Class - 10

Science - Physics

Chapter :- 9

Light - Reflection and Refraction

Notes



Reflection :- The bouncing back of light when strikes on a polished surface is called Reflection of Light.

Refraction :- The change in the direction of light ray when passing from one medium to another is called Refraction of Light.

Refraction causes due to the change in the speed of light.

 

Principal Axis :- The line joining the Pole (P) and Center of Curvature (C).

Pole (P) :- The  center of spherical mirror.

Centre of Curvature (C) :- The Center of a hollow glass sphere of which the mirror a part.

Focal Length (f) :- The distance between  the Pole (P) and the Focus (F).

Optical Center (O) :- The point on a lens through which a ray of light passes without diviation.

 

Relation between Focal length (f) and Radius of curvature (R):

f = R/2 or R = 2f


Formulas related to Mirror :-

      ·         Mirror Formula :-

         1/f = 1/v + 1/u

 

      ·         Magnification (m) :-

         m = h’/h = -v/u

 

Rules to Form image by Concave Mirror :-

  1.              A ray of light going parallel to Principal Axis, after reflection it will pass through Principal Focus (F).
  2.              A ray of light passing through the Principal Focus (F), after reflection it will become parallel to Principal Axis.
  3.              A ray of light passing from Center of Curvature (C), after reflection it will go back along the same path.

 

Rules to Form image by Convex Mirror :-

  1.           A ray of light going parallel to Principal Axis, after reflection it will appear to diverge from Principal Focus (F).
  2.            A ray of light appears to going towards the direction of Principal Focus (F), after reflection it will become parallel to the Principal Axis.
  3.             A ray of light appears to going in the direction of Center of Curvature (C), after reflection it will go back along the same path.

 

 

Formulas related to Lens :-

       ·         Lens Formula :-

          1/f = 1/v – 1/u

 

       ·         Magnification (m) :-

          m = h’/h = v/u

 

        ·         Power of Lens (P) :-

           P = 1/f

 

 

Rules to Form image by Convex Lens :-

  1.  A ray of light parallel to the Principal Axis, after refraction it will passes through Principal Focus (F2).
  2.  A ray of light passing through a Principal Focus (F1), after refraction will emerge parallel to the Principal Axis.
  3. A ray of light passing through the Optical Center (O), after refraction will pass without any bend or deviation.

 

Rules to Form image by Concave Lens :-

  1.                A ray of light parallel to the Principal Axis, after refraction the ray appears to diverge from Principal Focus (F1).
  2.              A ray of light appearing to meet Principal Focus (F2), after refraction will emerge parallel to the Principal Axis.
  3.            A ray of light passing through the Optical Centre (O), after refraction will emerge without any bend or deviation.