Physics
Thermodynamics Explained Without the Confusion
By Dr. Sandhya Classes Editorial Team · Published 2026-10-03 · Updated 2026-10-03 · 3 min read
Laws of thermodynamics, sign conventions and PV diagrams made easy for Class 11.
Physics at Dr. Sandhya Classes is taught personally by Dr. Sandhya, Ph.D. in Physics, teaching since 2015 — offline in Zirakpur (Highland Marg & Lohgarh Road) and online across India. About Dr. Sandhya
Fix your sign convention
Most confusion in Thermodynamics comes from sign conventions for heat and work. Choose the NCERT convention and use it consistently.
The first law as energy accounting
Heat supplied is shared between internal energy change and work done by the system.
Reading PV diagrams
Area under the curve represents work. Practise isothermal, adiabatic, isobaric and isochoric processes side by side.
The second law and engines
No engine converts all heat into work. Efficiency questions follow directly from this idea.
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