Sunday, July 4, 2010

APPSC GENERAL SCIENCE

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-n

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