Blue lakes, ochre deserts, green forest, and multicolored rainbows can be enjoyed
by anyone who has eyes with which to see them. But by studying the branch of
physics called optics, which deals with the behaviour of light and other
electromagnetic waves, we can reach a deeper appreciation of the visible world. A
knowledge of the properties of light allows us to understand the blue color of the
sky and the design of optical devices such as telescopes, microscopes
Some part of the optics can be understood if we assume that light travels in a straight line and it bends
abruptly when it suffers reflection or refraction
Light is electromagnetic wave (proposed by Maxwell). It consists
of varying electric field and magnetic field.
When light rays strike the boundary of two media such as air and glass, a part of light is turned back
into the same medium. This is called Reflection of Light
The incident ray, the reflected ray and the normal at the point of incidence lie in the
same plane. This plane is called the plane of incidence (or plane of reflection). This
Let us call the side in which incident rays are present as incident side and the side in which reflected
( refracted) rays are present, as reflected (refracted) side
Plane mirror is formed by polishing one surface of a plane thin glass plate .It
is also said to be silvered on one side.
Characteristics of image due to reflection by a plane mirror
An extended object like AB shown in figure is a combination of infinite
number of point objects from A to B. Image of every point object will be
formed individually and thus infinite images will be formed
Relation between velocity of object and image
Images formed by two plane mirrors
Locating all the images formed by two plane mirrors
Spherical Mirror is formed by polishing one surface of a part of sphere.
Depending upon which part is shining the spherical mirror is classified
as (a) Concave mirror, if the side towards center of curvature is shining
and (b) Convex mirror if the side away from the center of curvature is
shining.
Following facts are useful in ray tracing. If the incident ray is parallel to the principle axis,
the reflected ray passes through the focus.
We are using co–ordinate sign convention
Formula for Reflection from spherical mirrors
When the light changes its medium, some changes occurs in its properties, the
phenomenon is known as refraction
The incident ray , the normal to any refracting surface at the point of incidence and the
refracted ray all lie in the same plane called the plane of incidence or plane of refraction.
When light moves from denser to rarer medium it bends away from normal
Deviation of a Ray Due to Refraction
Principle of Reversibility of Light Rays
When light passes through a parallel slab, having same medium on both sides, then
At near normal incidence (small angle of incidence i) apparent depth (d) is given by:
Refraction through a composite slab (or refraction through a
number of parallel media, as seen from a medium of R. I. n0)
Critical angle is the angle made in denser medium for which the angle of refraction in rarer medium is
90º. When angle in denser medium is more than critical angle, then the light ray reflects back in denser
medium following the laws of reflection and the interface behaves like a perfectly reflecting mirror
A homogeneous solid transparent and refracting medium bounded by two
plane surfaces inclined at an angle is called a prism
The angular splitting of a ray of white light into a number of components and spreading in different
directions is called Dispersion of Light. [It is for whole Electro Magnetic Wave in totality]. This
phenomenon is because waves of different wavelength move with same speed in vacuum but with
different speeds in a medium.
Numerical data reveals that if the average value of ? is small
Dispersion without deviation (Direct Vision Combination) Deviation without dispersion (Achromatic Combination
(Only for your knowledge and not of much use for JEE)
Ordered pattern produced by a beam emerging from a prism after refraction is called Spectrum. Types
of spectrum:
For paraxial rays incident on a spherical surface separating two media
The same sign of v and u implies that the object and the image are
always on the same side of the interface separating the two media. If we write the above
formula as
A thin lens is called convex if it is thicker at the middle and it is called concave if it is thicker at the
ends.
Transverse magnification (m) of (of dimension perpendicular to principal
axis) is given by
Fix an object of small height H and a screen at a distance D from object
(as shown in figure). Move a converging lens from the object towards the
screen. Let a sharp image forms on the screen when the distance
between
The equivalent focal length of thin lenses in contact is given by
The combination of lens and mirror behaves like a
mirror of focal length ‘f’ given by
THE SUN RISES BEFORE IT ACTUALLY RISES AND SETS AFTER IT ACTUALLY SETS
