REFLECTION, REFRACTION AT PLANE SURFACES

LAWS OF REFLECTION

 The angle of incidence is equal to angle of reflection.

 The incident ray, Normal and Reflected ray ray all lie in one plane. 

PROPERTIES OF IMAGE FORMED BY PLANE MIRROR

1.  The image formed by a plane mirror is "virtual", "erect" and laterally reversed.
2.  The size of image is equal to size of object.
3.  The image is as far behind the mirror as the source is in front of it.
4.  When the plane mirror is rotated through certain angle, the reflected ray turns through double the angle.
5.  When two plane mirrors are kept facing each other at an angle '𝛳 ' and an object is placed between them, multiple images of the object are formed as a result of multiple successive reflections.

            a) If (360/𝛳) is "even", then no. of images is given by n = (360/𝛳)-1

            b)  If (360/𝛳) is "odd", then following two situations arise 

     

                   i) If object lies symmetrically, then n = (360/𝛳)-1

                  ii)  If object lies unsymmetrically, then n = 360/𝛳

            c) When two plane mirrors are placed parallel to each other, then  

                 n = (360/0) = ∞ (infinite no. of images)

Note:- 

I) The point object for a mirror is a point from which the rays incident on mirror actually diverge or towards which the incident rays appear to converge.

II) An optical image is a point where rays of light either intersect or appear to do so.

REFRACTION OF LIGHT

The Refracted ray bends towards the Normal when the second medium is denser than first medium and vice versa.

The deviation 'D' suffered by refracted ray is given by D =  i-r

LAWS OF REFRACTION

1. The Incident ray, the Refracted ray and the Normal to surface separating two media lie in one plane.

2. Snells Law: For any media, the ratio of sine of angle of incidence to sine of angle of refraction is a constant for a light beam of particular wavelength.

sini/sinr = 𝜇2/𝜇1 = constant

Refractive index 𝜇 = velocity of light in vacuum / velocity of light in medium

Nature of orbits of satellites for different speeds

Let

'V' be velocity with which a body is projected from Earth.
Vs be minimum velocity of object to orbit around earth
Ve be escape velocity from surface of earth

then if,

i)  V < Vs ---  body falls to ground
ii) V = Vs --- body rotates round earth in circular orbit closer to surface of Earth
iii) Vs < V < Ve --- body revolves in elliptical orbit
iv)  V = Ve ----------body just  escapes from gravitational field
v)  V > Ve  --------- body moves in interstellar space with velocity equal to √V² -Ve²
vi)  V<Ve  ---------- Total energy of body is negative
vii)  V =Ve ---------- Total energy of body is zero