3B Scientific Light Box - Manual (Page 12)

12
The refractive index of the slab is calculated by
i i
r
sin
1
sin
sin =
= µ
The
∠i at this point is called the CRITICAL ANGLE of the medium and is the minimum angle of
incidence for which all light is reflected back into the optically denser substance, instead of emerging
into air.
• What do you expect ∠r
1
to be? What is it actually?
• The critical angle for water to air is 49°. By what angle should a fish rotate its head to see the
riverbank, if it initially sees the opposite river-bank?
Total internal reflection is used in the OPTICAL-FIBER technology, a well-developed method of
transporting light and other electromagnetic waves.
Total Internal Reflection – Prism:
The phenomenon of total internal reflection can be observed by
using any of the prisms.
The 45
°45°90° prism is a prism that can invert images and even reverse the direction of light.
r = 90 °
r
1
i
Fig. 11
1
2
3
3
2
1
Fig. 12