# A Glass Prism Of Refractive Index 1.5 Is Immersed In Water (Refractive Index 4/3). A Light Beam Normally On The Face Ab Is Totally Reflected To Reach On The Face Bc If

A light beam incident generally on the face AB is reflected to reach on the face BC if $\Theta \geq \Theta _{c}$

The beam is grazed on face BC, e = $90^{\circ}$

Refractive index of water, $n_{1} = \frac{4}{3}$

Refractive index of prism, $n_{2} = 1.5$

By using Snell’s law of refraction,

$n_{2}sin\Theta _{c} = n_{1}sin e$

= $sin\Theta _{c} = \frac{8}{9}$

For total internal reflection, $sin\Theta \geq sin\Theta_{c}$

Hence, $sin\Theta \geq \frac{8}{9}$

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