dear students now we’ll start with topic
of geometrical optics or ray optics. as an introduction about geometrical optics we can
write. it is the branch of physics. which describes. the light propagation. in terms
of. light rays. we’ll discuss soon about light rays which you have earlier studied
in your previous classes also. so geometrical optics is the branch of physics that describe
light propagation in terms of light rays. which are used. to theoretically. demonstrate.
rectilinear propagation of light. here we can say light rays are not practically, define
term, these are theoretical terms which are used to demonstrate rectilinear propagation
of light whenever we need to explain some phenomena on paper. so if we just talk about.
rectilinear propagation of light. this also you light have studied in your early classes.
this rectilinear propagation of light says that. the tendency. of light. is only to travel.
in straight line path. in homogeneous medium. whenever light enters in homogenous medium,
in rectilinear propagation of light in r-p-l. we can state. this is the tendency of light
only to travel in straight line path whereas in general light can also be treated like
a wave and in it can exhibit various phenomena like. scattering diffraction interference
but those are all wave nature of light. but here we talk about light as. rectilinear propagation
phenomena light in only rectilinear propagation phenomena, and. the whole. all the concepts
related to rectilinear propagation of light and reflection-refraction. which we’ll study
are. cumulatively known as geometrical optics, or ray optics. here the phenomena of rectilinear
propagation you can understand with the help of this situation. if we are given with. a
source of light say we consider here a candle and 3 cardboards here. and a screen behind
the cardboards. then in this situation we can say if in cardboard 1 there are various
holes. then the light which is originated from, flame of candle. will pass through these
holes and will create spots on the second cardboard whereas only 1 hole in the second
cardboard is coinciding with the path of light ray. which is passing through the central
hole of. first cardboard. correspondingly third card board also. so here we can see
there only be 1 spot produce on the screen because the light was travelling in straight
line. through various holes from the first board and it is obstructed by the second board.
bur only 1 path is available to reach the screen that’s why this is the straight line
path in which the light ray is reaching the screen and producing a spot. and this, light
ray or the path of this light we define as light ray in this situation. and in coming
section we’ll study in detail about. the ray and beams of light.