Light 7&8 Flashcards
Angle of deviation =
Diff btw angle of incidence light and angle of exiting ray
…………………lens helps to see things far away
Concave
What are the 2 types of photoreceptors
Rods and cone. Comes are more in no
…………. lens helps far sighted people ( who cannot see things close to them)
Convex
Mirror in which virtual img is magnified
Concave mirror
What is wave theory
The principal by Christian Huygens that light travels in the form of waves
Phase velocity =
Lambda/ time period
Speed of light in glass
2x10 raised to8
In a kaleidoscope,mirror tilted at an angle of
45 degree
Refractive index of water
1.33
No of times light is deflected in a prism
2
When does optical centre coincide with the geometrical centre
If the radii of 2 surfaces are equal
Img formed by eyes
Real and inverted
Refractive index of glass
1.5
Speed of light in water
2.25*10 raised to 8
Penumbra is seen outside the …………
Umbra
What are photoreceptors
The cells of retina that respond to light
Relation btw focal length and radius of curvature
2F=R
Eyes are ………… lens
Convex
Where is retina situated
Behind the eyes
Examples of translucent obj
Froasted or grounded glass,greased paper,paraffin wax
The white part of a eye
Sclera
Iris contains
Pupil
Pupil can
Contract and relax
Waves energy is directly proportional to
Amplitude sq
Intense inversely proportional to
radius sq (distance)
Shorter the wavelength of a wave
More the energy and viceversa
Objects after getting energy one way to emit it is in the form of
Light as it is a form of energy
Objects which are hotter emit waves with
Higher energy that means shorter wavelength
Even humans emit light but it is in the
Far infrared spectrum
Interference is just
Overlapping of two waves
Main 2 types of interference
Constructive interference
Destructive interference
In constructive interference the two waves join together to make the
Amplitude increased
In a destructive interference two waves -
Cancel each other’s effect
The electrons energy determines
where it revolves around the nucleus
Increase in electron energy results in increase in distance from
Nucleus
Above the nucleus theoretical there is a ladder
Where electrons are Situated
The more higher electrons are situated in a ladder the more
Energy
Electrons can go higher in the ladder if it gets
Energy
How does electrons get energy
Through light
If the electrons decide to come down to a lower step in the ladder
It emits light as it is a form of energy
But more energy shorter wavelength and this can determine the color of the light emitted.
In Different substances when an electron comes down in the ladder it emits different amounts of energy so
As based on amount of energy emitted by an electron, color of wave is determined by wavelength which is determined by the energy.
So different substances emit different colours
Basically as different substances emit different wavelengths (based on energy)of light when an electron goes down. This helps in understanding what celestial objects are made of based on the color they emit.
This is done by spectrometer which can precisely measure wavelength of light emitted by an object and thus make out what it is made of.
This helped us in understanding what planets many light yrs away are made of
Power of lens is
1/ focal length
Power of lens unit
Diopter
Mirror formula -
1/u+1/v=1/f
U - object distance
V - image distance
F - focal length
Magnification of an object is
Height of image / height of object
OR
Image distance / object distance
If the image is virtual - magnification - positive
If the image is real - magnification - negative
According to Huygens principle
Every point of a wave can be treated as a source of another wave that spreads out periodically
Planck’s constant
6.6 x 10*-34 Joule seconds (JS)
Optics is divided into three parts
Geometrical optics
Wave optics
Quantum optics
Geometrical optics also called
Ray optics
Deals with the refraction and reflection of light
Wave optics also called
Physical optics
Deals with NATURE of light and effects like diffraction,polarisation,interference etc.
Quantum optics ?
Deals with INTERACTION of light with atomic entities.
E.g. photo electric effect , atomic excitation
Particle nature of light is explained by
Newton’s corpuscular theory
Newton’s corpuscular theory
According to Newton , light travels in space as a stream of very small particles called corpuscles.
It failed to explain interference and diffraction of light.
Wave theory of light was published by
Christian Huygen
It failed to explain photo electric effect of light
Quantum theory of light was given by
Planck
Rest mass of photon is
0
3 theories about light
Corpuscular theory by Newton
Wave theory by Christian Huygens
Quantum theory by Planck
According to quantum theory
Both light and matter consists of tiny particles that have wavelike properties.
Only when particles are small enough, they show their wave properties
Light composed of particles called(energy packets)
Matter consists of electrons, protons,neutrons
Particles of light are very small , so exhibits wave like properties.
This quantum theory satisfies every property of light by saying light has a dual nature as a particle and a wave.
Visible light has a wavelength of
400-750 nm
White light ?
Light that contains all frequencies in the visible region.
Quantum mechanics
A mathematical model that describes the behaviour of particles on an atomic scale.
It tells that matter and energy are quantised ; they come in small discrete packets.
Photon definition
It is the quantum of electromagnetic radiation.
The term quantum is the smallest elemental unit of a quantity.
So one quantum of an electromagnetic radiation is called a photon.
Plural of quantum - quanta
Photo electric effect
When light strikes a metal it causes an electron to be ejected from it.
Energy of a photon in a wave of light
E = h x f
h - Planck’s constant
f - frequency
Total energy of the electromagnetic wave would be the sum of energy of all the photons
Energy of a photon is so small ; it is measured in
eV - electron volts
1 eV = 1.6 x 10* -19 Js
Who explained the nature of photo electric effect
Albert Einstein
Both real and virtual images can be
Photographed
Focal length of a plane mirror
Infinity
Power of a plane mirror is
0
Keeping the incident ray fixed ; if the mirror is rotated with an angle of “x” about an axis in the plane of mirror; the reflected ray is rotated through an angle of
“2x”
Deviation definition
Angle between the DIRECTIONS of the incident ray and emergent ray.
Angle of deviation = 180 - ( i + r ) = 180 - 2i
Reflection of light ………….. changes
Amplitude or intensity of light changes
A thick plane mirror
Forms multiple images , and out of this the second one is the brightest; after that the intensity of the image decreases.
No of images formed formed when object is placed between two mirrors
If -
A) 360/theta is even ; then -1
B) 360/theta is odd -
i) symmetric = -1
ii) asymmetric
C) 360/theta is a fraction then take the integer part
Focal plane
A plane passing through the principal focus at right angle to the principal axis.
A ray incident parallel to the principal axis (concave and convex mirrors)
Passes through the focus
A ray incident through the focus is reflected (concave and convex mirrors)
Parallel to the principal axis
