# a ray of light passes through a plane glass slab of thickness t and refractive index mu. the angle between incident and emergent ray is ?

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## 1 Answers

Saurabh Kumar
askIITians Faculty 2400 Points
9 years ago

Let us consider a light ray passing through a glass slab of certain thickness t. There is a change of the medium in this case twice. When the light Ray is entering from a into the glass slab it moves towards the normal. Again when it is moving away from the glass slab into the air it moves towards the normal.
This is happening as per the laws of refraction. According to the law when the light Ray is moving from rarer medium to denser medium it has to move towards the normal and vice versa.
After two reflections, it is quite possible that the emergent light Ray is parallel to the incident light Ray. The perpendicular distance between the two light rays within the glass slab is called lateral shift. We can determine the value of the lateral shift in terms of the thickness of the glass slab, angle of incidence and angle of refraction as shown below. Here we have used basic trigonometric definitions to get the required proof.

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