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** |

---

## 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

---

## 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

---

## 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

---

## 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)

---

## 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 |