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ICSE Class 10 Science★ ICSE Class 10 Science (Physics) · ~25 marks · Board: ICSE

Physics — Force, Machines, Light, Sound, Electricity & Modern Physics

ICSE Class 10 Physics: FORCE and its turning effect. SIMPLE MACHINES that amplify our strength. REFRACTION and LENSES — how light bends and focuses. SOUND waves. CURRENT ELECTRICITY and HOUSEHOLD CIRCUITS. CALORIMETRY. And the MODERN PHYSICS of RADIOACTIVITY. ICSE Class 10 Science.

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By the end of this chapter you'll be able to…

1Calculate the moment of force (torque) and apply the principle of moments; explain uniform circular motion and centripetal force
2Distinguish classes of levers; calculate mechanical advantage, velocity ratio, and efficiency of simple machines
3Apply Snell's law to refraction problems; describe the formation of images by convex and concave lenses using lens formula and ray diagrams
4Describe properties and uses of sound waves; explain resonance and echo
5Solve electrical circuit problems involving Ohm's law, resistors in series and parallel, and electrical energy and power
6Explain calorimetry and solve heat transfer problems using specific heat capacity
7Describe properties of alpha, beta, and gamma radiation; apply the half-life concept

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Why this chapter matters

ICSE Physics paper carries approximately 80 marks, of which this file's topics — force/machines, light (refraction/lenses), sound, electricity, and radioactivity — account for nearly 25 marks. Electricity (resistors, house wiring, calorimetry) is the highest-scoring topic and is entirely formula-based: learn the formulas, practice substitution. Machines (levers and pulleys) are conceptually straightforward and score 6–8 marks. Refraction and lenses appear in every paper. Radioactivity questions are short and specific — learn the alpha/beta/gamma properties table and half-life formula.

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Physics — Force, Machines, Light, Sound, Electricity & Radioactivity

1. Force

Turning Effect (Moment of Force)

Moment = Force × Perpendicular distance from pivot. Unit: Nm. The longer the lever arm, the GREATER the turning effect.

Centre of Gravity

Point where the ENTIRE WEIGHT of the body appears to act. For uniform objects: at the geometric centre.

Uniform Circular Motion

Object moves in a CIRCLE at CONSTANT SPEED. Velocity CHANGES (direction changes continuously → acceleration). Centripetal force acts TOWARD the centre.

2. Work, Power and Energy

Work = Force × Displacement (in direction of force). Unit: Joule (J). 1 J = 1 N × 1 m.
Power = Work / Time. Unit: Watt (W). 1 W = 1 J/s.
Energy: Capacity to do work. KE = ½mv². PE = mgh. Energy is CONSERVED (transforms, not destroyed).

3. Machines

A MACHINE makes work EASIER (but does NOT reduce total work — it trades force for distance).

Key Terms

Load (L) : The weight being lifted. Effort (E) : The force applied.
Mechanical Advantage (MA) = Load / Effort.
Velocity Ratio (VR) = Distance moved by effort / Distance moved by load.
Efficiency (η) = (MA / VR) × 100%. Always < 100% (friction).

Levers

Class	Order	Example
I	Fulcrum BETWEEN load and effort	See-saw, scissors, crowbar
II	Load BETWEEN fulcrum and effort	Wheelbarrow, nutcracker
III	Effort BETWEEN fulcrum and load	Tweezers, tongs, human forearm

Pulleys

Single FIXED pulley: MA = 1 (only changes DIRECTION). Single MOVABLE pulley: MA = 2. Block and tackle: MA = number of supporting strands.

4. Refraction and Lenses

Refraction

Bending of light when it passes from one medium to another (SPEED CHANGES).

Laws of Refraction

Snell's Law: sin i / sin r = constant (refractive index n = c/v).

Refractive Index: n = speed in air / speed in medium

Lenses

	Convex (Converging)	Concave (Diverging)
Effect	Converges parallel rays to a FOCUS	Diverges parallel rays
Images	Real/Virtual. Magnified.	Always VIRTUAL, DIMINISHED, ERECT.

Lens Formula: 1/f = 1/v — 1/u. Magnification: m = v/u = hᵢ/hₒ.

Sign convention: u = —. f: convex = +, concave = —. v: real = +, virtual = —.

Uses of Lenses

Convex: Magnifying glass. Camera. Human EYE. Microscope.
Concave: Correcting MYOPIA (short-sightedness).

5. Spectrum and Scattering

White light DISPERSES into 7 colours (VIBGYOR) through a PRISM.
Scattering: Blue sky (shorter wavelengths scatter more). Red sunset (longer wavelengths — light travels through more atmosphere).

Electromagnetic Spectrum

Radio → Microwave → Infrared → Visible → UV → X-ray → Gamma (increasing frequency).

Infrared and Ultraviolet

IR: Heat radiation. Remote controls. Night vision.
UV: From sun. Ozone layer absorbs it. Causes sunburn, skin cancer.

6. Sound

Nature

Sound is a MECHANICAL WAVE. Requires a MEDIUM (solid, liquid, gas). CANNOT travel through vacuum. Longitudinal wave (compressions and rarefactions).

Characteristics

Pitch (frequency — Hz). Loudness (amplitude). Timbre/Quality (waveform).

Speed in Different Media: Solid > Liquid > Gas

Reflection of Sound — Echo

Echo = reflected sound. Heard distinctly if time gap ≥ 0.1 s. Distance = (Speed × Time) / 2.

Ultrasound and SONAR

Ultrasound > 20,000 Hz. Bats. Medical imaging. SONAR (Sound Navigation and Ranging) — used in ships to detect depth.

7. Current Electricity

Ohm's Law: V = IR

V = Potential Difference (Volts). I = Current (Amperes). R = Resistance (Ohms, Ω).

Resistance: R = ρL/A

R ∝ Length. R ∝ 1/Area. ρ = resistivity (property of material).

EMF (Electromotive Force) vs. Terminal Voltage

EMF = energy supplied per unit charge. When current flows: V_terminal = EMF — Ir (r = internal resistance).

Electrical Power: P = VI = I²R = V²/R

Unit: Watt. 1 kWh = 1 unit = 3.6 × 10⁶ J.

Combinations of Resistors

Series: Rₑ = R₁ + R₂ + R₃. Same current. Voltage divides.
Parallel: 1/Rₑ = 1/R₁ + 1/R₂ + 1/R₃. Same voltage. Current divides.

8. Household Circuits

Mains supply: 220 V AC, 50 Hz. Colour codes: LIVE (red/brown). NEUTRAL (black/blue). EARTH (green/yellow).
Earthing: Connects appliance body to earth. Prevents electric shock.
FUSE: Melts when current is TOO HIGH (overload or short circuit). SELF-SACRIFICING protection.
Switch: ALWAYS in the LIVE wire.

9. Electromagnetism

Magnetic Effect of Current

Current through a conductor → MAGNETIC FIELD. Right-hand thumb rule. Solenoid = coil of wire → acts like a bar magnet. Electromagnet: Soft iron core. Strength increased by: more turns, more current.

Fleming's Left Hand Rule (Motor Effect)

Conductor in magnetic field → FORCE. Thumb = Force (Motion). Index finger = Field (N→S). Middle finger = Current (+ to —). DC motor.

Electromagnetic Induction (Generator Effect)

CHANGING magnetic field → induced current. Faraday's Law. AC generator (dynamo). Transformer: Vₚ/Vₛ = Nₚ/Nₛ = Iₛ/Iₚ.

10. Calorimetry (Heat)

Specific Heat Capacity (c)

Heat required to raise 1 kg by 1°C. Q = mcΔθ. Water has HIGH c (4200 J/kg°C) — best coolant.

Latent Heat

Heat absorbed/released during CHANGE OF STATE — NO temperature change. Latent heat of fusion (ice → water). Latent heat of vaporisation (water → steam).

Calorimeter Principle

Heat LOST by hot body = Heat GAINED by cold body + calorimeter. SOLVE for unknown specific heat.

11. Radioactivity

Discovery: Henri Becquerel (1896). Marie Curie: named 'radioactivity.'

Three Types of Radiation

Type	Nature	Penetrating Power	Stopped By
Alpha (α)	Helium nucleus. +2 charge.	LEAST.	Paper.
Beta (β)	Electron / positron. — charge.	Moderate.	Few mm of aluminium.
Gamma (γ)	Electromagnetic wave. No charge.	HIGHEST.	Thick lead/concrete.

Nuclear Reactions

Fission (splitting heavy nucleus → energy. Atomic bomb. Nuclear reactor).
Fusion (combining light nuclei → energy. Hydrogen bomb. Sun's energy).

Background Radiation

Natural (cosmic rays, rocks, radon gas). Man-made (medical X-rays, nuclear industry).

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Force, Machines and Circular Motion

MOMENT OF FORCE = Force × Perpendicular distance from pivot. Unit: Nm. PRINCIPLE OF MOMENTS: Sum of clockwise moments = Sum of anticlockwise moments (at equilibrium). MECHANICAL ADVANTAGE (MA) = Load / Effort = VR × Efficiency / 100. VELOCITY RATIO (VR) = Effort distance / Load distance. EFFICIENCY (η) = (MA / VR) × 100%. CENTRIPETAL FORCE = mv²/r (directed toward centre). CENTRIPETAL ACCELERATION = v²/r.

LEVERS: Class I — fulcrum between effort and load (scissors, seesaw). MA can be > or < 1. Class II — load between fulcrum and effort (wheelbarrow, nutcracker). MA always > 1. Class III — effort between fulcrum and load (forearm, broom). MA always < 1. ICSE tests: identify the class and calculate MA given effort arm and load arm lengths.

Refraction and Lenses

SNELL'S LAW: n₁ sin θ₁ = n₂ sin θ₂. REFRACTIVE INDEX: n = sin i / sin r = speed in vacuum / speed in medium = c/v. LENS FORMULA: 1/v − 1/u = 1/f. MAGNIFICATION: m = v/u = height of image / height of object. POWER OF LENS: P = 1/f (in metres). Unit: Dioptre (D). Positive P → converging lens. Negative P → diverging lens. CRITICAL ANGLE: sin C = 1/n (for total internal reflection when n₂ < n₁).

SIGN CONVENTION (New Cartesian): All distances measured from the OPTICAL CENTRE. Distances in the direction of incident light = POSITIVE. Against incident light = NEGATIVE. Object is ALWAYS to the left → u is NEGATIVE for real objects. For convex lens: f is POSITIVE. For concave lens: f is NEGATIVE. ICSE tests: Given object distance and focal length, find image distance and nature (real/virtual, erect/inverted, magnified/diminished).

Current Electricity

OHM'S LAW: V = IR. RESISTANCE in SERIES: R_total = R₁ + R₂ + R₃ (current same through all). RESISTANCE in PARALLEL: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃ (voltage same across all). ELECTRICAL POWER: P = VI = I²R = V²/R. Unit: Watt (W). ELECTRICAL ENERGY: E = P × t = VIt. Unit: Joule (J). 1 kWh = 3.6 × 10⁶ J. COST: units consumed = P(kW) × t(hours). HOUSE WIRING: Live (red/brown), Neutral (black/blue), Earth (green/yellow). MCB/Fuse — in LIVE wire only.

PARALLEL CIRCUITS: For two resistors in parallel, the combined resistance is LESS than the smaller individual resistance. Formula shortcut for two parallel resistors: R_total = (R₁ × R₂) / (R₁ + R₂). SAFETY: Earth wire protects against electric shock (provides path for fault current). Fuse protects against short circuits. In house wiring, EACH appliance is connected in PARALLEL with the mains supply (so they operate independently at the same voltage).

Calorimetry and Heat

HEAT EQUATION: Q = mcΔT, where m = mass (kg or g), c = specific heat capacity (J/kg°C or J/g°C), ΔT = temperature change. HEAT LOST = HEAT GAINED (principle of calorimetry — for a mixture, no heat exchanged with surroundings). LATENT HEAT: Q = mL (heat absorbed/released during change of state — no temperature change). Specific Latent Heat of Fusion of ice: L_f = 336 J/g. Specific Latent Heat of Vaporisation of water: L_v = 2260 J/g.

CALORIMETRY PROBLEMS: 'Hot object A is mixed with cold object B; find the final temperature.' Set up: heat lost by A = heat gained by B. m_A × c_A × (T_A − T_f) = m_B × c_B × (T_f − T_B). Solve for T_f. If state change is involved (e.g., ice melting), include latent heat: heat to melt ice = m_ice × L_f, then heat to raise ice-water to T_f.

Radioactivity

HALF-LIFE (T½): Time for half the radioactive nuclei to decay. After n half-lives: N = N₀ × (1/2)ⁿ. ALPHA (α): Helium nucleus (₂⁴He). Charge = +2. Least penetrating (stopped by paper). BETA (β): High-speed electron (₋₁⁰e). Charge = −1. Stopped by thin aluminium. GAMMA (γ): Electromagnetic wave. No charge. Most penetrating (needs thick lead/concrete). NUCLEAR EQUATIONS: In α-decay: mass number decreases by 4, atomic number decreases by 2. In β-decay: mass number unchanged, atomic number increases by 1.

HALF-LIFE CALCULATION: If T½ = 20 years and you start with 160 g, after 60 years: n = 60/20 = 3 half-lives. Remaining = 160 × (1/2)³ = 160/8 = 20 g. NUCLEAR EQUATIONS: Always verify that BOTH mass numbers and atomic numbers BALANCE on both sides. α-decay example: ₉₂²³⁸U → ₉₀²³⁴Th + ₂⁴He. β-decay: ₆²³C → ₇²³N + ₋₁⁰e.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Using the wrong sign for u (object distance) in the lens formula

✓ In the New Cartesian sign convention, the object is always to the LEFT of the lens, and all distances are measured from the optical centre. The object distance u is ALWAYS NEGATIVE for real objects (since the object is to the left — against the direction of incident light). Write u = −(given value) before substituting. Example: If object is 30 cm from a convex lens (f = +20 cm), u = −30. Then 1/v = 1/f + 1/u = 1/20 + 1/(−30) = 3/60 − 2/60 = 1/60. v = +60 cm (positive → real image).

WATCH OUT

✗ Adding resistances in parallel instead of using the reciprocal formula

✓ For parallel resistors, you CANNOT directly add the resistances. The RECIPROCAL formula applies: 1/R_total = 1/R₁ + 1/R₂. Find R_total by taking the reciprocal of the sum of reciprocals. Quick check: R_total for parallel resistors is ALWAYS LESS than the smallest individual resistor. If you get R_total > smallest R, you made an error. For two resistors, use the shortcut: R_total = (R₁ × R₂)/(R₁ + R₂).

WATCH OUT

✗ Confusing alpha and beta decay effects on atomic number

✓ ALPHA decay: loses ₂⁴He → mass number decreases by 4, atomic number decreases by 2. BETA decay: a neutron converts to a proton and emits an electron (β particle) → mass number UNCHANGED, atomic number INCREASES by 1 (one more proton). Remember: α emission = loss of 2 protons + 2 neutrons. β emission = neutron becomes proton (count of protons goes up by 1). Gamma emission: no change in mass or atomic number (just energy released).

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· electricity-series-parallel

Two resistors of 4 Ω and 12 Ω are connected (a) in series, (b) in parallel, across a 24 V battery. Find the total resistance and total current in each case.

▶ Show solution

(a) SERIES: R_total = 4 + 12 = 16 Ω. Current I = V/R = 24/16 = 1.5 A. (b) PARALLEL: 1/R_total = 1/4 + 1/12 = 3/12 + 1/12 = 4/12. R_total = 12/4 = 3 Ω. Current I = V/R = 24/3 = 8 A. Note: Parallel gives much lower resistance and higher current. Check (b) using shortcut: R = (4 × 12)/(4 + 12) = 48/16 = 3 Ω ✓.

Q2MEDIUM· optics-lens-formula

A concave lens of focal length 20 cm is used. An object is placed 30 cm from the lens. Find: (a) the image distance, (b) magnification, (c) nature of the image.

▶ Show solution

Concave lens: f = −20 cm (negative for diverging lens). Object: u = −30 cm. LENS FORMULA: 1/v − 1/u = 1/f. 1/v = 1/f + 1/u = 1/(−20) + 1/(−30) = −3/60 − 2/60 = −5/60. v = −12 cm. (a) Image distance = 12 cm on the SAME side as the object (virtual image). (b) m = v/u = (−12)/(−30) = +0.4. (c) Since m is positive and less than 1: image is VIRTUAL, ERECT, and DIMINISHED. It forms 12 cm to the left of the lens (same side as object). This is always the case for a concave lens with a real object.

Q3HARD· calorimetry-latent-heat

100 g of ice at 0°C is added to 200 g of water at 60°C in an insulated container. Find the final temperature of the mixture. (Specific heat of water = 4.2 J/g°C, Latent heat of fusion of ice = 336 J/g)

▶ Show solution

Step 1: Heat available from water cooling from 60°C to 0°C: Q_available = 200 × 4.2 × 60 = 50,400 J. Step 2: Heat needed to melt all ice: Q_melt = 100 × 336 = 33,600 J. Since Q_available (50,400) > Q_melt (33,600), all ice melts. Step 3: Remaining heat after melting = 50,400 − 33,600 = 16,800 J. This heat raises the temperature of the now-melted water (100 g ice → 100 g water at 0°C). Total water = 100 + 200 = 300 g. 16,800 = 300 × 4.2 × T_f. T_f = 16,800 / 1,260 = 13.33°C. FINAL TEMPERATURE = 13.3°C.

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Physics — Force, Machines, Light, Sound, Electricity & Modern Physics

By the end of this chapter you'll be able to…

Before you start — revise these

Physics — Force, Machines, Light, Sound, Electricity & Radioactivity

1. Force

Turning Effect (Moment of Force)

Centre of Gravity

Uniform Circular Motion

2. Work, Power and Energy

3. Machines

Key Terms

Levers

Pulleys

4. Refraction and Lenses

Refraction

Laws of Refraction

Refractive Index: n = speed in air / speed in medium

Lenses

Lens Formula: 1/f = 1/v — 1/u. Magnification: m = v/u = hᵢ/hₒ.

Uses of Lenses

5. Spectrum and Scattering

Electromagnetic Spectrum

Infrared and Ultraviolet

6. Sound

Nature

Characteristics

Speed in Different Media: Solid > Liquid > Gas

Reflection of Sound — Echo

Ultrasound and SONAR

7. Current Electricity

Ohm's Law: V = IR

Resistance: R = ρL/A

EMF (Electromotive Force) vs. Terminal Voltage

Electrical Power: P = VI = I²R = V²/R

Combinations of Resistors

8. Household Circuits

9. Electromagnetism

Magnetic Effect of Current

Fleming's Left Hand Rule (Motor Effect)

Electromagnetic Induction (Generator Effect)

10. Calorimetry (Heat)

Specific Heat Capacity (c)

Latent Heat

Calorimeter Principle

11. Radioactivity

Discovery: Henri Becquerel (1896). Marie Curie: named 'radioactivity.'

Three Types of Radiation

Nuclear Reactions

Background Radiation

Key formulas & results

Common mistakes & fixes

Practice problems

ICSE marks blueprint

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