Home » HANDBOOK OF O LEVEL PHYSICS » UNIT 14: REFLECTION AND REFRACTION OF LIGHT

UNIT 14: REFLECTION AND REFRACTION OF LIGHT

  • Beam: It is a bundle of rays.

  • Shadows: They are the dark areas that are formed when light is blocked.

  • We can see

    • luminous objects because they produce light

    • non-luminous objects when they reflect light

  • Regular and irregular reflections

    • Smooth, shiny and polished surfaces (e.g., mirror) give a regular reflection.

    • Rough, dull and unpolished surfaces (e.g., paper) give an irregular reflection.

  • Second Law of Reflection: The angle of incidence is equal to the angle of reflection.

i = r

  • Plane mirrors

    • Characteristics of image in a plane mirror

      • Same size as the object.

      • Same distance behind the mirror as the object in front of the mirror.

      • Upright

      • Virtual

      • Laterally inverted ( i.e., left appears right and vice versa.)

    • Applications of plane mirrors

      • Eye-sight testing in a small room

      • Removing parallax error in instrument scales

  • Real Image: It is an image that can be formed on a screen because rays converge on image.

    • Examples: Projector / Photocopier / Camera

  • Virtual Image: It is an image that cannot be formed on a screen because rays only appear to come from image.

    • Examples: Magnifying glass / Reflection in a mirror

  • Refraction: It is the bending of light when it enters or exits a medium.

  • When light slows down it bends towards the normal………….when light speeds up it bends away from the normal.

  • Second Law of Refraction: The ratio of the sine of the angle of incidence in one medium to the sine of the corresponding angle of refraction in the other medium is a constant value.

  • Refractive index (of a medium): It is the ratio of the sine of the angle of incidence in vacuum (or air) to the sine of angle of refraction in the medium.

    • You use the formula n = (sin i / sin r) when light goes from vacuum (or air) to an optically dense medium
    • You use the formula (1/n) = (sin i / sin r) when light goes from an optically dense medium to vacuum (or air)
    • Value of n is always greater than 1.
    • Greater the value of n, greater is the refraction (bending).
  • Consequences of refraction

    • Swimming pools appear shallower.

    • Objects appear bent.

    • Mirages

    • Rainbows

    Note: Rainbows are due to refraction, total internal reflection and dispersion of white light.

  • Critical angle: It is the angle of incidence in the optically denser medium for which the angle of refraction in the optically less dense medium is 90o.

  • Total internal reflection: All the ray reflects back into the denser medium when the angle of incidence in the optically denser medium is greater than the critical angle.

    • Application in fibre optic cables: Information is passed in the form of (visible) light that shows total internal reflection. Optical fibers are used in telecommunications because they have following advantages over copper wires:

        • more data per second

        • more secure

        • less attenuation (so boosters are further apart)

        • less interference (e.g., cross-talk)


If you are interested in any of our services, then find out ways of contacting us.


Have questions? See our compilation of questions and answers.