Physics — Static GK for Competitive Exams

Why This Chapter Matters

Physics questions in SSC GD and RPF Constable exams are almost never numerical — they test static general knowledge: units, scientists, laws, and everyday physics facts. A constable candidate does not need to solve equations, but does need to instantly recall who discovered what, what unit measures which quantity, and basic definitions. This chapter is built entirely around that recall-based format.

Branches of Physics

Branch	What It Studies
Mechanics	Motion of objects and the forces causing it
Thermodynamics	Heat, temperature, and energy transfer
Optics	Behaviour of light
Electromagnetism	Electricity, magnetism, and their interrelation
Acoustics	Sound and its properties
Nuclear Physics	Structure and behaviour of atomic nuclei
Quantum Mechanics	Behaviour of matter and energy at atomic and subatomic scales
Astrophysics	Physical nature of stars, planets, and other celestial bodies

Fundamental and Derived Units (SI System)

The International System of Units (SI), adopted globally for scientific consistency, defines seven base (fundamental) quantities, from which all other physical quantities are derived.

Quantity	SI Unit	Symbol
Length	Metre	m
Mass	Kilogram	kg
Time	Second	s
Electric Current	Ampere	A
Temperature	Kelvin	K
Amount of Substance	Mole	mol
Luminous Intensity	Candela	cd

Common Derived Units

Quantity	SI Unit	Notes
Force	Newton (N)	Named after Sir Isaac Newton; 1 N = 1 kg⋅m/s²
Work/Energy	Joule (J)	Named after James Prescott Joule
Power	Watt (W)	Named after James Watt; 1 W = 1 J/s
Pressure	Pascal (Pa)	Named after Blaise Pascal
Frequency	Hertz (Hz)	Named after Heinrich Hertz
Electric Charge	Coulomb (C)	Named after Charles-Augustin de Coulomb
Electric Potential	Volt (V)	Named after Alessandro Volta
Electric Resistance	Ohm (Ω)	Named after Georg Simon Ohm
Magnetic Field Strength	Tesla (T)	Named after Nikola Tesla
Radioactivity	Becquerel (Bq)	Named after Henri Becquerel

Laws of Motion (Newton's Laws)

Sir Isaac Newton formulated three laws of motion in his work "Philosophiae Naturalis Principia Mathematica" (1687), which remain the foundation of classical mechanics.

Law	Statement	Common Example
First Law (Law of Inertia)	An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted upon by an external force	A passenger jerks forward when a bus suddenly brakes
Second Law	The rate of change of momentum of an object is directly proportional to the applied force and occurs in the direction of the force (F = ma)	A heavier object requires more force to achieve the same acceleration
Third Law	For every action, there is an equal and opposite reaction	A rocket launches upward as gases are expelled downward

Inertia is the tendency of an object to resist a change in its state of motion; it is directly related to an object's mass — the greater the mass, the greater the inertia.

Important Physical Quantities and Their Nature

Quantity	Scalar or Vector	Notes
Distance	Scalar	Total path length travelled
Displacement	Vector	Shortest straight-line distance between start and end points, with direction
Speed	Scalar	Distance covered per unit time
Velocity	Vector	Displacement per unit time
Mass	Scalar	Amount of matter in an object; remains constant everywhere
Weight	Vector	Force exerted by gravity on mass; varies with location (W = mg)
Force	Vector	Push or pull that changes the state of motion of an object
Work	Scalar	Product of force and displacement in the direction of force
Energy	Scalar	Capacity to do work
Momentum	Vector	Product of mass and velocity

Forms of Energy

Energy exists in several interconvertible forms, and the Law of Conservation of Energy states that energy can neither be created nor destroyed, only transformed from one form to another. Kinetic energy is the energy possessed by a body due to its motion, while potential energy is the energy possessed due to position or configuration, such as an object held at a height. A pendulum at its highest point has maximum potential energy and zero kinetic energy, and the reverse is true at its lowest point.

Heat and Temperature

Term/Scale	Details
Celsius Scale	Water freezes at 0°C and boils at 100°C at standard atmospheric pressure
Fahrenheit Scale	Water freezes at 32°F and boils at 212°F
Kelvin Scale	The SI unit of temperature; 0 K (absolute zero) is the theoretical point of no molecular motion, equal to -273.15°C
Conduction	Transfer of heat through direct contact, common in solids
Convection	Transfer of heat through the movement of fluid (liquid or gas) particles
Radiation	Transfer of heat through electromagnetic waves, requiring no medium; how the Sun's heat reaches Earth

Light and Optics — Static Facts

• The speed of light in a vacuum is approximately 3 x 10⁸ metres per second (about 300,000 km/s), the fastest speed possible according to physics as currently understood.
• Light travels fastest in a vacuum and slowest in denser mediums like glass or water — this is why light bends (refracts) when passing between mediums of different densities.
• A concave mirror converges light rays and is used in torches, headlights, and shaving mirrors; a convex mirror diverges light rays and is used in vehicle rear-view mirrors for a wider field of view.
• A convex lens converges light and is used to correct long-sightedness (hypermetropia); a concave lens diverges light and is used to correct short-sightedness (myopia).
• The scattering of sunlight by particles in the atmosphere, more strongly at shorter wavelengths, explains why the sky appears blue — a phenomenon known as Rayleigh scattering.
• A rainbow forms due to the refraction, dispersion, and internal reflection of sunlight in water droplets, splitting white light into its seven constituent colours (VIBGYOR: Violet, Indigo, Blue, Green, Yellow, Orange, Red).
• The human eye focuses light using the lens onto the retina; the nearest point of clear vision for a normal eye is roughly 25 cm.

Sound — Static Facts

• Sound is a mechanical wave and requires a medium to travel — it cannot travel through a vacuum, unlike light.
• Sound travels fastest in solids, slower in liquids, and slowest in gases, because particles are more closely packed in solids.
• The speed of sound in air at room temperature is approximately 343 metres per second.
• The unit of loudness (sound intensity level) is the decibel (dB).
• Frequencies above 20,000 Hz are called ultrasonic (ultrasound), used in medical imaging and SONAR; frequencies below 20 Hz are called infrasonic.
• The normal human hearing range is approximately 20 Hz to 20,000 Hz.
• An echo is the reflection of sound waves off a surface, perceived distinctly if the reflected sound arrives at least about 0.1 seconds after the original.

Electricity and Magnetism — Static Facts

• Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across it, at constant temperature (V = IR).
• A conductor allows electricity to pass through easily (e.g., copper, silver, aluminium); an insulator resists the flow of electricity (e.g., rubber, glass, wood).
• Silver is the best conductor of electricity, followed closely by copper, which is more commonly used commercially due to cost.
• A fuse is a safety device containing a wire that melts and breaks the circuit when current exceeds a safe limit, protecting appliances from damage.
• An electric generator converts mechanical energy into electrical energy, based on the principle of electromagnetic induction discovered by Michael Faraday.
• An electric motor converts electrical energy into mechanical energy, working on the reverse principle of a generator.
• A transformer changes the voltage of alternating current (AC) and cannot work with direct current (DC).
• Every magnet has two poles, north and south; like poles repel each other, and unlike poles attract.
• The Earth itself behaves like a giant magnet, with its magnetic north pole located near the geographic South Pole (and vice versa), which is why the north-seeking end of a compass needle points toward the Earth's geographic North.

Famous Scientists and Their Discoveries/Laws

Scientist	Discovery/Contribution
Sir Isaac Newton	Laws of motion, universal law of gravitation
Albert Einstein	Theory of relativity; E = mc² (mass-energy equivalence); Nobel Prize for the photoelectric effect
Michael Faraday	Laws of electromagnetic induction
James Clerk Maxwell	Classical theory of electromagnetic radiation, unifying electricity, magnetism, and light
Galileo Galilei	Pioneered the use of the telescope for astronomy; laws of falling bodies
Archimedes	Principle of buoyancy (Archimedes' Principle) and the law of the lever
Blaise Pascal	Pascal's Law of fluid pressure
Georg Simon Ohm	Ohm's Law of electrical resistance
Marie Curie	Pioneering research on radioactivity; discovered polonium and radium; only person to win Nobel Prizes in two different sciences
Ernest Rutherford	Discovered the atomic nucleus through the gold foil experiment
J. J. Thomson	Discovered the electron
James Chadwick	Discovered the neutron
Nikola Tesla	Pioneering work on alternating current (AC) electrical systems
C. V. Raman	Discovered the Raman Effect (scattering of light), earning India's first Nobel Prize in science, 1930
S. Chandrasekhar	Chandrasekhar Limit, related to the evolution and collapse of stars; Nobel Prize in Physics, 1983
Homi J. Bhabha	Father of the Indian nuclear programme

Gravitation and Motion — Additional Static Facts

• Newton's Law of Universal Gravitation states that every object in the universe attracts every other object with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
• The acceleration due to gravity on Earth's surface is approximately 9.8 metres per second squared, usually denoted "g."
• Weight varies with location because it depends on local gravitational pull, while mass remains the same everywhere in the universe — an astronaut has the same mass on the Moon as on Earth, but weighs less on the Moon because lunar gravity is about one-sixth of Earth's.
• A body in free fall experiences weightlessness because both the body and its surroundings accelerate at the same rate, cancelling the sensation of weight, as experienced by astronauts in orbit.
• Centripetal force is the force directed toward the centre of a circular path that keeps an object moving in that circle, essential to satellite motion and objects being swung on a string.
• The Law of Conservation of Momentum states that the total momentum of a closed system remains constant unless acted upon by an external force, applicable in collisions.

Archimedes' Principle and Buoyancy

Archimedes' Principle states that a body submerged (fully or partially) in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces. This explains why objects float or sink: an object floats if its density is less than the density of the fluid, and sinks if its density is greater. This is why a ship made of steel, which is denser than water, can still float — its overall shape displaces enough water to generate sufficient buoyant force.

Common Physics Instruments and What They Measure

Instrument	Measures
Barometer	Atmospheric pressure
Thermometer	Temperature
Ammeter	Electric current
Voltmeter	Electric potential difference (voltage)
Galvanometer	Small electric currents
Hygrometer	Humidity
Anemometer	Wind speed
Seismograph	Intensity of earthquakes
Odometer	Distance travelled by a vehicle
Tachometer	Rotational speed of an engine or shaft
Lactometer	Purity of milk (based on density)
Sphygmomanometer	Blood pressure
Spectrometer	Properties of light over a specific portion of the electromagnetic spectrum

Everyday Physics — Common GK Application Facts

• A thermos flask keeps liquids hot or cold by minimising heat transfer through conduction, convection, and radiation using a vacuum layer and reflective walls.
• Pressure cookers cook food faster because increased pressure raises the boiling point of water above 100°C, allowing food to cook at a higher temperature.
• Ice floats on water because water expands and becomes less dense upon freezing, an unusual property compared to most substances, which contract when they solidify.
• A ball bounces due to the elastic nature of its material, converting kinetic energy into potential energy on impact and back again.
• Friction is a force that opposes relative motion between surfaces in contact; it is necessary for walking, driving, and writing, but reduces mechanical efficiency in machines.
• Lubricants like oil and grease reduce friction between moving mechanical parts.
• A satellite stays in orbit because gravitational pull provides the exact centripetal force needed to keep it moving in a curved path around Earth rather than flying off in a straight line.
• Radioactivity was discovered by Henri Becquerel in 1896, and further studied extensively by Marie and Pierre Curie.

Simple Machines

A simple machine is a basic mechanical device that changes the direction or magnitude of a force, making work easier, even though it does not reduce the total amount of work done (ignoring friction losses). SSC-level questions typically ask which everyday tool corresponds to which simple machine.

Simple Machine	Examples
Lever	See-saw, crowbar, scissors, bottle opener
Wheel and Axle	Doorknob, steering wheel, bicycle wheel
Pulley	Well/bucket system, flagpole, cranes
Inclined Plane	Ramp, staircase, sloped road
Wedge	Axe, knife, chisel
Screw	Bolts, jar lids, drill bits

Levers are further classified into three classes based on the relative positions of the fulcrum, effort, and load: a first-class lever has the fulcrum between effort and load (e.g., a see-saw); a second-class lever has the load between the fulcrum and effort (e.g., a wheelbarrow); and a third-class lever has the effort between the fulcrum and load (e.g., a pair of tongs or a human forearm lifting a weight).

Famous Inventions and Inventors

Invention	Inventor
Telephone	Alexander Graham Bell (1876)
Light Bulb (practical, long-lasting filament)	Thomas Alva Edison
Steam Engine (improved/practical version)	James Watt
Television	John Logie Baird
Radio	Guglielmo Marconi (credited with the first practical long-distance radio transmission)
Dynamite	Alfred Nobel
Airplane	Wright Brothers (Orville and Wilbur Wright), 1903
World Wide Web	Tim Berners-Lee
Laws of Gravity	Isaac Newton
X-rays	Wilhelm Conrad Rontgen

Key Facts at a Glance

• Newton's three laws of motion form the foundation of classical mechanics.
• SI base units: metre (length), kilogram (mass), second (time), ampere (current), kelvin (temperature), mole (amount of substance), candela (luminous intensity).
• The speed of light in vacuum is about 3 x 10⁸ m/s; sound cannot travel through a vacuum.
• Sound travels fastest in solids and slowest in gases; light travels fastest in a vacuum and slowest in denser media.
• Archimedes' Principle explains buoyancy and why objects float or sink.
• Ohm's Law relates voltage, current, and resistance (V = IR).
• C. V. Raman won India's first Nobel Prize in science (1930) for the Raman Effect.
• Ice is less dense than water, which is why it floats.
• A pressure cooker raises the boiling point of water to cook food faster.
• The human audible frequency range is approximately 20 Hz to 20,000 Hz.

Practice MCQs

1. Which law states that every action has an equal and opposite reaction?
   a) Newton's First Law b) Newton's Second Law c) Newton's Third Law d) Law of Conservation of Energy
   Answer: c) Newton's Third Law. This law explains phenomena like rocket propulsion.
2. What is the SI unit of electric resistance?
   a) Volt b) Ampere c) Ohm d) Watt
   Answer: c) Ohm. It is named after Georg Simon Ohm.
3. Which scientist is associated with the principle of buoyancy?
   a) Isaac Newton b) Archimedes c) Blaise Pascal d) Galileo Galilei
   Answer: b) Archimedes. His principle explains why objects float or sink in a fluid.
4. The speed of light in a vacuum is approximately:
   a) 3 x 10⁵ m/s b) 3 x 10⁶ m/s c) 3 x 10⁷ m/s d) 3 x 10⁸ m/s
   Answer: d) 3 x 10⁸ m/s. This is the fastest speed possible according to current physics.
5. In which medium does sound travel fastest?
   a) Vacuum b) Gas c) Liquid d) Solid
   Answer: d) Solid. Closely packed particles in solids transmit sound waves most efficiently.
6. Which Indian scientist won a Nobel Prize for the discovery of the Raman Effect?
   a) Homi Bhabha b) C. V. Raman c) S. Chandrasekhar d) Vikram Sarabhai
   Answer: b) C. V. Raman. He won it in 1930, India's first Nobel Prize in the sciences.
7. A convex lens is used to correct which vision defect?
   a) Myopia (short-sightedness) b) Hypermetropia (long-sightedness) c) Astigmatism d) Colour blindness
   Answer: b) Hypermetropia. A convex lens converges light rays to focus them correctly on the retina.
8. Which instrument is used to measure atmospheric pressure?
   a) Thermometer b) Hygrometer c) Barometer d) Anemometer
   Answer: c) Barometer. It is commonly used in weather forecasting.
9. Why does ice float on water?
   a) Ice is a different chemical compound b) Ice has lower density than water c) Ice contains trapped air only d) Water has higher surface tension
   Answer: b) Ice has lower density than water. Water is unusual in that it expands upon freezing.
10. What is the SI unit of power?
    a) Joule b) Newton c) Watt d) Pascal
    Answer: c) Watt. One watt equals one joule of energy per second.
11. Which of the following is a vector quantity?
    a) Mass b) Speed c) Work d) Velocity
    Answer: d) Velocity. Velocity has both magnitude and direction, unlike speed, mass, or work.
12. Who discovered the electron?
    a) Ernest Rutherford b) James Chadwick c) J. J. Thomson d) Niels Bohr
    Answer: c) J. J. Thomson. Rutherford later discovered the nucleus, and Chadwick discovered the neutron.