WAEC - Physics (1989 - No. 23)
The refractive index of a given transparent medium is 1.4. Which of the following is the minimum internal angle for total internal reflection to take place in the medium?
30o
36o
44o
46o
54o
Explication
Critical angle Sin \(\theta\)\(_c\) = \(\frac{n_2}{n_1}\)
where n\(_1\) = refractive index of the medium ( 1.4 given )
n\(_2\) = refractive index of the second medium( air ≈ 1.0)
Sin\(\theta\)\(_c\) = \(\frac{1}{1.4}\) ≈ 0.7143
\(\theta\)\ = Sin\(^{-1}\)( 0.7143) ≈ 45.58º ≈ 46º
The minimum internal angle for total internal reflection to take place in the medium is approximately = 46º