Ray Optics -1 Flashcards
laws of reflection
The
angle of reflection (i.e., the angle between reflected
ray and the normal to the reflecting surface or
the mirror) equals the angle of incidence (angle
between incident ray and the normal). Also that
the incident ray, reflected ray and the normal to
the reflecting surface at the point of incidence lie
in the same plane
for curved mirrors
i) normal
ii)paraaxial
iii)focus
iv) focal plane
The normal in this case
is to be taken as normal to the tangent to surface
at the point of incidence. That is, the normal is
along the radius, the line joining the centre of curvature of the mirror to
the point of incidence
We assume that the rays
are paraxial, i.e., they are incident at points close to the pole P of the mirror
and make small angles with the principal axis.
If the parallel paraxial beam of light were incident, making
some angle with the principal axis, the reflected rays would converge (or
appear to diverge) from a point in a plane through F
plane passing through focus and pependicular to the principal axis
practical applications of spherical mirrors
convex mirror:
- used in street light- to diverge light
- drivers mirror due to larger field of view / side view mirror
concave mirror:
- car head light/ search light/telescope/ colar cooker
- ent mirror
- shaving/make up mirror
- ophthalmoscope
refraction
change in path of light when it moves from one medium to another
whenever light falls on the interphase between two media, some of the light is refracted
laws of refraction
(i) The incident ray, the refracted ray and the
normal to the interface at the point of
incidence, all lie in the same plane.
(ii) The ratio of the sine of the angle of incidence
to the sine of angle of refraction is constant.
Sini/sinr=n21
sini/sinr=n2/n1
diff b/w optical and mass density
Optical density should not be
confused with mass density, which is mass
per unit volume. It is possible that mass
density of an optically denser medium may
be less than that of an optically rarer
medium (optical density is the ratio of the
speed of light in two media). For example,
turpentine and water. Mass density of
turpentine is less than that of water but
its optical density is higher.
refractive index
absolute refractive index of a medium is the ratio of speed of light in vacuum to the speed of light in the medium.
it is independent of angle of oncidence. it depends on nature of medium and the wavelength of light. frequency same
glass slab
acc principle of reversbility of light, when the final path of a ray after multiple refraction and reflection is reversed, it retraces its path.
the light ray emergesprallel to the incident ray, but it shifted by a distance called as lateral displacement/shift.
it depends on thickness of slab and on angle of incidence
real depth and apparent depth
an object in a denser medium appears higher thnan real depth due to refraction.
when the object is in a rarer medium, the object appears furhter away than its already height.
what is total internal reflection
it is the phenomenon of reflection of light into a denser medium from the interface of this denser medium and a rarer medium
When light gets reflected by a surface, normally some fraction of it gets transmitted. The
reflected ray, therefore, is always less
intense than the incident ray, howsoever
smooth the reflecting surface may be. In
total internal reflection, on the other hand,
no transmission of light takes place.
critical angle
critical angle for a pair of media in contact is the angle of incidence in the denser medium to which the angle of refraction in the rarer medium is 90.
when the light is incident at the interface from the denser medium, at an angle greater than the critical angle then it undergoes total internal reflection.
For values of i larger than ic , Snell’s law of refraction cannot be satisfied, and hence no refraction is possible
totally reflecting glass prism
Prisms designed to bend light by 90° or by 180° make use of
total internal reflection [Fig. 9.13(a) and (b)]. Such a prism is also
used to invert images without chxanging their size [Fig. 9.13(c)].
In the first two cases, the critical angle i
c for the material of the prism
must be less than 45°. We see from Table 9.1 that this is true for both
crown glass and dense flint glass.
These are isosceles right angle prisms.
working of optical fibres
Optical
fibres too make use of the phenomenon of total internal reflection.
Optical fibres are fabricated with high quality composite glass/quartz
fibres. Each fibre consists of a core and
cladding. The refractive index of the
material of the core is higher than that
of the cladding.
When a signal in the form of light is
directed at one end of the fibre at a suitable
angle, it undergoes repeated total internal
reflections along the length of the fibre and
finally comes out at the other end (Fig.
9.14).
Since light undergoes total internal
reflection at each stage, there is no
appreciable loss in the intensity of the light
signal.
Optical fibres are fabricated such
that light reflected at one side of inner
surface strikes the other at an angle larger
than the critical angle.
Even if the fibre is
bent, light can easily travel along its length.
Thus, an optical fibre can be used to act as
an optical pipe.
main requirement of optical fibres
The main requirement in fabricating optical fibres is that there should
be very little absorption of light as it travels for long distances inside
them. This has been achieved by purification and special preparation of
materials such as quartz. In silica glass fibres, it is possible to transmit
more than 95% of the light over a fibre length of 1 km.
uses of optical fibres
i) optical fibres are extensively used for
transmitting audio and video signals through long distances.
ii) Optical fibres are extensively
used for transmitting and receiving electrical signals which are converted to light
by suitable transducers.
iii)optical
fibres can also be used for transmission of
optical signals. For example, these are used
as a ‘light pipe’ to facilitate visual examination
of internal organs like esophagus, stomach
and intestines. used in laparoscopic surgeries
