Thermal Properties of Matter Notes for NEET and JEE Main 2027

Thermal Properties of Matter is Chapter 10 of NCERT Class 11 Physics (Part II) and part of Unit 7, Properties of Solids and Liquids, in both the NEET UG and JEE Main syllabus. These notes cover temperature scales, thermal expansion, specific heat, calorimetry, change of state, latent heat, conduction, convection, radiation and Newton’s law of cooling, with a PDF.

Thermal Properties of Matter Notes for NEET and JEE Main

Section-wise key points from NCERT Chapter 10, formula tables, high-yield facts and common mistakes for 2027 revision.

Thermal Properties of Matter at a Glance

The topic list follows the NEET UG 2026 syllabus released by the National Medical Commission (NMC) on 22 December 2025 and the JEE Main 2026 syllabus published by the National Testing Agency (NTA). Both stay the reference until the 2027 syllabi are out. The full lists are on the NEET syllabus and JEE Main syllabus pages.

Temperature and Heat

Heat is energy that flows between a body and its surroundings because of a temperature difference; temperature is the measure of a body’s hotness.

• Heat flows from the body at higher temperature to the one at lower temperature until both reach the same temperature (thermal equilibrium).
• SI unit of heat: joule (J). SI unit of temperature: kelvin (K); °C is also commonly used.
• Any energy transfer that does not involve a temperature difference is not heat.

Measurement of Temperature and Temperature Scales

A thermometer uses a thermometric property that changes with temperature, such as the expansion of mercury or alcohol in a glass tube.

• Conversion: t_F = (9/5)t_C + 32, or (t_F − 32)/180 = t_C/100.
• Kelvin and Celsius have the same unit size: T = t_C + 273.15.
• Liquid-in-glass thermometers using different liquids can disagree away from the fixed points; a constant-volume gas thermometer at low density gives the same reading whatever the gas.
• Absolute zero is −273.15 °C (0 K), the base of the Kelvin scale.
• The triple point of water, 273.16 K, is the preferred fixed point because it has a unique temperature.

Ideal-gas Equation and Absolute Temperature

Low-density gases obey PV = µRT, combining Boyle’s law (PV constant at fixed T) and Charles’ law (V/T constant at fixed P).

• µ is the number of moles and R = 8.31 J mol⁻¹ K⁻¹ is the universal gas constant.
• At constant volume, pressure varies linearly with temperature; extending the line to zero pressure gives −273.15 °C for every low-density gas.

Thermal Expansion

Most substances expand on heating; the fractional change in size per kelvin is the coefficient of expansion.

• Metals expand more than glass: copper expands about five times more than glass for the same temperature rise.
• Alcohol (ethanol) has a larger α_v than mercury.
• For an ideal gas at constant pressure, α_v = 1/T; at 0 °C it is 3.7 × 10⁻³ K⁻¹, much larger than for solids and liquids.
• Anomalous expansion of water: it contracts on heating from 0 °C to 4 °C and has maximum density at 4 °C. Lakes therefore freeze from the top, and life below survives.
• Thermal stress: if a rod’s ends are fixed, stress = Yα_lΔT. NCERT example: a steel rail heated by 10 °C develops 2.4 × 10⁷ N m⁻².

Specific Heat Capacity and Calorimetry

The heat needed to raise a body’s temperature depends on its mass, the temperature change and the nature of the substance.

• For gases, C_p (constant pressure) and C_v (constant volume) are defined separately.
• Water has the highest specific heat capacity among the substances in NCERT’s table (4186 J kg⁻¹ K⁻¹), so it is used as a coolant in car radiators and in hot water bags, and sea breezes have a cooling effect.
• Calorimetry: in an isolated system, heat lost by the hotter part equals heat gained by the colder part.
• A calorimeter is a metal vessel and stirrer of the same material (copper or aluminium) inside a wooden jacket packed with an insulator such as glass wool.

Change of State and Latent Heat

During a change of state, added heat changes the state, not the temperature: Q = mL.

• Steam at 100 °C carries 22.6 × 10⁵ J kg⁻¹ more heat than water at 100 °C, so steam burns are more serious.
• Regelation: ice melts under pressure and refreezes when the pressure is removed (a weighted wire passes through an ice slab); skating works because pressure forms water under the skates.
• Boiling point falls with lower pressure (cooking is hard on hills) and rises with higher pressure (a pressure cooker cooks faster). The boiling point at 1 atm is the normal boiling point.
• The triple point is where solid, liquid and vapour coexist; for water it is 273.16 K.
• L depends on pressure; values are usually quoted at standard atmospheric pressure.

Heat Transfer: Conduction, Convection and Radiation

Heat moves by three modes; conduction and convection need a medium, radiation does not.

Conduction

• Rate of heat flow through a bar: H = KA(T_C − T_D)/L, where K is the thermal conductivity (SI unit W m⁻¹ K⁻¹).
• Metals are good conductors (copper 385 W m⁻¹ K⁻¹); air is a poor conductor (0.024 W m⁻¹ K⁻¹).
• Two bars of equal length and area in series: junction temperature T₀ = (K₁T₁ + K₂T₂)/(K₁ + K₂) and equivalent conductivity K′ = 2K₁K₂/(K₁ + K₂).

Convection

• Natural convection depends on gravity and buoyancy; forced convection uses a pump, as in home heating, the human circulatory system and car engine cooling.
• By day the land heats faster than the sea, giving a sea breeze; at night the cycle reverses.
• Trade winds blow from the north-east towards the equator because of unequal solar heating modified by the earth’s rotation.

Radiation

• Black bodies absorb and emit radiation better than light-coloured bodies: white clothes in summer, dark clothes in winter, blackened bottoms of cooking pots.
• A thermos (Dewar) flask has double glass walls coated with silver, with vacuum between them to cut conduction and convection.

Blackbody Radiation: Wien’s and Stefan-Boltzmann Laws

Thermal radiation has a continuous spectrum, and its peak shifts to shorter wavelengths as temperature rises.

• Wien’s displacement law: λ_mT = constant = 2.9 × 10⁻³ m K.
• Heated iron glows dull red, then reddish yellow, then white hot.
• NCERT estimates: the moon (λ_m about 14 µm) at 200 K; the Sun’s surface (λ_m = 4753 Å) at 6060 K.
• Blackbody curves are universal: they depend only on temperature, not on the size, shape or material of the body.
• Stefan-Boltzmann law for a perfect radiator: H = AσT⁴, with σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴.
• For a body of emissivity e: H = AeσT⁴; net loss to surroundings at T_s: H = eσA(T⁴ − T_s⁴).
• e = 1 for a perfect radiator; lamp black comes close, and a tungsten lamp has e of about 0.4.

Newton’s Law of Cooling

The rate at which a body loses heat is proportional to the difference between its temperature and that of its surroundings, for small temperature differences.

• −dQ/dt = k(T₂ − T₁), where T₂ is the body’s temperature, T₁ the surroundings’ and k depends on the area and nature of the surface.
• With dQ = ms dT₂: dT₂/dt = −K(T₂ − T₁), K = k/ms, giving T₂ = T₁ + C′e^−Kt.
• The rate of cooling is highest at first and falls as the body approaches room temperature.
• It applies to a radiator warming a room, heat loss through a wall, or a cup of tea cooling on a table.

Most-asked Facts for NEET and JEE Main: Thermal Properties of Matter

Revise these one-line facts from the NCERT chapter just before the exam.

• t_F = (9/5)t_C + 32; T = t_C + 273.15.
• Triple point of water: 273.16 K.
• α_a = 2α_l; α_v = 3α_l; for an ideal gas α_v = 1/T.
• Water has maximum density at 4 °C.
• Thermal stress = Yα_lΔT.
• Specific heat of water = 4186 J kg⁻¹ K⁻¹.
• L_f (ice) = 3.33 × 10⁵ J kg⁻¹; L_v (water) = 22.6 × 10⁵ J kg⁻¹.
• Boiling point rises with pressure.
• H = KAΔT/L for conduction.
• Convection happens only in fluids; radiation needs no medium.
• λ_mT = 2.9 × 10⁻³ m K (Wien).
• H = AeσT⁴, σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴ (Stefan-Boltzmann).
• Newton’s law of cooling holds for small temperature differences.

Common Mistakes to Avoid

Watch for these mix-ups when you answer questions on this chapter.

• Treating heat and temperature as the same thing. Heat is energy in transit; temperature is a measure of hotness.
• Writing α_v = 2α_l. Volume expansion is 3α_l; area expansion is 2α_l.
• Saying water is densest at 0 °C. It is densest at 4 °C.
• Raising the temperature during a phase change in calculations. Temperature stays constant while latent heat is absorbed or released.
• Using Celsius temperatures in the Stefan-Boltzmann law. T must be in kelvin.
• Applying Newton’s law of cooling to large temperature differences. It is valid only for small differences.
• Calling the cooling of a hot bar under running water convection. NCERT notes the bar loses heat by conduction to the water.

Thermal Properties of Matter Notes PDF and Related Pages

Download the AglaSem Class 11 Physics notes on Properties of Matter (key notes and important questions with answers) free: View PDF. This PDF covers the whole Properties of Solids and Liquids unit; its theory pages on heat cover thermal radiation (Stefan’s and Wien’s laws), and its question bank includes thermal expansion, specific heat, latent heat and conduction.

• All chapters: Physics notes for NEET and JEE Main
• Full topic list: NEET syllabus and JEE Main syllabus
• Practice: NEET question papers and JEE Main question papers
• Source text: NCERT Chapter 10 (NCERT, Class 11 Physics Part II)

Physics Notes for NEET and JEE Main: All Chapters

• Units and Measurement
• Motion in a Straight Line
• Motion in a Plane
• Laws of Motion
• Work, Energy and Power
• Systems of Particles and Rotational Motion
• Gravitation
• Mechanical Properties of Solids
• Mechanical Properties of Fluids
• Thermodynamics
• Kinetic Theory of Gases
• Oscillations
• Waves
• Thermal Properties of Matter
• Electric Charges and Fields
• Electrostatic Potential and Capacitance
• Current Electricity
• Moving Charges and Magnetism
• Magnetism and Matter
• Electromagnetic Induction
• Electromagnetic Waves
• Ray Optics and Optical Instruments
• Wave Optics
• Dual Nature of Radiation and Matter
• Atoms
• Nuclei
• Semiconductor Electronics

All chapters with key points and notes PDFs are on the Physics notes for NEET and JEE Main page.

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