Class 11 Physics Thermodynamics – Complete Chapter Guide with PYQs

Thermodynamics Class 11 Physics ka woh chapter hai jahan bahut se students ka confidence hilta hai — heat, work, internal energy, aur teen-chaar tarah ke processes, sab ek saath. Lekin ek baar first law samajh mein aa gaya, toh poora chapter ek hi thread pe khada dikhta hai. Aur accha news yeh hai: yeh chapter Class 11 board mein toh aata hi hai, JEE aur NEET dono mein bhi confirm questions deta hai.

Iss guide mein hum poora chapter simple bhaasha mein khol rahe hain — first law se lekar Carnot engine tak — Burari aur Sant Nagar ke students ke liye, taaki rate rate ke nahi, samajh ke marks aayein.

Basic Terms Aur Zeroth Law

System woh hai jise hum study karte hain, surroundings baaki sab. Thermodynamic variables — pressure (P), volume (V), temperature (T). Zeroth law: agar do systems ek teesre ke saath thermal equilibrium mein hain, toh woh aapas mein bhi equilibrium mein honge — isi se temperature ki definition aati hai.

First Law Of Thermodynamics

Yeh poore chapter ki neenv hai — bas energy conservation:

ΔQ = ΔU + ΔW

• ΔQ = system ko di gayi heat
• ΔU = internal energy mein change (sirf temperature pe depend, ideal gas)
• ΔW = system dwara kiya gaya work = P·ΔV

Sign convention dhyaan se — heat andar aane pe +, system work kare toh +. Yahi jagah students sabse zyada marks khote hain.

Thermodynamic Processes

• Isothermal: T constant → ΔU = 0 → ΔQ = ΔW. PV = constant.
• Adiabatic: Q = 0 → ΔW = −ΔU. PV^γ = constant.
• Isobaric: P constant → ΔW = PΔV.
• Isochoric: V constant → ΔW = 0 → ΔQ = ΔU.

Har process ka P-V diagram banana aana chahiye — board mein aksar 'graph ke area = work' wale questions aate hain.

Cp, Cv Aur Mayer's Relation

Gas ki do specific heats hoti hain — constant pressure pe (C_p) aur constant volume pe (C_v). Inka relation:

• C_p − C_v = R  (Mayer's relation)
• γ = C_p/C_v  (monatomic 1.67, diatomic 1.4)

Second Law, Heat Engines Aur Carnot

First law energy ka hisaab rakhta hai, but second law batata hai ki heat apne aap thande se garam ki taraf nahi jaati, aur koi engine 100% efficient nahi ho sakta.

• Heat engine efficiency: η = 1 − Q₂/Q₁
• Carnot (maximum) efficiency: η = 1 − T₂/T₁  (T in Kelvin)
• Refrigerator: coefficient of performance β = Q₂/(Q₁ − Q₂)

Carnot efficiency wala numerical almost pakka aata hai — sirf yaad rakhna ki temperature Kelvin mein daalni hai, Celsius mein nahi.

Common Mistakes

• Sign convention galat — heat in +, work by system +. Pehle decide karo, phir consistent raho.
• Isothermal mein ΔU ko non-zero maanna — T constant hai toh ΔU = 0.
• Carnot mein Celsius use karna — hamesha Kelvin (K = °C + 273).
• P-V diagram na banana — work = area, diagram ke bina galti hoti hai.

Frequently Asked Questions