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
