KERALA PSC / PHYSICS / LIGHT / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY / NOTES

 

KERALA PSC / PHYSICS / LIGHT / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY / NOTES

KERALA PSC / PHYSICS / LIGHT / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY / NOTES

·      ‘The Corpuscular theory’ related to light was proposed by Issac Newton in 1675.

·      Study of light is known as optics

·      Light is an electromagnetic radiation

·      Through vacuum electromagnetic waves travels with a speed of 2.9979 × 10⁸ m/s

·      Paper, cardboard and stone are examples for opaque substances (substance which do not passes light)

·      Substances which allow the light to pass through are called transparent substances. Eg: glass

·      The particle which is supposed to travel faster than light is tachyon

·      Tachyons were discovered by E.C.G Sudarshan.

·      On a rainy afternoon a rainbow is seen in the east

·      A rainbow is always seen in the opposite direction of the sun

·      Rainbow is caused by reflection, refraction and dispersion of light by the water particles present in the atmosphere.

·      LASER is Light Amplification by Stimulated Emission of Radiation.

·      Laser is the surface intense radiation

·      LASER is a source of intense monochromatic light in the ultraviolet, visible or infrared region of the spectrum

·      LASER beams are used in the medical field to perform minute operations

·      LASER was discovered by Theodore Maiman in 1960

·      Visible spectrum is the band of colours obtained when a ray of light passes through a prism

·      Spectrum consists of seven colours viz., Violet, Indigo, Blue, Green, Yellow, Orange and Red (VIBGYOR)

·      Violet light is scattered most, blue somewhat less, and green, yellow and orange still less, in that order.

·      The reddish colour of the sun at the time of rise and set is due to scattering of light by tiny particles in the atmosphere.

·      Mirage is an optical illusion which is observed usually in deserts on hot summer days. ‘Land heating’ contributes in the formation of a mirage.

·      Principle of optical fibre is total internal reflection.

·      The phenomenon of emission of light in the visible region after absorbing certain electromagnetic radiations is called photoluminescence

·      Substances which show photoluminescence are called phosphors. Eg: Zinc silicate, Cadmium borate etc…

·       Red light is scattered least

·      The beautiful colour of the soap foam and oil spread water is due to interference of light

·      Red, green and blue are the primary colors.

·      Colour of an object depends on the colour of light falling on it and the colour it reflects

·      The branch of physics which deals with the measurement of light emitted by objects is called photometry.

·      In spectrometer, astronomical telescope is used.

·      There is no atmosphere on moon, hence in the absence of scattering of light, the sky appears white.

·      Astronomical telescope is used to observe heavenly bodies like moons, stars etc…

·      Green objects placed in red light will appear black.

·      A red cloth absorbs all the light except red. Thus, when green light falls upon a red cloth it absorbs the green light and has nothing to reflect and thus appears black. In science red, green and blue are called primary colours, they give other colour when suitably mixed the main secondary colours are yellow, cyan (pea-cock blue) and magenta.

When mixing:

          Red + Green = Yellow

          Red + Blue = Magenta

          Green + Blue = Cyan

          Red + Green + Blue = White

Reflection of light: When a ray of light strikes on a smooth surface and returns to the same medium, it is called reflection of light

·      Reflecting Surface is plane it is called plane mirror used in Perioscope. Two plane mirrors fixed falling one another at an angle 45⁰

·      The reflection of light takes place from a spherical surface are called spherical mirror they are two types Concave mirror and Convex mirror.

·      Concave mirror whose reflecting surface is curved inward concave mirror can be used for (1) for shaving as shaving mirror (2) As a reflector to concentrate light in solar cooker (3) As a reflector in astronomical telescope (4) in search light of automobiles (5) Opthalmoscope to examine throat and ear.

·      Convex Mirror: A spherical mirror whose reflecting surface is curved outward, convex mirror can be used for (1) As a rear view mirror in automobiles (2) As a device to check theft in shops (3) Bring views of corners which are not directly accessible.

·      In the spectrum violet light has short wave length and high frequency. While red light has the highest wave length and the least frequency.

·      A diamond sparkles due to total internal reflection because it has a high refractive index

·      MASER is Microwave Amplification by Stimulated Emission of Radiation. It was discovered by Charles H. Towns

·      Refraction is the sudden change of direction of light when passing from one transparent substance to another. When we put a stick in water it seems to be blended. It is due to refraction.

·      Interference: When two light waves cross through the same spot they interfere with each other, it may be constructive or destructive. Useful application of interference is in non-reflecting coating for glass.

·      Total internal Reflection: Let light is going from a denser to rarer medium if the angle of incidence is greater than the critical angle of incidence. No light is refracted into the second medium, total internal reflection cause diamond to sparkle, air bubbles in the water to glitter.

·      Mirage: A mirage is caused by the total internal reflection of light at layers of air of different densities.

·      Optical fibres: Uses the principle of total internal reflection for carrying pulses of light from a laser which represents the information such as computer data, telephonic conversations, television pictures, an optical fibre has much greater information carrying capacity than a copper cable.

·      Tyndall effect – the phenomenon of scattering light by colloidal particle.

·      Refraction of light finds its most useful application in lens, it is any transparent piece of material having at least one of which is curved. Two commonly used lens are concave lens and convex lens.

·      Human eye lens is a crystalline convex lens having flexible focal length.

·      Diffraction is the spreading out of waves of light as it passes through a narrow aperture. The spreading of light rays towards the screen from a projector in film theatre is due to diffraction.

·      Dispersion is the splitting up of light ray into different colours. Rainbow is formed due to dispersion. The seven colours of light has different wavelength. Hence when light passes through a prism each colour gets refracted at different angles.

·      A bubble of water shines because of total internal reflection

·      Refraction of light through air having very large temperature gradients causes a mirage

·      A periscope is a device which works by the principle of reflection and refraction.

·      When there is thunder we see the lightning first and hear the thunder later because the velocity of light is greater than the velocity of sound

·      When light is incident on the surface of an object some of light is bounced back into the same medium. This is known as phenomenon of reflection.

·      More reflection and less scattering of light occurs from moist objects. This leads to brighter appearance of the coloured bodies.

·      The term light year is a unit employed in measuring distance.

·      The rays which appears to originate outside the earth: The cosmic rays

·      In a Doctor’s stethoscope the sound is intensified because of reflection of sound

·      Light from the sun reaches the earth in 8 minutes

·      Light travels fastest through vacuum. Through vacuum light travels with a speed of 3 ×10⁸m/s

·      The shortest distance for clear vision is 25 cm

·      Myopia or short sightedness is such a type of defect in which one can see nearby objects clearly but is difficult to see objects at long distances. Here image of the substance falls in front of the retina.

·      Myopia can be corrected by using a concave lens.

·      Hypermetropia or long sightedness is such a type of defect in which one can see distant objects clearly whereas nearby objects look blurred. Here the image of the substance falls behind the retina.

·      Hypermetropia can be corrected by using a convex lens of appropriate focal length.

·      Persons suffering from both myopia and hypermetropia use bifocal lenses to withstand the condition.

·      Astigmatism: This defect is due to the cornea not being spherical. This defect can be corrected by using a cylindrical lens, instead of a spherical lens.

·      As the age advances, the elasticity of eye becomes very much reduced. As a result, the near point of eye recedes gradually resulting in presbyopia. It can be corrected by convex glasses.

·      When we observe distant objects, the focal length of the eye lens increases and if we observe the objects nearby, the focal length of eye lens decreases.

·      Twenty – Twenty means perfect vision

·      The mage formed on the retina of the human eye is real and inverted

·      The lens in the human eye in convex

·      Pigments are substances used to colour paints, filters, plastics and other materials.

·      The sky generally looks blue because the blue colour of short wave length is scattered more than the longer waves of red light.

·      It is true that the violet waves are dispersed, even more than the blue. However, the sky does not appear violet because the sunlight is relatively weak in violet light.

·      The formation of brilliant colours in soap film is a consequence of the phenomenon of multiple refraction and interference.

·      An astronaut on an earth satellite will observe the sky as Black

·      The shortest height of a plane mirror required to show the full size image of a person of height ‘L’ cm is L / 2 cm

·      Diopter is the unit of power of lenses

·      Concave mirror is used as a burning glass

·      For the rear view, motorists use convex mirror

·      To concentrate light on the teeth, the dentists use concave mirrors

·      Film is a part of the camera which is analogous to the retina in the human eye.

     

KERALA PSC / PHYSICS / LIGHT / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY / NOTES