Tuesday, August 2, 2011

From water to air

1. redo the formulas below for water to air.
2. What is critical angle ?
3. Show how you get the critical angle formula.
4. Post your answers to this blog !


  1. 1. na/nw=va/vw
    2. The critical angle is the angle of incidence above which total internal reflection occurs. The angle between the normal and the ray is 90 degrees.
    3. The formula is derived because the angle between the normal on the less dense medium on top of the ray(refracted angle) is 90 degrees and the incident angle will form the formula of n = sin i/ sin r which is equals to 1 so if the values are rearranged, critical angle = 1/n.

  2. sin i/ sin r = na/nw

    since na = 1 and sin90 = 1, we have

    sin i = 1/nw

    which is the formula for critical angle

  3. If you work out the answer, i = 48.6 degrees

    Just memorise it. Use this value to check for water-air interface.