Question

(a) Show using a proper diagram how unpolarised light can be linearly polarised by reflection from a transparent glass surface.
(b) The figure shows a ray of light falling normally on the face AB of an equilateral glass prism having refractive index 3/2 , placed in water of refractive index 4/3 . Will this ray suffer total internal reflection on striking the face AC ?

Answer 1

i c  > 60° So total internal reflection does not take place .

Explanation:

(A)  When Unpolarized light is incident on glass surface the electric vectors will pass through. Thus incident light gets polarised.

(B) Total internal reflection on AC, if i c  < 60°

μ isin ic  = μ 2 sin 90°

3/2 sin ic = 4/3 (1)

sin ic = 8/9

ic = sin^-1 (8/9)

so i c  > 60°

So total internal reflection does not take place .

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What is total internal reflection?

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Answer 2

(a) Unpolarised light linearly polarised by reflection:

The image for unpolarised light is given in the image 1.

Refracted ray:

When unpolarised light fall on the polaroid, the electric vectors that are perpendicular to the surface gets polarised linearly whereas the electric vectors which are along the direction of the polaroid is absorbed by the surface.

Reflected ray:

When unpolarised light fall on the polaroid, the reflected ray is completely or partially polarised.

When unpolarised light fall on the polaroid, the reflected ray is completely polarised when it falls perpendicular to the refracted ray.

(b) Total internal reflection:

The figure given in the question is given in the image 2.

Conditions for total internal reflection:

• Light should pass from higher refractive index to lower refractive index.
• The angle of incidence is greater than critical angle (60°).

Now, the problem given is:

$a_{\mu w}=\frac{\mu_{w}}{\mu_{s}}$

$a_{\mu w}=\frac{4 / 3}{3 / 2}$

$\therefore a_{\mu w}=\frac{8}{9}$

$\mathrm{i}=\sin ^{-1}(\mu)$

$\mathrm{i}=\sin ^{-1}\left(\frac{8}{9}\right)$

$\therefore \mathrm{i}=62.73^{0}$

Since, the critical angle is greater than incidence angle, so, the total internal reflection does not takes place.