SSC CGL Physics · Heat and Thermodynamics
Heat, Latent Heat and Thermodynamics
Why steam burns worse than boiling water, how an earthen pot cools water, the copper calorimeter, spit-roasting, the zeroth law, and heat engines.
Why this matters
Six questions in the bank, two from each year's shifts. Each turns on one idea, latent heat most often, so learn why each everyday case works.
Concept 1 of 2: Heat in daily life
Definition
The cases:
- Steam at 100 degrees burns worse than water at 100 degrees: as it condenses on skin it also gives up its latent heat of vaporisation (about 2,260 J per gram).
- An earthen pot (matka) is porous: water seeps out and evaporates from the outside, taking latent heat from the water inside. Water vapour does not come in.
- A calorimeter is a thin copper vessel: copper conducts well and takes little heat itself.
- Spit-roasting cooks food on a turning rod by the fire's radiant heat and hot air.
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 1 · Heat and Thermodynamics · Heat, Latent Heat and Thermodynamics
Steam is not hotter
Concept 2 of 2: Laws of thermodynamics and engines
Definition
The facts:
- Zeroth law: two bodies each in equilibrium with a third are in equilibrium with each other. Ralph H. Fowler named it (1930s).
- An ideal (Carnot) engine's efficiency = 1 minus Tcold / Thot: it depends only on the two temperatures.
- Heat flows from cold to hot only with work done (as in a refrigerator).
- A slow, reversible expansion gives the most work; an irreversible one gives less.
| Statement | True or false |
|---|---|
| Named the zeroth law | Ralph H. FowlerQ |
| Ideal efficiency depends only on temperatures | True |
| Irreversible expansion gives more work | False |
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 2 · Heat and Thermodynamics · Heat, Latent Heat and Thermodynamics
Maxwell stated it, Fowler named it
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (2)
Heat in daily life3 rows
Laws of thermodynamics and engines3 rows
| Statement | True or false |
|---|---|
| Named the zeroth law | Ralph H. FowlerQ |
| Ideal efficiency depends only on temperatures | True |
| Irreversible expansion gives more work | False |
Watch out for (2)
- Steam is not hotter→ Heat in daily life
- Maxwell stated it, Fowler named it→ Laws of thermodynamics and engines
Test yourself on a real paper
Sit a past SSC CGL paper, timed and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.