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Refraction at Plane Surfaces

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  • When a light ray is incident on a surface separating two transparent media, the ray bends at the time of changing the medium. The angle of incidence 'i' and the angle of refraction 'r' follow Snell's law.
  • When light ray travels from rarer to denser medium, it bends towards the normal & when light ray travels from denser to rarer medium, it bends away from the normal.
  • A point on the base of the beaker slightly appears to be raised from the real point, this is called apparent shift which is due to the refraction of light.
  • For certain angle of incidence in the denser medium, the angle of refraction will be 90 degree in the rarer medium. This specific angle of incidence in the denser medium is the critical angle.
  • For angle of incidence greater than the critical angle (in the denser medium), the light will be totally internally reflected in the same medium. This is called the 'total internal reflection of light'.


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