JEE Main Physics Properties of Solids & Liquids 2027: Elasticity, Fluids & Heat

This is the widest chapter in JEE Main Physics. It hides four mini-chapters under one name: elasticity, fluid mechanics, surface tension and heat transfer. The good news is that each block runs on two or three formulas, and questions are usually short.

Wide is not the same as hard. Break the chapter into four blocks and each one is small.

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Chapter at a Glance

Priority reflects past-paper trends, not an official NTA weightage.

What the NTA Syllabus Covers

• Elastic behaviour, stress-strain, Hooke's law, Young's, bulk and shear moduli
• Fluid pressure, Pascal's law, viscosity, Stokes' law, terminal velocity, streamline and turbulent flow, Bernoulli's principle
• Surface energy and surface tension, angle of contact, excess pressure, drops, bubbles and capillary rise
• Heat, temperature, thermal expansion, specific heat, calorimetry, change of state, latent heat, conduction, convection and radiation

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Master These Topics

1. Elasticity: Stress, Strain and Young's Modulus

Stress is force per unit area, strain is fractional deformation, and Young's modulus is Y = stress / strain = FL / (AΔL).

Worked example: A steel wire (Y = 2 × 10¹¹ N/m²) of length 2 m and area 1 mm² carries a 100 N load. Extension = FL / (AY) = 100 × 2 / (10⁻⁶ × 2 × 10¹¹) = 10⁻³ m = 1 mm.

Energy stored per unit volume is ½ × stress × strain.

2. Fluids: Bernoulli, Continuity and Terminal Velocity

• Continuity: A₁v₁ = A₂v₂ for incompressible flow.
• Bernoulli: P + ½ρv² + ρgh = constant along a streamline.
• Torricelli's law: speed of efflux from a hole at depth h is v = √(2gh). At h = 5 m, v = 10 m/s.

Viscous drag on a small sphere is given by Stokes' law: F = 6πηrv. A falling sphere reaches terminal velocity v_t = 2r²(ρ − σ)g / 9η, where ρ is the sphere's density and σ the liquid's. Because v_t ∝ r², doubling the radius quadruples the terminal velocity.

Trap: Bernoulli applies to non-viscous, incompressible, steady flow. It does not account for viscosity losses.

3. Surface Tension and Capillary Rise

Surface tension T is force per unit length (or energy per unit area). Excess pressure across a curved surface:

• Liquid drop: ΔP = 2T/r
• Soap bubble (two surfaces): ΔP = 4T/r

Worked example: A soap bubble of radius 1 cm with T = 0.03 N/m has excess pressure 4 × 0.03 / 0.01 = 12 Pa.

Capillary rise is h = 2T cosθ / (rρg), inversely proportional to tube radius.

4. Heat: Calorimetry and Transfer

Heat needed for a temperature change is Q = mcΔT. For a phase change it is Q = mL. Melting 10 g of ice at 0 °C needs 10 × 80 = 800 cal.

Conduction rate: Q/t = kAΔT / L. Stefan's law says radiated power is P = σAT⁴ for a black body. Newton's law of cooling: rate of cooling is proportional to the temperature difference from the surroundings, for small differences.

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Common Traps to Avoid

• Using 2T/r for a soap bubble. It has two surfaces, so use 4T/r.
• Forgetting that terminal velocity depends on r squared.
• Applying Bernoulli's equation across a pump or between streamlines with energy input.
• Mixing up specific heat with latent heat during a phase change.

60-Second Revision Sheet

• Y = FL/(AΔL); energy density ½ × stress × strain
• Continuity A₁v₁ = A₂v₂; Torricelli v = √(2gh)
• Drop 2T/r, bubble 4T/r, capillary h = 2T cosθ/(rρg)
• Q = mcΔT, Q = mL, conduction kAΔT/L

Your Study Plan

1. Day 1: elasticity and wire-stretching numericals.
2. Day 2: fluid statics and dynamics, Bernoulli and Torricelli.
3. Day 3: surface tension, viscosity and terminal velocity.
4. Day 4: calorimetry and heat transfer, then a mixed timed set.

Practice Properties of Solids & Liquids Questions Free → (opens in a new tab)

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Continue Your Physics Journey

• Previous chapter: Gravitation
• Next chapter: Thermodynamics
• All 20 JEE Main Physics chapters
• Complete JEE Main Syllabus 2027 guide

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