Science Facts : Optics – SARKARI LIBRARY

homogeneous

Homogeneous means having uniform composition or structure throughout. (e.g., salt in water).
- Homogeneous mixture ≠ heterogeneous mixture (heterogeneous is non‑uniform).
In maths/science, properties are the same at every point or part.
A homogeneous equation has all terms of the same degree.
A homogeneous polynomial has all terms of equal total degree.
A homogeneous catalyst is in the same phase as the reactants.
Homogeneous reaction occurs when all reactants are in the same phase.
Homogeneous solids have consistent structure and properties throughout.

energy

Energy is the capacity to do work.
The SI unit of energy is Joule (J).
Kinetic energy is the energy of a moving body.
Potential energy is stored energy due to position or configuration.
Mechanical energy = Kinetic energy + Potential energy.
Chemical energy is stored in chemical bonds.
Electrical energy comes from moving electric charges.
Thermal energy is due to the motion of particles in a substance.
Nuclear energy comes from the nucleus of an atom.
Renewable energy sources include solar, wind, hydro, and biomass.
Non-renewable energy sources include coal, oil, natural gas, and nuclear fuels.
Solar energy is harnessed from the Sun’s radiation.
Wind energy is obtained by converting wind motion into electricity.
Hydropower converts flowing water into electrical energy.
Energy cannot be created or destroyed, only transformed (Law of Conservation of Energy).
Power is the rate at which energy is used or transferred.
The SI unit of power is Watt (W).
1 calorie = energy required to raise 1g of water by 1°C.
1 kilowatt-hour (kWh) = 3.6 × 10⁶ Joules.

electromagnetic

Electromagnetic waves were first predicted by James Clerk Maxwell in 1864.
Heinrich Hertz first experimentally demonstrated EM waves in 1887.
Electromagnetic waves do not require a medium to propagate; they can travel in vacuum.
The speed of electromagnetic waves in vacuum is 3 × 10⁸ m/s.
EM waves consist of perpendicular electric and magnetic fields, oscillating in phase.
The direction of propagation of an EM wave is perpendicular to both electric and magnetic fields.
EM waves carry energy and momentum.
The electromagnetic spectrum includes: Radio, Microwave, Infrared, Visible light, Ultraviolet, X-rays, and Gamma rays.
Radio waves have the longest wavelength, gamma rays have the shortest.
EM waves follow the inverse square law, i.e., intensity decreases with square of distance.
EM waves are used in communication, radar, medical imaging, and satellite technology.
Light is an electromagnetic wave visible to human eyes.
Polarization occurs only in transverse EM waves.
EM waves in vacuum travel at constant speed, independent of frequency.

vacuum

Vacuum is a space completely devoid of matter, including air.
The term “vacuum” comes from the Latin word vacuus, meaning “empty.”
Perfect vacuum is theoretically impossible to achieve on Earth.
A vacuum has no air pressure, so liquids boil at lower temperatures.
Outer space is considered a near-perfect vacuum.
Vacuum is used in electronic devices like vacuum tubes and cathode ray tubes.
Vacuum pumps are devices that remove air and gases to create a vacuum.
In a vacuum, sound cannot travel because there is no medium.
Vacuum is essential for processes like freeze-drying, vacuum packing, and semiconductor manufacturing.
The concept of vacuum is fundamental in physics, including quantum mechanics and general relativity.

photoelectric effect

The photoelectric effect is the emission of electrons from a metal surface when light falls on it.
Observed by Heinrich Hertz in 1887.
Explained by Albert Einstein in 1905 using the concept of light quanta (photons).
Light must have frequency above a threshold value to emit electrons; below it, no emission occurs regardless of intensity.
Threshold frequency (ν₀): Minimum frequency of light needed to eject electrons from a metal.
Work function (Φ): Minimum energy required to remove an electron from the metal surface.
The kinetic energy of emitted electrons: (Einstein’s equation).
Photoelectric current depends on light intensity if frequency is above threshold.
Emission of electrons is instantaneous; no time lag observed.
Applications: Photoelectric cells, solar panels, light meters, automatic doors.
Demonstrated the particle nature of light, supporting the concept of photons.
Metals with lower work function emit electrons more easily.
Increasing the intensity of light increases the number of electrons, not their energy.

photon

Photon is a elementary particle and a quantum of light.
It is massless and has zero electric charge.
Photon always moves at the speed of light (c = 3 × 10⁸ m/s) in vacuum.
It exhibits dual nature: particle-like and wave-like behavior (wave-particle duality).
Photon carries energy (E = hν) and momentum (p = E/c).
Frequency (ν) of photon determines its energy.
Photon is the force carrier of the electromagnetic force.
Photons are bosons and obey Bose-Einstein statistics.
They have spin = 1, making them vector bosons.
Photons can interact with charged particles but do not interact with each other in normal conditions.
The concept of photon was introduced by Albert Einstein in 1905 to explain the photoelectric effect.
Applications: lasers, optical fibers, photosynthesis, solar cells, quantum communication.

Interference

Interference is a phenomenon of wave optics.
It occurs due to the superposition of two or more coherent waves.
- Coherent: Lasers (highly coherent), loudspeakers driven by the same signal.
  - Constant Phase Difference:
  - Same Frequency & Wavelength:
- Incoherent: Light from a flashlight or incandescent bulb (random photon emission).
The term interference was first explained by Thomas Young.
Interference results in redistribution of light intensity.
It produces alternate bright and dark fringes on the screen.
Constructive interference occurs when path difference = nλ.
Destructive interference occurs when path difference = (2n+1)λ/2.
The sources must be coherent to produce sustained interference.
Interference cannot be obtained from two independent light sources.
The fringe width depends on wavelength, distance of screen, and slit separation.
Interference pattern is independent of the nature of light source.
Maximum intensity occurs at bright fringes.
Minimum (zero) intensity occurs at dark fringes.
Interference is strong proof of the wave nature of light.
The most famous experiment on interference is Young’s Double Slit Experiment.
Interference is observed in light, sound, and water waves.
Fringe width increases with increase in wavelength.
Fringe width decreases with increase in slit separation.
Interference differs from diffraction in that two sources are involved.

Diffraction

Diffraction is the bending and spreading of waves around obstacles or through narrow openings.
Diffraction is a wave phenomenon and cannot be explained by particle nature alone.
Diffraction is significant when the size of the obstacle or aperture is comparable to the wavelength.
Light shows diffraction only when it passes through a very narrow slit.
Diffraction occurs with all types of waves such as light, sound, and water waves.
The phenomenon of diffraction violates the laws of geometrical optics.
Diffraction patterns consist of alternate bright and dark fringes.
The central maximum in diffraction is the brightest and widest fringe.
In single-slit diffraction, the central maximum is twice as wide as other maxima.
The intensity of diffraction fringes decreases away from the central maximum.
Diffraction is more prominent for longer wavelengths.
Red light diffracts more than blue light due to its larger wavelength.
Diffraction was experimentally studied in detail by Augustin-Jean Fresnel.
The bending of sound waves around corners is an example of diffraction of sound.
Diffraction explains why light spreads in a shadow region.
The diffraction pattern depends on the shape and size of the aperture.
The phenomenon of diffraction supports the wave theory of light.
Diffraction grating works on the principle of diffraction and interference.
A diffraction grating produces sharp and well-defined spectral lines.
Diffraction limits the resolving power of optical instruments.

Polarization

Polarization is the phenomenon of restricting the vibrations of light waves to a single plane.
Polarization proves that light is a transverse wave.
Only transverse waves can be polarized; longitudinal waves cannot.
Light waves vibrate perpendicular to the direction of propagation.
Natural light vibrates in all possible planes perpendicular to its direction.
Plane polarized light vibrates only in one plane.
Unpolarized light becomes polarized after passing through a polarizer.
Polaroid sheets are commonly used as polarizers.
Polarization by reflection occurs at a specific angle called Brewster’s angle.
At Brewster’s angle, reflected light is completely plane polarized.
Brewster’s law states: tan θ = μ, where μ is the refractive index.
Polarization by refraction occurs when light passes through a transparent medium.
Polarization by scattering explains the blue color of the sky.
Scattered light is partially polarized.
Polarization by selective absorption occurs in Polaroids.
Polarizing sunglasses reduce glare by blocking horizontally polarized light.
LCD screens work on the principle of polarization.
Polarization is used in photography to enhance contrast and reduce reflections.
Polaroids are made of long-chain molecules aligned in one direction.
Analyzer is a device used to detect the state of polarization of light.
When two polarizers are crossed at 90°, no light passes through.
Malus’ Law states: I = I₀ cos²θ.
Polarization is not observed in sound waves.
Sunlight is an example of unpolarized light.
Polarized light is used in stress analysis of materials.
Polarization is the phenomenon of restricting the vibrations of light waves to a single plane.
Only transverse waves can be polarized; longitudinal waves cannot.
Light waves are electromagnetic transverse waves, so they show polarization.
The direction of vibration of the electric field defines the plane of polarization.
Unpolarized light vibrates in all possible planes perpendicular to the direction of propagation.
Polarized light vibrates in only one plane.
Polarization proves the transverse nature of light.
Natural light from the sun is unpolarized.
Polarization can be produced by reflection, refraction, scattering, and absorption.
The angle at which reflected light becomes completely polarized is called Brewster’s angle.
At Brewster’s angle, the reflected and refracted rays are mutually perpendicular.
Brewster’s law: $μ=tan⁡ip\mu = \tan i_p$ , where $i_p$ is the polarizing angle.
Polaroid sheets are commonly used to produce plane-polarized light.
Polaroids work on the principle of selective absorption.
Malus’ law states that $I_0 \cos^2 \theta$ .
Polarization reduces glare from reflective surfaces like water and roads.
Sunglasses use polarization to reduce eye strain.
Scattering of light in the atmosphere causes partial polarization of skylight.
Double refraction (birefringence) occurs in anisotropic crystals like calcite.
Polarization is used in LCD screens, photography, and stress analysis.

Microscope

A microscope is an instrument used to view objects too small to be seen by the naked eye.
The term microscope comes from Greek words “mikros” (small) and “skopein” (to see).
The compound microscope was invented by Zacharias Janssen in 1590.
Antonie van Leeuwenhoek is known as the Father of Microscopy.
A compound microscope uses two lenses: objective lens and eyepiece lens.
The objective lens provides the primary magnification of the specimen.
The eyepiece lens further magnifies the image formed by the objective lens.
Total magnification = Objective lens magnification × Eyepiece magnification.
A simple microscope uses only a single convex lens.
A compound microscope can magnify objects up to 1000 times.
The resolution of a microscope is its ability to distinguish two close points as separate.
Resolution depends on the wavelength of light and numerical aperture.
A light microscope uses visible light to illuminate the specimen.
An electron microscope uses a beam of electrons instead of light.
The magnification power of an electron microscope is much higher than a light microscope.
Scanning Electron Microscope (SEM) provides 3D surface images.
Transmission Electron Microscope (TEM) provides internal structural details of specimens.
The stage is the platform where the slide is placed.
The diaphragm controls the amount of light passing through the specimen.
The mirror or illuminator provides light to observe the object clearly.
Immersion oil is used with high-power objectives to increase resolution.
A microscope is widely used in biology, medicine, forensic science, and material science.

Telescope

A telescope is an optical instrument used to observe distant objects in space.
The word telescope comes from Greek words “tele” (far) and “skopein” (to look).
The first practical telescope was invented in 1608 in the Netherlands.
Galileo Galilei was the first to use a telescope for astronomical observations.
Galileo used a telescope in 1609 to observe the Moon, Jupiter’s moons, and Saturn.
A telescope works by collecting and focusing light using lenses or mirrors.
Telescopes increase the apparent size and brightness of distant objects.
Refracting telescopes use lenses to focus light.
Reflecting telescopes use mirrors to focus light.
The first reflecting telescope was built by Isaac Newton in 1668.
Radio telescopes detect radio waves from space instead of visible light.
The largest optical telescopes are usually reflecting telescopes.
The light-gathering power of a telescope depends on the diameter of its aperture.
The resolving power of a telescope determines how clearly close objects can be distinguished.
Hubble Space Telescope is a famous space-based telescope launched in 1990.
Space telescopes avoid atmospheric distortion present on Earth.
Modern telescopes can observe objects billions of light-years away.
Telescopes are used in astronomy, astrophysics, and space research.
The mount of a telescope helps in tracking celestial objects.
Telescopes helped prove the heliocentric theory of the solar system.

Myopia

Myopia is also known as short-sightedness or near-sightedness.
In myopia, near objects are seen clearly but distant objects appear blurred.
Myopia occurs when the eyeball is too long or the eye lens is too powerful.
In myopia, the image of a distant object is formed in front of the retina.
Myopia is corrected by using a concave (diverging) lens.
The power of lens used to correct myopia is negative.
Myopia is a refractive error of the eye.
People with myopia have difficulty seeing distant road signs or blackboards.
Myopia usually develops during childhood or adolescence.
Excessive screen time and reading at close distance can increase the risk of myopia.
Myopia can be detected using a Snellen eye chart.
Myopia is commonly corrected with spectacles, contact lenses, or LASIK surgery.
In myopia, the far point of the eye is nearer than infinity.
Myopia is one of the most common vision defects worldwide.
Concave lenses used in myopia correction diverge light rays before they enter the eye.

Hypermetropia

Hypermetropia is also known as far-sightedness.
In hypermetropia, distant objects are seen clearly, but near objects appear blurred.
It occurs when the image is formed behind the retina.
The eyeball is shorter than normal in hypermetropia.
Hypermetropia can also occur if the eye lens has low converging power.
It is a type of refractive error of the eye.
A person with hypermetropia has difficulty in reading, writing, and near work.
Hypermetropia is corrected using a convex (converging) lens.
The convex lens helps by converging light rays before they enter the eye.
Hypermetropia is more common in elderly people.
Ciliary muscles are under constant strain in hypermetropia.
Headache and eye strain are common symptoms of hypermetropia.
Hypermetropia is opposite of myopia (near-sightedness).
In hypermetropia, the near point is farther than 25 cm.
The condition can be detected by an eye examination.
Hypermetropia may be present from birth.

Presbyopia

Presbyopia is an age-related defect of vision.
In presbyopia, a person has difficulty seeing nearby objects clearly.
It usually starts after the age of 40 years.
Presbyopia occurs due to loss of elasticity of the eye lens.
The ciliary muscles weaken with age, causing presbyopia.
It is a type of refractive error of the eye.
Presbyopia is not a disease, but a natural aging process.
Symptoms include eye strain, headache, and blurred near vision.
Presbyopia cannot be prevented completely.
It is corrected using convex (converging) lenses.
Reading glasses are commonly used to treat presbyopia.
Presbyopia may occur along with myopia or hypermetropia.
The near point of the eye shifts farther away in presbyopia.
Presbyopia affects both eyes equally.
It worsens gradually with increasing age.

Intensity

Intensity means the degree, level, or strength of something.
The word intensity comes from the Latin word “intensus”, meaning stretched or strained.
Intensity is commonly used to describe force, energy, or concentration.
In physics, intensity refers to power per unit area.
The SI unit of intensity is watt per square meter (W/m²).
Sound intensity depends on the amplitude of sound waves.
Light intensity determines how bright a source appears.
Earthquake intensity measures the effects and damage, not energy released.
Earthquake intensity is measured by the Modified Mercalli Intensity (MMI) Scale.
Richter scale measures earthquake magnitude, not intensity.
In psychology, intensity refers to the strength of emotions or feelings.
Exercise intensity shows how hard the body is working.
High intensity usually means greater impact or effectiveness.
Intensity is different from quantity; it shows quality, not amount.
In chemistry, reaction intensity depends on temperature and concentration.

concave

Concave means curved inward (like the inside of a bowl).
A concave lens is also called a diverging lens.
A concave mirror converges parallel rays to a focus.
The focal length of a concave mirror is negative (Cartesian sign convention).
A concave lens always forms a virtual, erect, and diminished image.
A concave mirror can form real or virtual images depending on object position.
The reflecting surface of a concave mirror is curved inward.
Concave shapes are common in mirrors, lenses, and utensils.
A concave polygon has at least one interior angle greater than 180°.
In daily life, a spoon’s inner surface behaves like a concave mirror.
Concave lenses are used to correct myopia (short-sightedness).
A concave mirror produces a magnified image when the object is placed between the pole and focus.
The center of curvature of a concave mirror lies in front of the mirror.
Concave is the opposite of convex.

convex

Convex means curved outward, like the outer surface of a sphere.
A convex lens converges parallel rays of light to a single point (focus).
A convex mirror always forms a virtual, erect, and diminished image.
Convex mirrors are also known as diverging mirrors.
The focal length of a convex mirror is always positive.
Convex mirrors provide a wide field of view.
Rear-view mirrors in vehicles are convex in shape.
In mathematics, a convex shape has all interior angles less than 180°.
A convex polygon has all diagonals lying inside the figure.
A set is called convex if the line segment joining any two points lies completely inside it.
Convex lenses are thicker at the center and thinner at the edges.
Convex lenses are used in magnifying glasses, cameras, and microscopes.
In economics, a convex curve shows increasing rate of change.
Convex mirrors reduce image size but increase safety.
The opposite of convex is concave.

reflection

Reflection is the bouncing back of light from a surface.
The surface from which light reflects is called a reflecting surface.
The ray of light that strikes the surface is called the incident ray.
The ray that bounces back after striking the surface is called the reflected ray.
The perpendicular drawn at the point of incidence is called the normal.
The angle between the incident ray and the normal is the angle of incidence.
The angle between the reflected ray and the normal is the angle of reflection.
First law of reflection: The incident ray, reflected ray, and the normal lie in the same plane.
Second law of reflection: The angle of incidence is equal to the angle of reflection.
Reflection follows the formula: ∠i = ∠r.
A plane mirror forms a virtual and erect image.
The image formed by a plane mirror is laterally inverted.
The distance of the object from the mirror is equal to the distance of the image behind the mirror.
The size of the image in a plane mirror is equal to the size of the object.
Regular reflection occurs from smooth surfaces.
Diffuse reflection occurs from rough surfaces.
Diffuse reflection does not violate the laws of reflection.
Reflection of light enables us to see objects.
A periscope works on the principle of reflection.
A kaleidoscope uses multiple reflections to form patterns.
Reflection occurs in mirrors, polished metals, and water surfaces.

Light

Light is a form of energy that enables us to see objects.
It exhibits dual nature: it behaves both as a wave (interference, diffraction) and as a particle (photoelectric effect, photon).
Light waves are electromagnetic waves and do not require a medium to travel (can travel in vacuum).
speed of light (c) in vacuum: 3 x 10⁸ m/s

Wave

A wave is a disturbance that transfers energy from one place to another without transferring matter.
Waves carry energy, not particles.
The point of maximum displacement in a wave is called crest.
The point of minimum displacement in a wave is called trough.
The distance between two consecutive crests or troughs is called wavelength.
The unit of wavelength is meter (m).
The number of waves passing a point per second is called frequency.
The SI unit of frequency is Hertz (Hz).
Time taken by a wave to complete one cycle is called time period.
Frequency is the inverse of time period.
Wave speed = frequency × wavelength.
The SI unit of wave speed is meter per second (m/s).
Mechanical waves require a medium to travel.
Sound waves are mechanical waves.
Electromagnetic waves do not require any medium.
Light waves are electromagnetic waves.
Waves in which particles vibrate perpendicular to the direction of propagation are called transverse waves.
Waves in which particles vibrate parallel to the direction of propagation are called longitudinal waves.
Sound waves are longitudinal in nature.
Water surface waves are transverse waves.
The maximum displacement of a particle from its mean position is called amplitude.
Greater amplitude means greater energy.
Echo is caused due to reflection of sound.
The phenomenon of bending of waves around obstacles is called diffraction.
Change in direction of a wave when it enters another medium is called refraction.
Superposition of two waves gives interference.
Doppler effect is the change in frequency due to relative motion between source and observer.
Human audible range is 20 Hz to 20,000 Hz.
Sound below 20 Hz is called infrasonic.
Sound above 20,000 Hz is called ultrasonic.
Ultrasonic waves are used in medical imaging and cleaning.

Dioptre

Dioptre is the unit of power of a lens.
It is denoted by the symbol D.
Power of a lens , where f is focal length in metres.
If focal length is 1 metre, power of lens is 1 dioptre.
Convex lens has positive power.
Concave lens has negative power.
Unit of dioptre is m⁻¹ (per metre).
Higher dioptre value means greater bending power of the lens.
Spectacle power is always measured in dioptres.
Dioptre is a derived SI unit (not a fundamental unit).
Power of lenses in contact is the algebraic sum of their powers.
A lens with focal length 0.5 m has power +2 D.
A lens with focal length –0.25 m has power –4 D.
Dioptre is commonly used in optics and eye testing.
It helps in determining vision defects like myopia and hypermetropia.

converge

Converge means to come together at one point.
Opposite of diverge.
Used for lines, paths, ideas, or trends coming together.
In geometry, lines converge when they meet at a point.
In geography, rivers converge when they join.
In economics, prices converge when differences reduce over time.
In science, light rays converge at the focal point of a lens.
In politics, parties may converge on common issues.
Convergence is the noun form of converge.
Commonly tested in synonyms & antonyms section.
Synonyms: meet, unite, merge, come together.
Antonyms: diverge, separate, split.
Example: All roads converge at the city center.

camera

A camera is an optical instrument that captures images, either as photographs or video.
The word camera comes from Latin camera obscura, meaning “dark chamber.”
A camera obscura is the earliest form of a camera, used long before modern photography.
The first permanent photograph was made by Joseph Nicéphore Niépce in 1826/27 using a camera obscura and bitumen on a plate.
Louis Daguerre developed the daguerreotype process in 1839, considered the first practical photographic process.
George Eastman founded Kodak in 1888, popularizing photography for the masses and introducing roll film.
The first digital camera was invented by engineer Steven Sasson at Kodak in 1975.
Modern digital cameras use image sensors (CCD or CMOS) to convert light into electronic signals.
DSLR stands for Digital Single Lens Reflex camera.
Mirrorless cameras lack the mirror system of a DSLR and offer a more compact design.
Mobile phone cameras have revolutionized photography, making cameras widely accessible.
Pixel count (megapixels) measures sensor resolution; higher doesn’t always mean better quality.
Aperture controls how much light enters the camera; represented as f-numbers (e.g., f/1.8, f/4).
Shutter speed determines how long the sensor is exposed to light.
ISO indicates the sensor’s light sensitivity; higher ISO increases brightness but also noise.
Optical zoom uses lens elements to magnify without quality loss; digital zoom crops the image.
Photography was officially recognised as an art form in many countries by the early 20th century.
A telephoto lens has a long focal length, useful for distant subjects.
A wide-angle lens captures wider scenes with short focal length.
Macro photography captures subjects at very close range.
Camera Obscura – Concept known since ancient Greece (~5th century BC).
First Photograph – 1826/27 (Niépce).
Daguerreotype – 1839 (Louis Daguerre).
Kodak Camera Roll – 1888 (George Eastman).
First Digital Camera – 1975 (Steven Sasson, Kodak).
Camera obscura means dark room.
CCD = Charge-Coupled Device; CMOS = Complementary Metal–Oxide–Semiconductor.
DSLR uses a reflex mirror; mirrorless does not.
Aperture, shutter speed, and ISO form the exposure triangle.
Optical zoom is better than digital zoom for quality.

diverge

The word “diverge” means to separate from a path, direction, or opinion.
In mathematics, diverge refers to a series or sequence that does not converge to a limit.
Synonyms: deviate, differ, separate, branch off.
Antonyms: converge, meet, unite.
Usage in a sentence: “The two roads diverge at the hilltop.”
In biology, species may diverge due to evolution, forming different traits.
Divergent thinking in psychology refers to generating multiple creative solutions to a problem.
The opposite of diverge in opinions is often to agree or converge in thought.

projector

A projector is an optical device used to project images or videos onto a surface, usually a screen or wall.
The first slide projector was invented in 1659 by Christiaan Huygens.
Digital projectors were introduced in the late 20th century, replacing traditional film projectors.
Projectors work on the principle of light projection and lens focusing.
Common types of projectors include LCD (Liquid Crystal Display), DLP (Digital Light Processing), and LED projectors.
DLP projectors use thousands of tiny mirrors to create images, developed by Texas Instruments in 1987.
LCD projectors split light into red, green, and blue components to display images.
Modern projectors can be portable, ceiling-mounted, or integrated into devices like laptops and smartphones.
Projectors are widely used in classrooms, offices, home theaters, and large events.
Laser projectors provide brighter and sharper images with longer lifespan compared to traditional lamps.
Some projectors support 3D projection for immersive visual experiences.
The contrast ratio and lumens are key specifications determining projector brightness and image quality.
Short-throw projectors can project large images from a short distance.
Smart projectors have inbuilt apps, Wi-Fi, and streaming capabilities.
The largest projector screen in the world measures over 1,000 square meters.

Magnification

Magnification refers to the process of enlarging the appearance of an object.
It is the ratio of the size of the image to the size of the object.
Formula: Magnification (M) = Image height (hᵢ) / Object height (hₒ) = – Image distance (v) / Object distance (u).
M > 1 → Image is magnified; M < 1 → Image is diminished.
Positive magnification (M > 0) → Image is upright.
Negative magnification (M < 0) → Image is inverted.
Magnifying glasses produce virtual, upright, and magnified images.
Microscopes and telescopes use multiple lenses to achieve high magnification.
Linear magnification refers to enlargement in one dimension; angular magnification refers to the apparent increase in angular size.
Magnification depends on focal length and object distance for lenses and mirrors.
No magnification occurs when object is at infinity or at the focus of lens/mirror.

refractive index

Refractive index is denoted by ‘n’.
It is defined as the ratio of speed of light in vacuum to speed of light in medium.
Formula: n = c / v, where c = speed of light in vacuum, v = speed in medium.
Refractive index is dimensionless (has no unit).
It determines how much light bends or refracts when entering a medium.
n > 1 for all transparent materials (except in exotic cases like negative index metamaterials).
Light bends towards the normal when passing from a medium with lower refractive index to higher.
Refractive index of water ≈ 1.33, glass ≈ 1.5, diamond ≈ 2.42.
Snell’s law uses refractive index: n₁ sinθ₁ = n₂ sinθ₂.
Refractive index is also related to wavelength; this phenomenon is called dispersion.
Higher refractive index implies slower light propagation in the medium.
Critical angle and total internal reflection are determined using refractive indices of two media.

Refraction

Refraction is the bending of light when it passes from one medium to another.
The change in speed of light causes refraction.
Refraction is measured by the refractive index of the medium.
The refractive index is the ratio of the speed of light in vacuum to that in the medium.
Light bends towards the normal when it enters a denser medium.
Light bends away from the normal when it enters a rarer medium.
Snell’s Law governs the refraction of light: n₁ sin θ₁ = n₂ sin θ₂.
Refraction is responsible for the apparent bending of a stick in water.
Lenses use refraction to converge or diverge light rays.
The human eye works on the principle of refraction.
Mirage is caused by the refraction of light in layers of air with different densities.
Total internal reflection occurs when light cannot refract and reflects completely inside a denser medium.