gas is negative.
During compression of the gas, molecules colliding with the piston gain momentum from it. The piston moving inward through a finite distance exerts force on the gas. Here, the gas does a negative work on the piston. There is decrease in the volume of the gas. The work done by the piston on the gas is positive. Expression for the work done by a gas :. See Fig. Let the cross sectional area of the cylinder and the piston be A , and the constant pressure exerted by the system on the piston be p.
If the piston moves through an infinitesimal very small distance dx , the work done by this force is,. Hence, the work done by the system in bringing out this infinitesimal change in the volume can be written as,. If the initial volume of the cylinder is V i and its volume after some finite change is V f , then the total work done in changing the volume of the cylinder is,.
The change in volume in this case is small. Positive work with varying pressure :. Suppose the gas is allowed to expand by moving the piston outward extremely slowly. There is decrease in pressure of the gas as the volume of the gas increases.
Figure shows the corresponding p— V diagram. In this case, the work done by the gas on its surroundings,. Negative work with varying pressure :. Let us now suppose that starting from the same initial condition, the piston is moved inward extremely slowly so that the gas is compressed. There is increase in pressure of the gas as the volume of the gas decreases. Below figure shows the corresponding p—V diagram. Positive work at constant pressure :. In this case, during the expansion, the work done by the gas,.
Verify that the area under the P— V curve has dimensions of work. Area under the P— V curve is , where P is the pressure and V is the volume. Thermodynamics state variables. Property of a system or a system variable : The property of a system or a system variable is any measurable or observable characteristic or property of the system when the system remains in equilibrium.
Macroscopic variables of a system : Pressure, volume, temperature, density, mass, specific volume, amount of substance expressed in mole are macroscopic variables of a system.
Intensive variable : A variable that does not depend on the size of the system is called an intensive variable. Examples : pressure, temperature, density.
Extensive variable : A variable that depends on the size of the system is called an extensive variable. Examples : internal energy, mass. Mechanical equilibrium : A system is said to be in mechanical equilibrium when there are no unbalanced forces within the system and between the system and its surroundings. A system is said to be in mechanical equilibrium when the pressure in the system is the same throughout and does not change with time.
Note : The constituents of a system, atoms, molecules, ions, etc. Chemical equilibrium : A system is said to be in chemical equilibrium when there are no chemical reactions going on within the system. A system is said to be in chemical equilibrium when its chemical composition is the same throughout the system and does not change with time. Note : In this case, in the absence of concentration gradient, there is no diffusion, i. Thermal equilibrium : A system is said to be in thermal equilibrium when its temperature is uniform throughout the system and does not change with time.
Eventually, the air in first case, and the fuel in the second case reach a uniform temperature and pressure and attain thermal and mechanical equilibrium with its surroundings. Thus it attains thermodynamic equilibrium. Equation of state : The mathematical relation between the state variables pressure, volume, temperature, amount of the substance is called the equation of state.
For a fixed mass of gas, the number of moles, n, is constant. R is the universal gas constant. Thus, out of pressure P , volume V and thermodynamic temperature T , only two any two are independent.
Thermodynamics process. Thermodynamic process : A procedure by which the initial state of a system changes to its final state is called a thermodynamic process. During the process, there may be. Quasistatic process : A quasistatic process is an idealised process which occurs infinitely slowly such that at all times the system is infinitesimally close to a state of thermodynamic equilibrium.
Work Done During a Thermodynamic Process:. Let us understand the relation between a path and the work done along a path. The work done by the gas W is the area under the curve and is different in each case. W depends on the path followed. Hence, it follows that heat transferred to the system Q depends on the path followed. Reversible process : A reversible process is one which is performed in such a way that, at the conclusion of the process, both the system and its local surroundings are restored to their initial states, without producing any change in the rest of the universe.
A process may take place reversibly if it is quasistatic and there are no dissipative effects. Such a process cannot be realized in practice. Irreversible process : A process which does not fulfill the rigorous requirements of reversibility is said to be an irreversible process.
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