Skip to main content

REFLECTION OF LIGHT


 LIGHT REFLECTION 

Light is a form of energy, which gives us the power of vision.

In this chapter we will study the phenomena of reflection and refraction using the property of light i.e. straight line propagation (Light wave travel from one point to another, along a straight line).

Ray of light : It is a line in the direction of movement of light.
Beam of light : It is bucnh of rays of light.
Parallel beam : All the rays are parallel.

Reflection of Light
When the light is allowed to fall on highly polished surface, such as mirror, most of the light gets reflected.

Laws of Reflection

1. The angle of incidence is always equal to angle of reflection.

2. The incident ray, reflected ray and the normal to the reflecting surface at the point of incidence lie in the same plane.

Image formed by Plane Mirror (Plane reflecting surface)

1. Virtual (imaginary) & Erect : The image that do not form on screen.
Real images can be recorded on the screen.
2. Laterally inverted (The left side of object appear on right side of image)
3. The size of image is equal to that of object.
4. The image formed is as far behind the mirror as the object is in front of it.

Reflection of light by spherical Mirrors
Mirrors, whose reflecting surface are curved inward or outward spherically are called spherical mirror.
For example – Spoon The curved surface of shinning spoon can be considered as curved mirror.

If it is curved inward Act as concave mirror
If it is curved outward Act as a convex mirror.

Few Basic terms related to Spherial Mirror

  1. Principal axis : Line joining the pole and centre of curvature of the spherical mirror.
  2. Pole : The geometrical central point of the reflecting spherical surface. (aperture), denoted by (P).
  3. Aperture : The width of reflecting spherical surface.
  4. Centre of curvature : The centre of the hollow glass sphere of which the spherical mirror is a part is called as centre of curvature.
  5. Radius of curvature : The distance between the pole and the centre of curvature. i.e.
    PC = R or The radius of the hollow sphere of which the mirror is a part.
  6. Focus point : The point on the principal axis, where all parallel rays meet after reflection is called as Principal Focus or Focus. It is denoted by letter ‘F’.
  7. Focal length : The distance between the pole and focus point i.e. PF = f
  8. Relationship between focal length and Radius of curvature. 

Image Formation by Spherical Mirror

Before we learn the formation of image or ray diagram, let us go through few tips

(a) Remember, a ray of light which is parallel to principle axis always pass through focus (meet at focus) or vice-versa.

(b) A ray of light which passes through centre of curvature (it is also known as normal at the point of incidence on spherical mirror) will retrace their path after reflection.

(c) A ray of light falling on pole get reflected at the same angle on the other side of principal axis.

Note : A ray of light passes through centre of curvature of reflecting spherical surface always act as normal at the point of incidence. If we know the normal we can draw angle of incidence and angle of reflection
 

Note 1 : The image will only form when two or more rays meets at a point. Image formation by a concave mirror for different position of the object.
The ray diagrams given in NCERT Books are also good to be followed.

Image Formation by Concave Mirror

 


Image formation by Convex Mirror




Uses of Concave Mirror
1 Used in torches, search light and headlight of vehicle.
2. Used to see large image of face as shaving mirror
3. Used by dentist to see large images of the teeth
4. Large concave mirror used to focus sunlight (heat) in solar furnaces.

Uses of Convex Mirror:-
Used as rear-view mirror in vehicles because it gives erect image. Italso helps the driver to view large area.

Sign Convention for Reflection by Spherical Mirror

  1. The object is always placed to the left side of mirror.
  2. All distance should be measured from pole (P); parallel to principal axis.
  3. Take ‘P’ as origin. Distances measured

Right of the origin (+x-Axis) are taken positive
Left of the origin (–x-Axis) are taken negative

Perpendicular to and above principal axis (+y-Axis) are taken positive
Perpendicular to and below principal axis (–y-Axis) are taken negative

Mirror Formula




Where,

f = distance between F and Pole ( Focal length)
v = distance of image from Pole
u =distance of object from Pole
R = distance between centre of curvature and pole.


Magnification:-

It is expressed as the ratio of the height of the image to height of the object.

It is denoted by m 



Where, 

h' = image height from principle axis

h = Object height from principle axis


Few tips to remember sign convention for Spherical mirror

fuv
CONCAVE-ve(real)-ve(real)-ve(real)
+ve(virtual)
CONVEX+ve+ve+ve

h – is always +ve
h´ – is +ve for virtual , –ve for Real.

Comments

Post a Comment

Popular posts from this blog

  Force:-   It is defined as the acceleration to move the object from one position to another.                                                Or  The push or pull on an object with mass that causes it to change its velocity. Force is an external agent capable of changing the state of rest or motion of a body.                              Force = Mass × Acceleration                                  F = m × a Where, the terms are denoted by the follow...
Post a Comment
Read more

Tissue

The Formation of Tissues Cells form groups cells that need to perform a single task often group together. This grouping of cells together to perform a function efficiently is called a  Tissue . For Example , Muscles and Blood. The tissue cells have the same structure and they perform the same function. Tissues of Plants and Animals Plant Tissues Animal Tissues Plants do not move so their tissues are predominantly the ones that provide support to them so that they can stand erect. Animals need more energy as compared to plants because they are not stationary. Their tissues are the ones that can support movement. These tissues are made up of dead cells because dead cells can also provide mechanical strength to the plants and do not require much maintenance. The tissues in case of animals are made up of living cells so that they can move and perform several functions. Only certain parts of the plant can grow. The tissues present in such regions of and divide themselves and form new ti...
Post a Comment
Read more

Human Eye and the Colorful world

  HUMAN EYE : It acts like a camera, enable us to capture the colourful picture of the surroundings. An inverted, real image on light sensitive  is formed on the  Retina The Various Parts of Eye and their Functions 1. Cornea  : It is a thin membrane through which light enters. It forms the transparent bulge on the front of eyeball. Most of the refraction occurs at the outer surface of the cornea. 2.  Eyeball  :it is a convex lens, approximately spherical in shape, with a diameter of about 2.3 cm. It can alter its curvature with help of ciliary muscles. 3.  Iris : It is a dark muscular diaphragm that controls the size of pupil.It is behind the cornea.it helps in accommodation of light by changing the size of the pupil. 4.  Pupil  :It regulates and control the amount of light entering the eye. It is the black opening between aqueous humour& lens.BLack in colour. Light entering cannot exit. 5.  Crystalline eye lens  :Prov...
Post a Comment
Read more