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Right OPTION is (B) 12.5J

The best explanation: The kinetic ENERGY of the BLOCK will change into internal energy of the system.

Initial kinetic energy = 0.5*1*25 = 12.5J.

Therefore the internal energy change = 12.5J.

The correct option is (a) True

Easy explanation: Two bodies are said to be in THERMAL equilibrium if they don’t exchange heat ENERGY when they are in physical CONTACT. For this only their temperatures have to be the same. Pressure and VOLUME will depend upon OTHERS properties like mass.

Right CHOICE is (a) 2/3

Explanation: The coefficient of a refrigerator is defined as α = Q2/W,where Q2 is heat extracted from a COLD RESERVOIR and W is work done.

α = 20/30 = 2/3.

Correct OPTION is (a) Wrev > Wirr

Explanation: A process is irreversible due to dissipative forces or free EXPANSION or EXPLOSIVE chemical reactions and so on. This causes it to lose the amount of USEFUL work that can be done in an irreversible process. This is not the case for a reversible process. Hence, Wrev > Wirr.

Right option is (c) In equilibrium at every state

To explain: A quasi static process is one in which each stage is in equilibrium with its SURROUNDINGS. There may be a process which may be quasi static and also involve heat transfer with SURROUNDING and will THEREFORE be irreversible. A process may not involve friction and be a free expansion of GAS and therefore can’t be quasi static.

Correct choice is (b) HEAT is a path variable

Explanation: INTERNAL energy CORRESPONDS to the mechanical energy of molecules. It is a state variable as it doesn’t DEPEND on the path taken. While heat is the energy in transit, so it is a path variable. Internal energy is a thermodynamic variable and is therefore macroscopic as thermodynamics deals with bulk SYSTEMS.

The correct option is (a) Conservation of ENERGY

To elaborate: The first law of THERMODYNAMICS is based on the conservation of energy. It DEALS with work done and heat energy supplied or removed from a SYSTEM. It basically says that energy supplied to a system is CONSERVED.

Correct answer is (C) 894K

The BEST I can EXPLAIN: For a carnot CYCLE: Q2/Q2 = T2/T1.

T2 = 12/4 * 298 = 894K.

The correct choice is (a) Isothermal expansion, adiabatic expansion, isothermal compression, adiabatic compression

Explanation: A carnot cycle is a reversible cyclic process having the maximum POSSIBLE EFFICIENCY. The STEPS of the cycle are: isothermal expansion of gas, adiabatic expansion, isothermal compression and then adiabatic compression. This is evident from its PV diagram:

Right answer is (c) Q2/W

To explain I would say: COEFFICIENT of performance of a refrigerator is DEFINED as the RATIO of heat EXTRACTED from the cold reservoir to the work DONE on the refrigerator.It is denoted by α = Q2/W.

The correct option is (b) 900J

For EXPLANATION: The EFFICIENCY of a carnot ENGINE is:

1- T2/T1 = 1-150/200 = 1/4.

Efficiency is also given by: 1 – Q2/Q1 = 1 – Q2/1200 = 1/4.

Q2 = 3/4 *1200 = 900J.

The correct option is (a) Temperature

Easy explanation: Zeroth law of thermodynamics talks about thermal equilibrium or RELATES bodies having no heat flow. Temperature difference is what leads to heat flow. So, this law helped in MAKING temperature MEASURABLE and an UNIVERSAL property of MATTER.

Right answer is (a) Expansion of gas, absorption of HEAT, heating of vapour, release of heat

Best explanation: In a REFRIGERATOR, the WORKING substance(gas) first gets expanded from high to LOW pressure which cools it into a vapour-liquid mixture. Then heat is absorbed from the region to be COOLED. Then the external work done on the system heats up the vapour. Finally, the vapour’s heat is released to the surroundings.

Correct choice is (a) 295cal

To elaborate: The first LAW states that ΔU=ΔQ – ΔW

= 315 – 20

= 295cal.

Work is POSITIVE as it is done by the system. HEAT is positive as it is supplied to the system.

The correct answer is (d) Translational, Vibrational & Rotational

Best explanation: Internal energy CONSISTS of the total KINETIC energy of all MOLECULES, which means all TYPES, namely translational, rotational & vibrational kinetic energies contribute to internal energy.

Right option is (b) BOYLE’s law

To explain I would say: In an isothermal process, PV=const. This is the same as Boyle’s law. Charle’s law is given by: V/T=const. Gay-Lussac’s law is given by: P/T=const and 2nd law of thermodynamics states that in EVERY process total entropy of the UNIVERSE MUST increase.

Correct answer is (a) EXTENSIVE

Easy explanation: The PRODUCT contains ONE term which is extensive, or which depends on mass, so we can say that their product also depends on mass and is therefore extensive.

Correct answer is (a) Entropy of an isolated system can NEVER DECREASE over TIME

The explanation: The second LAW STATES that entropy of an isolated system can never decrease over time. There can be a system whose entropy decreases, but, at the same time in that process another system’s increase in entropy will more than compensate for that decrease.

Right answer is (d) Total heat – Total work

The best I can EXPLAIN: In a cyclic process, the starting POSITION is the same as the ENDING position. So, the change in all state variables is zero. So the NET change in internal energy is zero. ΔU = ΔQ – ΔW = 0.

The correct OPTION is (c) -3.3J

To explain I would say: Since the process is ISOTHERMAL the PRODUCT PV will be constant.

PAVA =PBVB.

∴ VB = 1*3/3 = 1m^3.

Work done in an isothermal process is given by:

NRT*ln(VB/VA)

= PAVAln(VB/VA)

= 3ln(1/3)

= -3.3J.

Correct ANSWER is (d) A BODY cannot have heat energy in a PARTICULAR state

Easiest explanation: Heat energy is the energy in transit. A SYSTEM’s state cannot be defined by heat energy, it is defined by internal energy. Heat and WORK are path functions. Heat can be supplied or removed from a system but can’t define a system in a state.

Correct option is (c) DECREASE by an amount Q + P(V2 – V1)

Easiest explanation: The internal ENERGY will definitely decrease as both factors heat removal and work done by gas support the same. ΔU = ΔQ – ΔW = -Q – P(V2 – V1) = -(Q + P(V2 – V1)). THUS, we can say that internal energy DECREASES by an amount = Q + P(V2 – V1).

Right answer is (b) False

The explanation: The maximum POSSIBLE efficiency is GIVEN by:

1 – Tcold/Thot = 1 – 300/500 = 0.4.

The company claims that their ENGINE has an efficiency of (200-110)/200 = 0.45.

This is not possible as maximum efficiency is 0.4.

The correct ANSWER is (a) 2/5

Explanation: EFFICIENCY is DEFINED as work done/heat input.

Work done = 5-3=2J.

Heat input = 5J.

Thus, efficiency = 2/5.

The correct option is (d) Frictionless to and FRO motion

For explanation I would say: In frictionless to and fro motion, no form of energy is lost so the PATH followed from one point to another can be exactly RETRACED. While the other three are chemical CHANGES and cannot be reversed.

Right option is (a) True

Explanation: In the above said process, energy is conserved and ACCORDING to FIRST law, this is VALID. It only violates the second law. So, the GIVEN statement is true.

The correct answer is (a) True

Explanation: For an ideal gas INTERNAL energy depends only on temperature. In an ISOTHERMAL process CHANGE in temperature is zero, hence internal energy ALSO remains the same.

Correct option is (b) False

Best explanation: PATH variables like WORK and HEAT can only tell us the difference between state variables of two states. For describing a particular state of a thermodynamic system we need state variables like pressure, temperature and volume.

The correct OPTION is (b) The sum of kinetic and POTENTIAL energies of all molecules of the system

Explanation: The internal ENERGY of a system corresponds to the energy POSSESSED by all molecules. Thus it is the sum of kinetic and potential energies of all molecules in the system considered. Also note that potential energy is frame dependent, so we choose a frame in which the centre of mass is at rest.

The correct option is (a) 0.05J

To ELABORATE: When calculating internal ENERGY of molecules, the system is to be studied from a FRAME in which the centre of mass is at rest.So the kinetic energy due to movement of the ENTIRE box will not be CONSIDERED.Only the individual kinetic energies of molecules will be considered, and their value is:10^5*0.5*10^-6

= 0.05J.

Correct CHOICE is (a) 50J

Easy explanation: All the heat supplied will be equal to change in internal energy.

The WORK DONE is zero because the container is rigid hence no VOLUME change.

Thus, ΔU = ΔQ – ΔW = 50 + 0 = 50J.

Right answer is (b) False

For EXPLANATION I would say: Efficiency by DEFINITION can NEVER be greater than 1.Else the law of energy conservation will be VIOLATED.

Correct option is (b) False

To EXPLAIN I would say: A cyclic process is one in which the initial and final state is the same. The path need not be retraceable as in the case of a reversible process. For eg: a process COULD GO from A to B And then BACK to A, but via a DIFFERENT path.

Right answer is (B) 0.042J

The best I can explain: When the disc comes to REST all its kinetic energy will have been CONVERTED into INTERNAL energy of the system.

The fluid has a heat capacity of 2000J/K which MEANS that for 24J the change in temperature will be 24/2000 = 0.012K.

Given: ΔU = 3.5ΔT

⇒ ΔU = 3.5*0.012

= 0.042J.

Correct OPTION is (B) False

For explanation I would say: Equation of state is a RELATION between state variables.Only in the case of ideal GASES it is PV=nRT.So, there is a difference between the ideal gas equation and the equation of state in general.

The CORRECT ANSWER is (a) True

Explanation: Internal energy is a function of temperature only. So if ΔU=0 implies that the process will have CONSTANT temperature, or it is ISOTHERMIC.