MHT-CET Physics · Teaching notes
Thermal Properties of Matter — MHT-CET Physics
Thermal Properties of Matter has 84 past-year questions in the MHT-CET bank, and nearly two thirds of them are about radiation. Stefan's law sets how fast a hot body radiates, Wien's law where its spectrum peaks, and Newton's law of cooling how quickly it reaches room temperature; together they carry 12 of the 14 HARD questions. The rest is thermal expansion, a little calorimetry, and conduction through a rod or a slab. Every PYQ is tagged.
Every subtopic, worked example, formula and trap in one printable document — answers shown, ready to share.
Subtopic notes
Temperature Scales and Thermal Expansion
19 PYQsA solid grows in every dimension when heated: its length by αLΔT, its area by 2αAΔT and its volume by 3αVΔT, where α is the coefficient of linear expansion; the Celsius, Fahrenheit and Kelvin scales are linear relabellings of one another.
Calorimetry: Heat Lost Equals Heat Gained
4 PYQsWhen hot and cold bodies share heat in isolation, the heat one loses equals the heat the other gains, Q = mcΔT for a temperature change and Q = mL for a change of state; a body's heat capacity mc is the heat that raises it by one degree.
Conduction Through Rods and Slabs
8 PYQsHeat flows along a rod at the rate Q/t = KAΔT/L, which is the temperature difference divided by the thermal resistance L/KA; slabs in series add their resistances and rods side by side add their conductances, exactly like electrical resistors.
Radiation: Stefan, Wien and Newton's Law of Cooling
53 PYQsA hot body radiates power P = eσAT⁴ (Stefan's law), its spectrum peaks at λ_m = b/T (Wien's law), and a body a little warmer than its surroundings cools at a rate proportional to its excess temperature (Newton's law of cooling); a black body absorbs everything and has e = 1.
Formula & revision sheet
8 formulas · 1 reference tables · 14 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
8 formulas · 1 reference tables · 14 gotchas across all subtopics — the exam-eve cheat-sheet
Formulas (3)
Watch out for (4)
- Forgetting the 32 in Fahrenheit→ Converting Between Temperature Scales
- Pairing the longer rod with the larger α→ Linear Expansion and Rods That Keep Their Difference
- Using the final length in ΔL = αLΔT→ Linear Expansion and Rods That Keep Their Difference
- Using α for a volume→ Area and Volume Expansion
Watch out for (2)
- Averaging temperatures when ice is present→ Mixing, Melting and Heat From Motion
- Confusing heat capacity with specific heat→ Mixing, Melting and Heat From Motion
Formulas (1)
Watch out for (2)
- Adding conductivities for slabs in series→ Rate of Flow and Thermal Resistance
- Scaling the flow with the area alone→ Rate of Flow and Thermal Resistance
Formulas (3)
Reference tables (1)
Absorbed, Reflected, Transmitted, and the Black Body5 rows
| Quantity | Rule |
|---|---|
| Incident heat | absorbed + reflected + transmitted |
| Opaque body | t = 0, a + r = 1 |
| Perfect black body | a = 1, emissivity e = 1 |
| Rate of cooling by colour | black > red > white |
| Area under the intensity–wavelength curve | total power per unit area, all wavelengths |
Watch out for (6)
- Leaving out the transmitted part→ Absorbed, Reflected, Transmitted, and the Black Body
- Using degrees Celsius in T⁴→ Stefan's Law: Power Grows as T⁴
- Ignoring the surroundings in a cooling rate→ Stefan's Law: Power Grows as T⁴
- Raising the wavelength ratio to the fourth power the wrong way→ Wien's Law: the Peak Moves With Temperature
- Forgetting the size when bodies differ→ Wien's Law: the Peak Moves With Temperature
- Using the starting temperature instead of the average→ Newton's Law of Cooling
PYQ weightage by concept
9 concepts · 84 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
9 concepts · 84 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Linear Expansion and Rods That Keep Their Difference | 11 | 13% |
| Area and Volume Expansion | 6 | 7% |
| Converting Between Temperature Scales | 2 | 2% |
| Concept | PYQs | Share |
|---|---|---|
| Mixing, Melting and Heat From Motion | 4 | 5% |
| Concept | PYQs | Share |
|---|---|---|
| Rate of Flow and Thermal Resistance | 8 | 10% |
| Concept | PYQs | Share |
|---|---|---|
| Stefan's Law: Power Grows as T⁴ | 22 | 26% |
| Wien's Law: the Peak Moves With Temperature | 11 | 13% |
| Absorbed, Reflected, Transmitted, and the Black Body | 10 | 12% |
| Newton's Law of Cooling | 10 | 12% |
Test yourself on Thermal Properties of Matter
20 past MHT-CET questions from this chapter, timed at 18 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.