Is Thermodynamics part of the EAPCET Physics syllabus?

Yes. Thermodynamics is taught in Intermediate first year Physics, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.

How many Physics questions are there in EAPCET?

40 of the 160 questions in the Engineering paper are Physics, spread across 30 chapters.

What mistakes do students make in Thermodynamics?

Substituting Celsius temperatures into the Carnot efficiency or coefficient of performance — always convert to kelvin. Confusing adiabatic with isothermal — in an adiabatic process Q = 0 but the temperature changes; in an isothermal process ΔU = 0 but heat flows. Mixing up the sign of work — with ΔQ = ΔU + ΔW, work done by the gas (expansion) is positive and work done on the gas is negative. Using the engine efficiency formula for a refrigerator — its coefficient of performance is T₂/(T₁ − T₂), which can be greater than 1.

EAPCET Physics · Intermediate first year

Thermodynamics

Thermodynamics in Physics covers heat, work and internal energy, the first and second laws, thermodynamic processes and heat engines.

Subject: Physics
Taught in: Intermediate first year
Physics in the paper: 40 of 160 questions

Key formulas and results

First law: $\Delta Q = \Delta U + \Delta W$
Isothermal: $\Delta U = 0$ and $W = nRT\ln(V_{2}/V_{1})$
Adiabatic: $PV^{\gamma} =$ constant and $W = \frac{P_{1}V_{1} - P_{2}V_{2}}{\gamma - 1}$
Mayer’s relation: $C_{p} - C_{v} = R$
Carnot efficiency $\eta = 1 - \frac{T_{2}}{T_{1}}$
Refrigerator coefficient of performance $\beta = \frac{T_{2}}{T_{1} - T_{2}}$
Polytropic process $PV^{x} =$ constant: $W = \frac{nR\,\Delta T}{1 - x}$ and molar heat capacity $C = C_{v} + \frac{R}{1 - x}$ ; $x = 0$ isobaric, $1$ isothermal, $\gamma$ adiabatic, $\infty$ isochoric
$C_{v} = \frac{R}{\gamma - 1} = \frac{fR}{2}$ and $C_{p} = \frac{\gamma R}{\gamma - 1} = \frac{fR}{2} + R$
$\gamma$ in terms of degrees of freedom: $\gamma = 1 + \frac{2}{f}$
Isobaric process: $W = P\,\Delta V = nR\,\Delta T$ , $Q = nC_{p}\Delta T$ , $\Delta U = nC_{v}\Delta T$
Other adiabatic relations: $TV^{\gamma - 1} =$ constant and $P^{1 - \gamma}T^{\gamma} =$ constant; $W = -\Delta U = \frac{nR(T_{1} - T_{2})}{\gamma - 1}$
Mixture of gases: $C_{v,\text{mix}} = \frac{n_{1}C_{v1} + n_{2}C_{v2}}{n_{1} + n_{2}}$ and $\frac{n_{1} + n_{2}}{\gamma_{\text{mix}} - 1} = \frac{n_{1}}{\gamma_{1} - 1} + \frac{n_{2}}{\gamma_{2} - 1}$
Heat engine efficiency $\eta = \frac{W}{Q_{1}} = 1 - \frac{Q_{2}}{Q_{1}}$ ; refrigerator $\text{COP} = \frac{Q_{2}}{W} = \frac{Q_{2}}{Q_{1} - Q_{2}}$
Internal energy of $n$ moles of ideal gas: $U = \frac{f}{2}nRT$ , so $\Delta U = nC_{v}\Delta T$ for every process

What this chapter covers

Zeroth and first laws
Isothermal, adiabatic, isobaric and isochoric processes
Specific heats of gases
Second law
Heat engines and refrigerators
Carnot engine

How it is usually asked

Work done in a process
Efficiency of a heat engine
Reading PV diagrams
First-law calculations

Understanding Thermodynamics

Thermodynamics tracks energy flow between a system and its surroundings. The zeroth law defines temperature through thermal equilibrium. The first law is energy conservation: heat supplied to a gas goes partly into raising its internal energy and partly into work done by the gas as it expands. For an ideal gas, internal energy depends only on temperature, so ΔU = nCᵥΔT in any process.

Each standard process fixes one quantity. Isothermal processes keep T constant, so ΔU = 0 and Q = W. Adiabatic processes exchange no heat, so the work comes from internal energy. Isochoric processes do no work, and isobaric work is PΔV. On a PV diagram, work is the area under the curve.

The second law says no engine working in a cycle can convert all the heat it absorbs into work; some heat must be rejected to a colder sink. A Carnot engine working between absolute temperatures T₁ and T₂ has the maximum possible efficiency, 1 − T₂/T₁, and no real engine between the same temperatures can beat it. EAPCET often tests efficiencies, work from PV diagrams and first-law bookkeeping.

Worked example

EAPCET-style question

A Carnot engine works between a source at 527 °C and a sink at 127 °C. Its efficiency is

(1)50%
(2)75.9%
(3)25%
(4)66.7%

Solution

Convert to kelvin: $T_{1} = 527 + 273 = 800\ \text{K}$ and $T_{2} = 127 + 273 = 400\ \text{K}$ .
$\eta = 1 - \frac{T_{2}}{T_{1}} = 1 - \frac{400}{800}$ .
$\eta = 0.5 = 50\%$ .
Using Celsius values directly would wrongly give about 75.9%.

Answer: 50%

Shortcuts and results to remember

At constant pressure the fraction of heat used for work is $R/C_{p}$ : $2/5$ for a monatomic gas and $2/7$ for a diatomic gas; the rest ( $3/5$ or $5/7$ ) raises internal energy.
Isothermal: $\Delta U = 0$ so $Q = W$ ; adiabatic: $Q = 0$ so $W = -\Delta U$ .
Sign convention: heat given to the system is positive and work done by the system is positive.
Bulk modulus of a gas is $P$ for an isothermal change and $\gamma P$ for an adiabatic change.
On a V–T graph, straight lines through the origin are isobars with slope $\propto 1/P$ , so the steeper line is at lower pressure; likewise on a P–T graph slope $\propto 1/V$ .

Common mistakes to avoid

Substituting Celsius temperatures into the Carnot efficiency or coefficient of performance — always convert to kelvin.
Confusing adiabatic with isothermal — in an adiabatic process Q = 0 but the temperature changes; in an isothermal process ΔU = 0 but heat flows.
Mixing up the sign of work — with ΔQ = ΔU + ΔW, work done by the gas (expansion) is positive and work done on the gas is negative.
Using the engine efficiency formula for a refrigerator — its coefficient of performance is T₂/(T₁ − T₂), which can be greater than 1.

How to prepare it

Work done equals the area under the PV curve; for a cycle, it is the enclosed area.

Once the formulas feel familiar, test them the way the exam does: practise Thermodynamics questions chapter-wise, then attempt a full previous year paper to see whether it holds up under a 3-hour timer.

Related Physics chapters

See every chapter in the EAPCET Physics syllabus.

Practise Thermodynamics chapter-wise

Chapter-wise quizzes show exactly which topics in this chapter you still get wrong — before a full paper does.

Frequently asked questions

Is Thermodynamics part of the EAPCET Physics syllabus?: Yes. Thermodynamics is taught in Intermediate first year Physics, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.
How should I prepare Thermodynamics for EAPCET?: Work done equals the area under the PV curve; for a cycle, it is the enclosed area.
How many Physics questions are there in EAPCET?: 40 of the 160 questions in the Engineering paper are Physics, spread across 30 chapters.
What mistakes do students make in Thermodynamics?: Substituting Celsius temperatures into the Carnot efficiency or coefficient of performance — always convert to kelvin. Confusing adiabatic with isothermal — in an adiabatic process Q = 0 but the temperature changes; in an isothermal process ΔU = 0 but heat flows. Mixing up the sign of work — with ΔQ = ΔU + ΔW, work done by the gas (expansion) is positive and work done on the gas is negative. Using the engine efficiency formula for a refrigerator — its coefficient of performance is T₂/(T₁ − T₂), which can be greater than 1.