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Light - Reflection And Refraction


MeritNation Revision Notes for Class X CBSE Exams CCE India Copyright MertiNation

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									                  10. Light - Reflection and Refraction

Laws of Reflection

       (i)    i=r
       (ii)   AO, OP, and OB are co-planar

Spherical Mirror
    Centre of curvature = Centre of the sphere of which the spherical mirror is a

    Pole = Mirror centre

    Focus = Where parallel rays (parallel to the principal axis) meet or appear to
     meet after reflection
    Principal Axis= The imaginary line that runs through the pole and the center
     of curvature of a spherical mirror.
    Distance of focus from the pole is half the radius of curvature.
 Concave mirror and Image
   All images are real and inverted, except when the object is between the
    focus and the pole.
    Image size = object size when the object is at the centre of curvature

   Uses:
    o Torch reflector
    o Search light
    o Vehicle headlight
    o Dentist’s mirror
    o Shaving mirror
 Convex mirror and Image
    No real image
    No inverted image
    All images are diminished
    Uses:
     o Rear-view mirror
     o Security mirror
       Mirror formula
          1 1 1
            
          f v u
          For concave mirror, f = –ve and for convex mirror, f = +ve
                        Image height v
    Magnification                  
                        Object height u
       For real image, v = –ve
       Virtual image, v = +ve

 Refraction Laws
                                  (i) AO, OB, and MON
                                      are co-planar                Incident ray,
                                                                   refracted ray, and
                                         sin i                     normal to the
                                  (ii)         = constant          interface at
                                         sin r
                                         (Snell’s law)             incident point are

 Refractive index (RI)
                                  velocity of light in medium I v1
      1    ( of 2 w.r.t. 1) =                                 
                                  velocity of light in medium II v 2
      (Absolute RI when medium I = Vacuum = air)
      (Light speed {vacuum} = 3 × 108 m/s)

                                                  Medium (Optically denser) =  >

                                                         Optically rarer =  < 1

                                                   path of a ray when there is no change in
 Centre of curvature = Centre of the sphere of which the lens surfaces is a part of
  (Same as Spherical mirror)
 Focus = Where parallel rays meet after refraction (On principal axis = principal
 Convex lens and Image
    Virtual and erect images – when the object is placed between F1 and the
     optical centre (Magnifying glass)
    Image size = object size when object at 2F (=Centre of curvature)

 Concave lens and Image
   Virtual and erect at all object positions
 Lens Formula
  For   concave lens f = –ve
        convex lens f = +ve
 Magnification
      Im age height v
  m                (Same as mirror)
      Object height u
 Lens power
                        1      f = –ve for concave
  P Unit dioptre  
                        f  in m 


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