Physics Notes

PHYSICS NOTES

Physics Notes for SSC, Railway & Competitive Exams

Physics is one of the most important subjects in General Science for SSC, Railway, Banking, Defence, Police and other competitive examinations. These notes explain important concepts, formulas and scientific principles in simple English to help you prepare effectively.

📖 Reading Time: 18–20 Minutes 🎯 SSC | Railway | Banking ⭐ Beginner Friendly 📝 Updated 2026

Introduction

Physics is the branch of science that studies matter, energy, motion, force and the interaction between them. It explains how objects move, why things fall to the ground, how electricity flows, why light travels and how sound is produced.

Physics plays an important role in daily life and is one of the most frequently asked subjects in SSC, Railway, Defence, Banking and State Government examinations.

🎯 Exam Focus
  • SI Units
  • Motion
  • Newton’s Laws of Motion
  • Work, Energy & Power
  • Heat & Temperature
  • Sound
  • Light
  • Electricity
  • Magnetism

SI Units

The International System of Units (SI) is the standard system of measurement used worldwide. Every physical quantity has a standard unit for accurate measurement.

Physical Quantity SI Unit Symbol
Length Metre m
Mass Kilogram kg
Time Second s
Temperature Kelvin K
Electric Current Ampere A
Amount of Substance Mole mol
Luminous Intensity Candela cd
⭐ Important Facts
  • There are seven SI base units.
  • Kelvin is the SI unit of temperature.
  • Ampere is the SI unit of electric current.
  • Kilogram is the SI unit of mass.

📘 Remember

Length → m
Mass → kg
Time → s
Current → A

Physical Quantities

A physical quantity is a measurable property of an object or substance. Physical quantities are classified into two categories.

Type Examples
Scalar Quantity Mass, Time, Speed, Distance, Energy
Vector Quantity Velocity, Force, Acceleration, Momentum
🧠 Remember Scalar = Magnitude Only

Vector = Magnitude + Direction

Motion

Motion is the change in the position of an object with respect to time. If an object changes its position over time, it is said to be in motion.

Types of Motion

  • Linear Motion
  • Circular Motion
  • Rotational Motion
  • Oscillatory Motion
⭐ Examples
  • Moving train → Linear Motion
  • Ceiling fan → Rotational Motion
  • Earth around the Sun → Circular Motion
  • Pendulum → Oscillatory Motion

Speed, Velocity and Acceleration

Quantity Meaning
Speed Distance travelled per unit time.
Velocity Speed in a particular direction.
Acceleration Rate of change of velocity.

📘 Important Formulae

Speed = Distance ÷ Time

Velocity = Displacement ÷ Time

Acceleration = Change in Velocity ÷ Time
🎯 Exam Tip Speed is a Scalar Quantity, whereas Velocity and Acceleration are Vector Quantities.

Quick Revision

  • Speed → Distance ÷ Time
  • Velocity → Speed with Direction
  • Acceleration → Change in Velocity

Newton’s Laws of Motion

Sir Isaac Newton proposed three fundamental laws that explain the motion of objects. These laws form the foundation of classical mechanics.

First Law (Law of Inertia)

An object remains at rest or continues to move with uniform velocity unless acted upon by an external force.

Second Law

The rate of change of momentum is directly proportional to the applied force.

Force = Mass × Acceleration

F = m × a

Third Law

For every action, there is an equal and opposite reaction.

⭐ Examples
  • Seat belt works because of inertia.
  • Walking is possible because of action and reaction.
  • Rocket launch follows Newton’s Third Law.

Quick Revision

  • 1st Law → Inertia
  • 2nd Law → F = ma
  • 3rd Law → Action = Reaction

Force

Force is a push or pull acting on an object that can change its state of rest, motion, speed, direction or shape. The SI unit of force is the Newton (N).

Force is a vector quantity because it has both magnitude and direction.

📘 Formula

Force = Mass × Acceleration

F = m × a
Type of Force Example
Gravitational Force Objects falling towards Earth.
Magnetic Force Attraction between magnets.
Frictional Force Brakes stopping a vehicle.
Muscular Force Pushing a cart.
⭐ Important Facts
  • SI Unit of Force → Newton (N)
  • Force is a Vector Quantity.
  • Force can change both speed and direction of motion.

Quick Revision

  • SI Unit → Newton
  • Formula → F = ma
  • Type → Vector Quantity

Work, Energy and Power

Work is said to be done when a force acts on an object and causes displacement. Energy is the capacity to do work, while Power is the rate at which work is done.

Quantity SI Unit
Work Joule (J)
Energy Joule (J)
Power Watt (W)

📘 Important Formulae

Work = Force × Distance

W = F × d

Power = Work ÷ Time

P = W ÷ t
⭐ Types of Energy
  • Kinetic Energy
  • Potential Energy
  • Heat Energy
  • Electrical Energy
  • Chemical Energy
  • Solar Energy

Quick Revision

  • Work → Joule
  • Energy → Capacity to do Work
  • Power → Watt

Gravitation

Gravitation is the force of attraction between any two objects having mass. Sir Isaac Newton explained the Law of Universal Gravitation.

Gravity is the force by which the Earth attracts objects towards its centre.

📘 Important Formula

Weight = Mass × Gravity

W = m × g
Quantity Value
Acceleration Due to Gravity (g) 9.8 m/s²
SI Unit of Weight Newton (N)
⭐ Important Facts
  • Mass remains constant everywhere.
  • Weight changes with gravity.
  • Astronauts feel weightless because of free fall.

Quick Revision

  • g = 9.8 m/s²
  • Weight = m × g
  • Weight → Newton

Pressure

Pressure is the force acting per unit area. It depends on the magnitude of force and the area over which the force is applied.

📘 Formula

Pressure = Force ÷ Area

P = F ÷ A
Property Value
SI Unit Pascal (Pa)
Scientist Blaise Pascal
⭐ Daily Life Examples
  • Sharp knives cut easily because they exert more pressure.
  • Broad tyres reduce pressure on the ground.
  • Camels have broad feet to walk on sand.

Quick Revision

  • Pressure = Force ÷ Area
  • SI Unit → Pascal

Heat and Temperature

Heat is a form of energy that flows from a hotter object to a colder object. Temperature is the measure of the degree of hotness or coldness of an object.

Heat Temperature
Energy Measure of hotness
Unit → Joule Unit → Kelvin
Flows from hot to cold Does not flow
⭐ Modes of Heat Transfer
  • Conduction
  • Convection
  • Radiation

📘 Temperature Conversion

°C = K − 273

K = °C + 273

Quick Revision

  • Heat → Energy
  • Temperature → Kelvin
  • Three Modes → Conduction, Convection & Radiation

Thermometers

A thermometer is an instrument used to measure temperature. Different thermometers are used for different purposes.

Thermometer Use
Clinical Thermometer Measures human body temperature.
Laboratory Thermometer Measures temperature in laboratories.
Digital Thermometer Electronic temperature measurement.
⭐ Important Facts
  • Normal human body temperature is approximately 37°C (98.6°F).
  • Clinical thermometers are commonly marked from 35°C to 42°C.
  • Digital thermometers are widely used because they are quick and easy to read.

Quick Revision

  • Body Temperature → 37°C
  • SI Unit of Temperature → Kelvin
  • Digital Thermometer → Electronic Device

Sound

Sound is a form of energy produced by vibrating objects. It travels in the form of mechanical waves and requires a material medium (solid, liquid or gas) for propagation. Sound cannot travel through a vacuum.

🎯 Exam Focus Questions are commonly asked about:
  • Characteristics of Sound
  • Speed of Sound
  • Ultrasound
  • Echo
Characteristic Description
Pitch Depends on the frequency of vibration.
Loudness Depends on the amplitude of vibration.
Quality (Timbre) Helps distinguish sounds from different sources.
⭐ Important Facts
  • Sound travels fastest in solids.
  • Sound cannot travel in a vacuum.
  • Ultrasound has a frequency greater than 20,000 Hz.
  • Humans can hear sounds between 20 Hz and 20,000 Hz.

📘 Formula

Speed = Distance ÷ Time

Quick Revision

  • Medium Required → Yes
  • Range of Human Hearing → 20 Hz–20,000 Hz
  • Ultrasound → Above 20,000 Hz

Light

Light is a form of energy that enables us to see objects. It travels in a straight line and does not require a material medium. The speed of light in a vacuum is approximately 3 × 10⁸ m/s.

🎯 Exam Focus Questions are commonly asked about:
  • Reflection
  • Refraction
  • Mirrors
  • Lenses
  • Human Eye
⭐ Important Facts
  • Light can travel through a vacuum.
  • Speed of light is highest in a vacuum.
  • The Sun is the main natural source of light.

Reflection of Light

Reflection is the bouncing back of light into the same medium after striking a surface.

Laws of Reflection

  • The angle of incidence is equal to the angle of reflection.
  • The incident ray, reflected ray and normal lie in the same plane.
⭐ Important Facts
  • A plane mirror forms a virtual, erect and same-sized image.
  • The image distance is equal to the object distance in a plane mirror.

Quick Revision

  • Angle of Incidence = Angle of Reflection
  • Plane Mirror → Virtual Image

Types of Mirrors

Mirror Main Use
Plane Mirror Looking glass.
Concave Mirror Vehicle headlights, shaving mirrors, dentists’ mirrors.
Convex Mirror Rear-view mirrors in vehicles.
🧠 Remember CCV
  • C → Concave → Close-up Image
  • C → Convex → Cars (Rear-view Mirror)

Quick Revision

  • Concave → Headlights
  • Convex → Rear-view Mirror
  • Plane → Looking Glass

Refraction of Light

Refraction is the bending of light when it passes from one transparent medium to another because its speed changes.

⭐ Daily Life Examples
  • A pencil appears bent when placed in water.
  • The bottom of a swimming pool appears shallower.
  • Stars appear to twinkle due to atmospheric refraction.

Quick Revision

  • Refraction → Bending of Light
  • Cause → Change in Speed

Types of Lenses

Lens Characteristic
Convex Lens Converges light rays.
Concave Lens Diverges light rays.
⭐ Important Uses
  • Convex Lens → Magnifying glass, camera, microscope.
  • Concave Lens → Used to correct myopia (short-sightedness).

Quick Revision

  • Convex → Converging Lens
  • Concave → Diverging Lens

Human Eye

The human eye is a natural optical instrument that helps us see objects. The retina forms the image, while the optic nerve carries visual information to the brain.

Defect Corrected By
Myopia (Short-sightedness) Concave Lens
Hypermetropia (Long-sightedness) Convex Lens
Presbyopia Bifocal Lens
⭐ Important Facts
  • The retina is the light-sensitive part of the eye.
  • The iris controls the amount of light entering the eye.
  • The pupil is the opening through which light enters the eye.

📘 Remember

Myopia → Concave Lens

Hypermetropia → Convex Lens

Presbyopia → Bifocal Lens

Quick Revision

  • Retina → Image Formation
  • Iris → Controls Light
  • Myopia → Concave Lens
  • Hypermetropia → Convex Lens
📝 Frequently Asked Facts
  • Speed of Light = 3 × 10⁸ m/s
  • Speed of Sound in Air ≈ 343 m/s
  • Concave Mirror → Headlights
  • Convex Mirror → Rear-view Mirror
  • Myopia → Concave Lens
  • Hypermetropia → Convex Lens

Electricity

Electricity is the flow of electric charge through a conductor. It is one of the most important forms of energy and is widely used in homes, industries, transportation and communication.

🎯 Exam Focus Questions are commonly asked about electric current, voltage, resistance, Ohm’s Law and SI units.
Quantity SI Unit Symbol
Electric Current Ampere A
Voltage Volt V
Resistance Ohm Ω
Power Watt W

📘 Important Formulae

Current (I) = Charge ÷ Time

Power (P) = Voltage × Current

P = V × I
⭐ Important Facts
  • Electric current is measured using an Ammeter.
  • Voltage is measured using a Voltmeter.
  • Resistance opposes the flow of electric current.
  • Good conductors include copper, silver and aluminium.

Quick Revision

  • Current → Ampere
  • Voltage → Volt
  • Resistance → Ohm
  • Power → Watt

Ohm’s Law

Ohm’s Law states that the electric current flowing through a conductor is directly proportional to the potential difference across it, provided the temperature remains constant.

📘 Formula

V = I × R
⭐ Important Facts
  • Proposed by Georg Simon Ohm.
  • Resistance is measured in Ohms (Ω).
  • Used in electrical circuit calculations.

Magnetism

Magnetism is the property of certain materials to attract iron, nickel and cobalt. Every magnet has two poles—North Pole and South Pole.

Property Description
Like Poles Repel each other.
Unlike Poles Attract each other.
Natural Magnet Lodestone.
Artificial Magnet Bar Magnet, Horseshoe Magnet.
⭐ Important Facts
  • A freely suspended magnet always points in the north-south direction.
  • The Earth behaves like a giant magnet.
  • Electromagnets are widely used in electric bells and cranes.

Quick Revision

  • Like Poles → Repel
  • Unlike Poles → Attract
  • Natural Magnet → Lodestone

Modern Physics

Modern Physics deals with atoms, nuclei, radioactivity, X-rays, lasers and the photoelectric effect. Many questions in competitive exams are based on important discoveries and scientists.

Scientist Contribution
Albert Einstein Photoelectric Effect and Theory of Relativity.
J. J. Thomson Discovery of the Electron.
Ernest Rutherford Discovery of the Atomic Nucleus.
James Chadwick Discovery of the Neutron.
Niels Bohr Bohr’s Atomic Model.
⭐ Important Facts
  • X-rays were discovered by Wilhelm Conrad Röntgen.
  • Radioactivity was discovered by Henri Becquerel.
  • Marie Curie received Nobel Prizes for her work on radioactivity.

Important Scientists & Discoveries

Scientist Discovery / Law
Isaac Newton Laws of Motion & Universal Gravitation.
Galileo Galilei Studies on Motion.
Archimedes Principle of Buoyancy.
Blaise Pascal Pressure.
Michael Faraday Electromagnetic Induction.
Thomas Edison Practical Electric Lamp.
Alexander Graham Bell Telephone.

Important Physics Formulae

Speed = Distance ÷ Time

Velocity = Displacement ÷ Time

Acceleration = Change in Velocity ÷ Time

Force = Mass × Acceleration

Work = Force × Distance

Power = Work ÷ Time

Weight = Mass × Gravity

Pressure = Force ÷ Area

Current = Charge ÷ Time

Power = Voltage × Current

Ohm’s Law → V = I × R

📌 One-Minute Revision

  • ✔ SI Unit of Force → Newton (N)
  • ✔ SI Unit of Work & Energy → Joule (J)
  • ✔ SI Unit of Power → Watt (W)
  • ✔ SI Unit of Pressure → Pascal (Pa)
  • ✔ SI Unit of Electric Current → Ampere (A)
  • ✔ Speed = Distance ÷ Time
  • ✔ Force = Mass × Acceleration
  • ✔ Weight = Mass × Gravity
  • ✔ Sound cannot travel in vacuum.
  • ✔ Light travels fastest in vacuum.
  • ✔ Concave Mirror → Headlights
  • ✔ Convex Mirror → Rear-view Mirror
  • ✔ Myopia → Concave Lens
  • ✔ Hypermetropia → Convex Lens
  • ✔ V = I × R (Ohm’s Law)

Conclusion

Physics is one of the most important subjects in General Science for SSC, Railway, Banking, Defence, Police and State Government examinations. Topics such as Motion, Force, Work, Energy, Heat, Sound, Light, Electricity and Magnetism are regularly asked in competitive exams.

Revise important concepts, SI units, formulae, scientists and practical applications regularly. Consistent revision along with topic-wise MCQ practice will improve both conceptual understanding and examination performance.

These Physics Notes are designed to provide simple, exam-oriented study material for beginners as well as competitive exam aspirants. Save this page for quick revision and continue your preparation with regular practice.