CBSE Class 10 Physics Complete Notes: All Chapters for Board Exam 2026

Mastering CBSE Class 10 Physics is essential for scoring top marks in the 2026 Science board exam. Physics accounts for approximately 25 out of the 80 marks in the theory paper. This guide provides comprehensive, NCERT-aligned chapter-wise notes, fundamental formulas, ray diagram rules, sign conventions, and verified solutions to recurring board questions to streamline your revision for the 2026 board exam.

Key Concepts

The CBSE Class 10 Physics syllabus comprises four fundamental chapters: Light – Reflection and Refraction, The Human Eye and the Colourful World, Electricity, and Magnetic Effects of Electric Current. Understanding core derivations, circuit laws, and optical principles is critical for both theoretical and numerical problem-solving.

1. Light – Reflection and Refraction

Light exhibits rectilinear propagation in homogeneous media and undergoes reflection and refraction at interfaces.

• Laws of Reflection:
  1. The incident ray, reflected ray, and normal at the point of incidence all lie in the same plane.
  2. The angle of incidence is equal to the angle of reflection (∠i = ∠r).
• Mirror Formula and Magnification:

  For spherical mirrors of focal length f, object distance u, and image distance v:

  1/f = 1/v + 1/u

  Magnification: m = h'/h = −v/u (where h is object height and h' is image height).

• Refraction & Snell's Law:

  When light travels obliquely from one transparent medium to another, it bends due to a change in speed. Snell's law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media:

  sin i / sin r = constant = n₂₁ = v₁ / v₂

• Lens Formula and Power of a Lens:

  For thin spherical lenses:

  1/f = 1/v − 1/u

  Magnification: m = h'/h = v/u

  Power of a lens (P): P = 1 / f (in metres). The SI unit of lens power is the dioptre (D). Convex lenses have positive power (+D), whereas concave lenses have negative power (−D).

2. The Human Eye and the Colourful World

This chapter examines the optical structure of the human eye, refractive vision defects, and natural atmospheric optical phenomena.

• Defects of Vision and Corrections:
  • Myopia (Near-sightedness): Image forms in front of the retina. Corrected using a concave lens of suitable power.
  • Hypermetropia (Far-sightedness): Image forms behind the retina. Corrected using a convex lens.
  • Presbyopia: Gradual reduction in accommodation power due to aging ciliary muscles. Corrected using bifocal lenses.
• Dispersion through a Glass Prism: Splitting of white light into its component spectrum (VIBGYOR) because different wavelengths refract by different angles; red light bends the least, while violet bends the most.
• Atmospheric Refraction: Responsible for the twinkling of stars, advanced sunrise (2 minutes before actual sunrise), and delayed sunset (2 minutes after actual sunset).
• Scattering of Light & Tyndall Effect: Fine atmospheric particles scatter shorter wavelengths (blue) much more effectively than longer wavelengths (red), giving the clear sky its blue appearance. During sunrise and sunset, sunlight traverses a thicker atmospheric path, leaving predominantly longer red wavelengths unscattered.

3. Electricity

Electricity deals with the flow of electric charge, potential difference, resistance networks, and the thermal effects of electric current.

• Electric Current and Potential Difference:

  Electric current (I) is the rate of flow of electric charge (Q): I = Q / t (SI unit: Ampere, A).

  Electric potential difference (V) between two points is the work done (W) in moving a unit positive charge from one point to the other: V = W / Q (SI unit: Volt, V).

• Ohm's Law:

  The current flowing through a metallic conductor is directly proportional to the potential difference across its terminals, provided physical conditions such as temperature remain constant:

  V = I × R

• Factors Affecting Resistance:

  Resistance of a uniform conductor is directly proportional to its length (l) and inversely proportional to its cross-sectional area (A):

  R = ρ × (l / A) (where ρ is electrical resistivity in Ω·m).

• Combination of Resistors:
  • Series: R_eq = R₁ + R₂ + R₃ (Current remains identical through all resistors; voltage divides).
  • Parallel: 1/R_eq = 1/R₁ + 1/R₂ + 1/R₃ (Voltage remains identical across all resistors; current divides).
• Joule's Law of Heating & Electrical Power:

  Heat produced in a resistor: H = I²Rt = VIt = (V²/R)t

  Electric Power: P = VI = I²R = V² / R (SI unit: Watt, W). Commercial unit of energy is 1 kilowatt-hour (kWh) = 3.6 × 10⁶ Joules.

4. Magnetic Effects of Electric Current

An electric current produces an associated magnetic field in surrounding space.

• Magnetic Field Lines: Continuous closed loops that emerge from the North pole and enter the South pole outside a magnet, while directing from South to North inside the magnet. Field lines never intersect because at any single intersection point, the magnetic compass needle would have to point in two directions simultaneously, which is impossible.
• Rules and Laws:
  • Right-Hand Thumb Rule: If you hold a current-carrying straight conductor in your right hand with the thumb pointing in the direction of current, your curled fingers indicate the direction of magnetic field lines.
  • Fleming's Left-Hand Rule: Used to determine the direction of force acting on a current-carrying conductor placed in an external magnetic field (Thumb = Motion/Force, Forefinger = Magnetic Field, Center finger = Current).
• Domestic Electric Circuits: Standard Indian household circuits supply 220 V AC at 50 Hz using three wires: Live wire (red/brown, 220 V), Neutral wire (black/blue, 0 V), and Earth wire (green/yellow, low-resistance safety ground). Household appliances are connected in parallel to ensure independent control and full operating voltage.

Important CBSE Questions with Answers

These questions are curated from official CBSE question banks and recent board examinations to help you understand standard marking schemes and precise answer presentation.

Question 1

Q: Define the SI unit of electric current. What does one ampere mean?

Answer: The SI unit of electric current is the ampere (A). One ampere is defined as the flow of one coulomb of charge through a cross-section of a conductor in one second, expressed as I = Q / t (where 1 A = 1 C / 1 s = 1 C·s⁻¹).

Question 2

Q: Define 1 watt of power. How is electrical power related to voltage and current?

Answer: One watt (1 W) of power is the rate of energy consumption in an electric circuit when a current of 1 ampere flows under a potential difference of 1 volt (1 W = 1 J / 1 s = 1 V × 1 A). Electrical power is related to voltage and current by the relation P = V × I.

Question 3

Q: Define the refractive index of a medium. Write its SI unit.

Answer: The absolute refractive index (n) of a medium is defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v):

n = c / v

Because it is a ratio of two identical physical quantities (speeds), the refractive index is a dimensionless constant and has no SI unit.

Question 4

Q: What is the power of a lens? Define its SI unit.

Answer: The power of a lens is the measure of the degree of convergence or divergence of light rays achieved by it, defined mathematically as the reciprocal of its focal length in metres: P = 1 / f (in metres). The SI unit of lens power is the Dioptre (D), where 1 Dioptre (1 D) is the power of a lens with a focal length of 1 metre (1 D = 1 m⁻¹).

Question 5

Q: What is the direction of magnetic field lines inside a bar magnet?

Answer: Inside a bar magnet, the magnetic field lines run from the South pole to the North pole. (Outside the magnet, they travel from the North pole to the South pole, forming continuous closed loops).

Question 6

Q: State Ohm's Law. Write the formula and define each term.

Answer: Ohm's Law states that the current flowing through a conductor is directly proportional to the potential difference across its ends, provided temperature and other physical conditions remain constant.

Formula: V = I × R

• V: Potential difference across the conductor (in Volts, V)
• I: Electric current flowing through the conductor (in Amperes, A)
• R: Electrical resistance of the conductor (in Ohms, Ω)

Question 7

Q: A resistor of resistance R is connected across a battery of 6V. If the current is 0.5 A, find the value of R.

Answer:

Given:

• Potential difference (V) = 6 V
• Electric current (I) = 0.5 A

Formula: By Ohm's Law, V = I × R ⇒ R = V / I

Calculation: R = 6 / 0.5 = 12 Ω

The value of resistance R is 12 Ω.

Question 8

Q: Explain why tungsten is used for making filaments of electric lamps.

Answer: Tungsten is used almost exclusively for filaments of incandescent lamps because:

1. Extremely High Melting Point: Tungsten has a very high melting point (approximately 3380°C), preventing it from melting even at incandescent white-hot temperatures.
2. High Resistivity: It exhibits high resistivity, enabling it to produce substantial thermal energy and glow brightly via Joule heating without burning or oxidizing rapidly in an inert argon/nitrogen atmosphere.

How to Prepare for This Topic

To maximize your score in CBSE Class 10 Physics for the 2026 board examinations, follow these systematic preparation strategies:

1. Master Sign Conventions & Ray Diagrams: Practice the New Cartesian Sign Convention consistently. Ensure all optical ray diagrams are drawn with sharp pencils, labeled focal points, and clear directional arrows indicating ray propagation to avoid mark deductions.
2. Memorize Standard Units and Conversion Rules: Maintain a quick-reference formula chart. Always convert units to the SI system before computing numerical problems (e.g., converting focal lengths from centimetres to metres before calculating power in dioptres).
3. Prioritize Conceptual & Phenomenon-Based Explanations: Questions assessing everyday applications—such as atmospheric dispersion, why hazards use red lights, reasons for appliance earthing, and fuse ratings—form a core portion of CBSE Section B and C question papers.
4. Practice Timed Chapter-Wise Numericals: Dedicated practice on resistor combinations, power dissipation, and lens/mirror magnification builds numerical speed and eliminates step-wise calculation errors. You can generate focused chapter tests using the Theorify QPTool CBSE Question Paper Generator.

Where to Practice More

Consistent mock test evaluation aligned with official CBSE marking rubrics is key to securing an A1 grade in Science. Visit Theorify QPTool to generate unlimited, NCERT-aligned custom Class 10 CBSE practice test papers, competency-based questions, and step-by-step marking schemes tailored for the 2026 board exam.