RBSE Class 12 Physics Notes Chapter 9 Ray Optics and Optical Instruments

These comprehensive RBSE Class 12 Physics Notes Chapter 9 Ray Optics and Optical Instruments will give a brief overview of all the concepts.

RBSE Class 12 Physics Chapter 9 Notes Ray Optics and Optical Instruments

Reflection of Light:
Light is a form of energy which produces in us the sensation of sight and optics is the study of visible light.

Ray Optics:
Ray Optics is that branch of physics which is based on the rectilinear propagation of light.

Laws of reflection:
According tc the laws of reflection :
(i) Angle of incidence is equal to angle of reflection
i.e. i = r

(ii) Incident ray, reflected ray and the normal at the point of incidence all lie in the same plane.
If two plane mirrors are placed at an angle 6 and a point object is held between these two mirrors, then
No. of image formed
n = \(\frac{360^{\circ}}{\theta}\) - 1, if \(\frac{360^{\circ}}{\theta}\) is even integer
and n = \(\frac{360^{\circ}}{\theta}\) , if \(\frac{360^{\circ}}{\theta}\) is an odd integer. 

Spherical mirror:
Spherical mirror is a part of a hollow sphere, whose one side is reflecting and the other is opaque. They are of two types namely concave mirrors and convex mirrors.

Mirror formula:
For concave mirror and also for convex mirror, the mirror formula is
\(\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\)
where u is object distance, v is image distance and f is the focal length of the mirror.

Assumptions:
Following assumptions are made for driving mirror formula.

• Aperture of the mirror is small.
• Incident ray makes small angle with principal axis.
• Object lies on the principal axis.
• Object lies on left hand side of the mirror.

Magnification or linear magnification of a spherical mirror is the ratio of the size of the image formed by the mirror to the size of the object.
i.e m = \(\frac{\text { size of image }}{\text { size of object }}=\frac{\mathrm{I}}{\mathrm{O}}\)
Also, m = -\(\frac{v}{u}=\frac{f-v}{f}=\frac{f}{f-u}\)
So, m = \(\frac{\mathrm{I}}{\mathrm{O}}=\frac{v}{-u}=\frac{f-v}{f}=\frac{f}{f-u}\)