physics

name	physics
description	CBSE Grade 10 Physics — Light, Electricity, Magnetism. Covers chapters 9-12 of Science. Activate for physics concepts, ray diagrams, circuit problems, and board exam patterns.

Physics — CBSE Grade 10 Science

Syllabus Coverage (2026–27)

Unit	Chapters	Marks
III. Natural Phenomena	Ch 9: Light – Reflection and Refraction, Ch 10: The Human Eye and the Colourful World	12
IV. Effects of Current	Ch 11: Electricity, Ch 12: Magnetic Effects of Electric Current	13
Physics Total	4 Chapters	~25

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Chapter 9: Light – Reflection and Refraction

Key Concepts

Reflection:

• Laws of reflection: (i) angle of incidence = angle of reflection, (ii) incident ray, reflected ray, normal — all in same plane
• Concave mirror: converging, real images (except when object between F and P)
• Convex mirror: diverging, always virtual/erect/diminished images
• Mirror formula and magnification

Refraction:

• Laws of refraction (Snell's Law): n₁ sin i = n₂ sin r
• Refractive index: n = speed in vacuum / speed in medium
• Convex lens: converging, real images (except when object between F and O)
• Concave lens: diverging, always virtual/erect/diminished images
• Lens formula and magnification
• Power of lens

Key Formulas

MIRROR FORMULA: 1/v + 1/u = 1/f
MAGNIFICATION (mirror): m = -v/u = h'/h
Sign Convention (New Cartesian):
  - Object always on left → u is always negative
  - Concave mirror: f is negative, Convex mirror: f is positive

LENS FORMULA: 1/v - 1/u = 1/f
MAGNIFICATION (lens): m = v/u = h'/h
  - Convex lens: f is positive, Concave lens: f is negative

POWER: P = 1/f (f in metres) → unit: Dioptre (D)
REFRACTIVE INDEX: n = sin i / sin r = c/v
n₂₁ = n₂/n₁ = v₁/v₂

COMBINED POWER: P = P₁ + P₂ + P₃ + ...

Image Formation Tables

Concave Mirror:

Object Position	Image Position	Nature	Size
At infinity	At F	Real, inverted	Highly diminished
Beyond C	Between F and C	Real, inverted	Diminished
At C	At C	Real, inverted	Same size
Between C and F	Beyond C	Real, inverted	Enlarged
At F	At infinity	Real, inverted	Highly enlarged
Between F and P	Behind mirror	Virtual, erect	Enlarged

Convex Lens:

Object Position	Image Position	Nature	Size
At infinity	At F₂	Real, inverted	Highly diminished
Beyond 2F₁	Between F₂ and 2F₂	Real, inverted	Diminished
At 2F₁	At 2F₂	Real, inverted	Same size
Between F₁ and 2F₁	Beyond 2F₂	Real, inverted	Enlarged
At F₁	At infinity	Real, inverted	Highly enlarged
Between F₁ and O	Same side	Virtual, erect	Enlarged

Common Exam Traps

• Sign convention errors — most common: forgetting u is always negative
• Not drawing the principal axis, lens/mirror properly in ray diagrams
• Confusing mirror magnification formula (negative sign) with lens formula
• Power of lens: forgetting to convert f to metres before calculating

Diagram Requirements (MUST draw in board exam)

1. Ray diagram for concave mirror (at least 2 positions)
2. Ray diagram for convex lens (at least 2 positions)
3. At least 2 rays must be drawn for locating image
4. Label: Principal axis, F, C/2F, object, image

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Chapter 10: The Human Eye and the Colourful World

Key Concepts

• Structure of human eye: cornea, iris, pupil, lens, retina, optic nerve
• Power of accommodation: ability to focus on near and far objects
• Defects of vision:
  • Myopia (near-sightedness): corrected by concave lens
  • Hypermetropia (far-sightedness): corrected by convex lens
  • Presbyopia: corrected by bifocal lens
• Atmospheric refraction: twinkling of stars, advanced sunrise/delayed sunset
• Dispersion: splitting of white light into 7 colours (VIBGYOR)
• Scattering of light: Tyndall effect, blue sky, red sunset

Key Formulas

MYOPIA correction: f = -far point distance (concave lens)
HYPERMETROPIA correction: f = near point distance (convex lens)
VIBGYOR: Violet, Indigo, Blue, Green, Yellow, Orange, Red
  - Violet has shortest wavelength, highest frequency, maximum deviation
  - Red has longest wavelength, lowest frequency, minimum deviation

Common Exam Traps

• Confusing myopia and hypermetropia corrections
• Not explaining WHY stars twinkle (atmospheric refraction due to changing density)
• Forgetting to mention Tyndall effect as cause of scattering phenomena

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Chapter 11: Electricity

Key Concepts

• Electric current: I = Q/t (rate of flow of charge)
• Potential difference: V = W/Q (work done per unit charge)
• Ohm's Law: V = IR
• Resistance: R = ρl/A
• Series and parallel combinations
• Heating effect of current: Joule's law
• Electric power and energy

Key Formulas

CURRENT: I = Q/t (Ampere = Coulomb/second)
POTENTIAL DIFFERENCE: V = W/Q (Volt = Joule/Coulomb)
OHM'S LAW: V = IR
RESISTANCE: R = V/I (Ohm, Ω)
RESISTIVITY: R = ρl/A (ρ in Ω·m)

SERIES COMBINATION:
  R_total = R₁ + R₂ + R₃ + ...
  Same current through all resistors
  V_total = V₁ + V₂ + V₃

PARALLEL COMBINATION:
  1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ...
  Same voltage across all resistors
  I_total = I₁ + I₂ + I₃

JOULE'S LAW OF HEATING: H = I²Rt = VIt = V²t/R
ELECTRIC POWER: P = VI = I²R = V²/R (Watt)
ELECTRIC ENERGY: E = P × t = VIt (Joule)
1 kWh = 3.6 × 10⁶ J

Circuit Diagram Symbols

—/\/\/\— Resistor      —|⊕|— Ammeter (series)
—||— Cell               —⊗— Voltmeter (parallel)
—|  |— Battery          ○/ ○ Switch (open)
—→— Current direction   ●—● Switch (closed)

Common Exam Traps

• Ammeter connected in SERIES, Voltmeter in PARALLEL — mixing these up
• Not drawing circuit diagrams neatly with proper symbols
• Confusing kWh and Joule conversions
• Forgetting that in parallel: total resistance < smallest individual resistance
• Not accounting for internal resistance when stated in problems

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Chapter 12: Magnetic Effects of Electric Current

Key Concepts

• Magnetic field and field lines
• Right-hand thumb rule (for straight conductor)
• Solenoid: magnetic field like a bar magnet
• Force on current-carrying conductor in magnetic field (Fleming's Left Hand Rule)
• Electromagnetic induction (Faraday's law)
• Fleming's Right Hand Rule (for generators)
• Electric motor and Electric generator (AC and DC)
• Domestic electric circuits: fuse, earthing, short circuit

Key Rules

RIGHT-HAND THUMB RULE:
  Thumb → direction of current
  Fingers (curled) → direction of magnetic field

FLEMING'S LEFT HAND RULE (Motor):
  Forefinger → magnetic Field
  Middle finger → Current
  Thumb → Force/Motion (thrust)

FLEMING'S RIGHT HAND RULE (Generator):
  Thumb → Motion of conductor
  Forefinger → magnetic Field
  Middle finger → induced Current

Key Devices

ELECTRIC MOTOR: Converts electrical energy → mechanical energy
  Uses: Fleming's Left Hand Rule
  Parts: Coil, magnets, split ring commutator, brushes, axle

ELECTRIC GENERATOR: Converts mechanical energy → electrical energy
  Uses: Electromagnetic induction (Fleming's Right Hand Rule)
  AC Generator: slip rings → alternating current
  DC Generator: split ring commutator → direct current

Domestic Circuits

Supply: 220V AC, 50Hz frequency
Fuse: thin wire with low melting point, connected in LIVE wire
Earthing: connected to metal body of appliances
Short circuit: live wire touches neutral wire → very high current → fuse melts
Overloading: too many appliances → current exceeds capacity → fuse melts

Three wires:
  LIVE (red/brown) — high potential
  NEUTRAL (black/blue) — zero potential
  EARTH (green) — safety, connected to ground

Common Exam Traps

• Confusing Left Hand Rule (motor) with Right Hand Rule (generator)
• Not labeling all parts of motor/generator in diagrams
• Forgetting that AC generator uses slip rings, DC uses split rings
• Not mentioning the role of commutator (reverses current direction every half rotation)

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High-Yield Topics (495+ Strategy)

1. Electricity (Ohm's Law + Series/Parallel) — 5M LA question almost guaranteed
2. Light (Mirror/Lens formula + Ray diagrams) — 5M LA in most papers
3. Magnetic Effects (Motor/Generator) — 3-5M diagram-based question
4. Human Eye defects — 2-3M frequently asked
5. Case Study — Often from Electricity or Light chapter

CBSE Question Patterns

1-Mark MCQ Examples:

• "A concave mirror produces a real, inverted image of same size. The object is at: (a) F (b) C (c) Beyond C (d) Between F and C" → Answer: (b)
• "Which of the following has highest resistance? (a) 1Ω (b) 10⁵Ω (c) 10⁻⁵Ω (d) 10²Ω" → Answer: (b)

3-Mark SA Examples:

• "An object is placed at 30 cm from a concave mirror of focal length 15 cm. Find position, nature and size of image."
• "Three resistors of 5Ω, 10Ω and 15Ω are connected in parallel. Find equivalent resistance."

5-Mark LA Examples:

• "Draw ray diagrams for all 6 positions of object in a convex lens."
• "Derive the expression for equivalent resistance when three resistors are connected in (a) series (b) parallel."

Case Study Example:

• Passage about electricity bill of a household → calculate energy consumed, cost, suggest energy-saving measures

Answer Writing Framework for Physics

1. Start with the formula — examiners check for this first
2. Draw diagrams — ray diagrams, circuit diagrams earn dedicated marks
3. Show all substitutions — V = IR, then V = 2 × 5 = 10V
4. Include units in every answer — "R = 5 Ω", "P = 100 W"
5. For derivations — start from basic principle, proceed step by step
6. For diagram-based questions — label every component, use ruler for straight lines

Internal Assessment Notes

Component	Details
Practical Exam	Perform experiments: focal length of concave mirror/convex lens, Ohm's law verification, resistances in series/parallel
Practical viva	Be prepared for "why" questions about the experiment
Record maintenance	All observations with proper tables, calculations, and results