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Thermal Properties of Matter – Class 11 Physics notes, important questions and MCQs

NCERT Class 11 Physics, chapter 10. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Heat is energy transferred due to temperature difference. Bodies expand on heating, need specific heat and latent heat to change temperature or state, and transfer heat by conduction, convection and radiation.

Expansion and calorimetry

Linear expansion ΔL = αLΔT; β = 2α, γ = 3α (area and volume).
Q = mcΔT; latent heat Q = mL (water: L_fusion ≈ 334 kJ/kg, L_vap ≈ 2256 kJ/kg).
Water expands anomalously between 0 °C and 4 °C (densest at 4 °C).

Heat transfer

Conduction: H = KA(T₁ − T₂)/L.
Stefan–Boltzmann: E = σT⁴ (black body); Wien's law λₘT = constant.
Newton's law of cooling: rate of cooling ∝ (T − T₀) for small differences.

Key terms

Specific heat capacity: heat needed to raise 1 kg by 1 K
Latent heat: heat absorbed or released during change of state at constant temperature
Thermal conductivity: K in H = KAΔT/L; the rate of heat flow through unit area per unit temperature gradient

Formulas

Q = mcΔT
H = KAΔT/L
λₘT = b

Important questions with answers

Why do metal pipes and rails have gaps between sections?2 marks

Metals expand on heating. Gaps allow for thermal expansion in hot weather so the pipes or rails do not bend or buckle.

Explain why a body appears black, white or coloured, and state Kirchhoff's law of radiation.3 marks

A body that absorbs all wavelengths looks black; one that reflects all looks white; one that reflects some wavelengths shows those colours. Kirchhoff's law: at a given temperature, the ratio of emissive power to absorptivity is the same for all bodies and equals the emissive power of a black body; good absorbers are good emitters.

100 g of ice at 0 °C is added to 400 g of water at 40 °C. Find the final temperature (L = 336 J/g, c_water = 4.2 J/g °C).5 marks

Heat to melt ice = 100 × 336 = 33,600 J. Heat available from water cooling to 0 °C = 400 × 4.2 × 40 = 67,200 J, which is more, so all ice melts. Let final temperature be T: 400 × 4.2 × (40 − T) = 33,600 + 100 × 4.2 × T. 67,200 − 1680T = 33,600 + 420T, so 2100T = 33,600 and T = 16 °C.

Quick revision

Water is densest at 4 °C.
Hotter bodies emit at shorter peak wavelength.
Radiation needs no medium.

Exam tips

°F = (9/5)°C + 32; K = °C + 273.15.
In calorimetry, write heat lost = heat gained and include latent heat terms whenever a change of state occurs.

Practice MCQs

SI unit of specific heat capacity is
1. J/kg
2. W/m
3. J/K
4. J/(kg K)
Show answer
Answer: (d) J/(kg K). Per kg per K.
Water has maximum density at
1. 0 °C
2. −4 °C
3. 100 °C
4. 4 °C
Show answer
Answer: (d) 4 °C. Anomalous expansion.
100 °C in Fahrenheit is
1. 180 °F
2. 373 °F
3. 212 °F
4. 100 °F
Show answer
Answer: (c) 212 °F. 180 + 32.
Heat needed to raise 2 kg of water by 10 °C (c = 4200 J/kg K) is
1. 42,000 J
2. 21,000 J
3. 8,400 J
4. 84,000 J
Show answer
Answer: (d) 84,000 J. 2 × 4200 × 10.
1 kg of ice at 0 °C needs how much heat to melt (L = 336 kJ/kg)
1. 33.6 kJ
2. 4200 J
3. 3.36 kJ
4. 336 kJ
Show answer
Answer: (d) 336 kJ. Q = mL.
If the absolute temperature of a black body doubles, emitted power becomes
1. 2 times
2. 4 times
3. 8 times
4. 16 times
Show answer
Answer: (d) 16 times. E ∝ T⁴.
For a solid, volume expansion coefficient γ equals
1. α
2. 2α
3. 3α
4. α/3
Show answer
Answer: (c) 3α. γ = 3α.
A body cools from 80 °C to 60 °C in 5 minutes in a room at 20 °C. Using Newton's law (average form), the time to cool from 60 °C to 40 °C is about
1. 5 min
2. 6.5 min
3. 8.3 min
4. 15 min
Show answer
Answer: (c) 8.3 min. Rate ∝ excess: 4 °C/min at 50 °C excess, so 20/(0.08 × 30) ≈ 8.3 min.

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Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.