PHYSICS: OPTICS IN EVERYDAY LIFE

PHYSICS: OPTICS IN EVERYDAY LIFE

Hi Friends

Come On Let us dive into the ocean of General Science,

Working of the Human Eye

• Light entering the eye passes through the cornea and the pupil
• Then, the lens focuses light onto an array of photoreceptor cells in the back of the eye, called the retina
• There are two types of photoreceptor cells:
  • Rod cells: they are responsible for black and white vision, night vision and peripheral vision. They are more in number
  • Cone cells: they are responsible for colour vision. They are less numerous in number

Keywords: ias, upsc, civil service, study material, general studies

Defects in vision

• Presbyopia: as people age, the lens becomes less flexible and near point recedes from the eye. As a result objects far away cannot be see. Can be corrected using a converging lens
• Hyperopia: lens cannot decrease focal length to focus on nearby objects and so nearby objects cannot be see. Corrected using a converging lens
• Myopia: lens cannotincrease focal length to  focus on far away objects and so farther objects cannot be seen. Corrected using a diverging lens
• Astigmatism: occurs when the cornea is not spherical but instead elongated. Results in distorted images. Corrected using a cylindrical surface lens

Keywords: ias, upsc, civil service, study material, general studies

Applications of Mirrors

• Kaleidoscope: A toy in which multiple images are formed by two mirrors placed inside a tube
• Periscope: Two plane mirrors fixed facing each other  45 degrees. Used in submarines
• Concave mirror: When used close to face gives magnified image. Used for shaving, personal care etc
• Convex mirror: Produces smaller image but gives wider range of view. Used in rear view mirrors
• Parabolic mirror: A concave mirror whose section is the shape of a parabola, helps in focusing. Used as reflectors in search lights, car head lights etc

Keywords: ias, upsc, civil service, study material, general studies

Optical instruments and their applications

Instrument	Working principle	Applications
Microscope	Convex lens (converging lens) system consisting of very short focal length eyepiece and longer focal length objective	Magnifying tiny objects: molecular studies
Telescope	Convex lens system that provides regular magnification	Magnifying distant objects: astronomy
Binocular	Pair of telescopes mounted side-by-side	General use
Interferometer	Superposition of waves	To study interference properties of light
Photometer	Uses a light sensitive element (like photomultiplier) to measure light intensity	Used to measure reflection, scattering, fluorescence etc
Polarimeter	Light from a source passing through a polarizer and then measured	Measures dispersion or rotation of polarized light
Spectrometer	Works by measuring light intensity	Used to measure light properties: astronomy
Autocollimator	Projects and image onto a target mirror and measures deflection of returned image	Component alignment, measure deflection in optomechanical systems

Keywords: ias, upsc, civil service, study material, general studies

Optics in the atmosphere

Observed effect	Underlying cause	Description
Blue colour of sky	Rayleigh scattering	Higher frequencies (blue light) get more scattered than lower frequencies
Red colour of sunrise and sunset	Mei scattering	Scattering due to suspended particles (like dust) when sun’s rays have to travel longer distance
Halos/afterglows	Scattering	Scattering off ice particles
Sundog	Scattering	Scattering off ice crystals causing bright spots on the sky
Mirage	Refraction
Novaya Zemlya effect	Refraction	Sun appears to rise earlier than predicted
Fata Morgana	Refraction due to temperature inversion	Objects beyond the horizon can be seen elevated
Rainbow	Total internal reflection

Keywords: ias, upsc, civil service, study material, general studies

Optics for photography

Desired effect	Approach
Close up	Use macro lens
Long shot	Telephoto lens
Panoramic pictures	Wide angle lens
Handle low light conditions	Increase exposure time (decrease shutter speed)
Fast moving objects	Decrease exposure speed (increase shutter speed)
Increase depth of field (foreground and background both in focus)	Increase aperture i.e. f-number

Keywords: ias, upsc, civil service, study material, general studies

Optical Fibres

• Optical fibres are glass or plastic fibre that carries light
• Advantages include
  • low signal loss
  • immunity from electromagnetic interference
  • higher bandwidth (data rate)
  • low power consumption
• Optical fibres work on the principle of Total Internal Reflection
• Applications include long distance communication, endoscopy, light decorations etc

THANKS


JOHAR