When the ray of light travels from air to glass slab and strikes the surface of separation at 90 degree , then it ..........
reflects to air
When the ray of light travels from air to a glass slab and strikes the surface of separation at a 90-degree angle (perpendicular to the surface), then it undergoes a phenomenon called total internal reflection.
Total internal reflection occurs when the angle of incidence is larger than the critical angle. The critical angle is defined as the angle of incidence that causes the refracted ray to bend along the surface, rather than passing into the second medium.
To calculate the critical angle, you need to know the refractive index of the two mediums, in this case, air and glass. The refractive index is a property of the medium that describes how it changes the speed and direction of light passing through it.
The critical angle can be found using the following formula:
critical angle = arcsin(n2/n1)
Where n1 is the refractive index of the medium from which the light is coming (in this case, air), and n2 is the refractive index of the medium into which the light is entering (in this case, glass).
For example, the refractive index of air is approximately 1.00, and the refractive index of glass is typically around 1.50. Using these values, we can calculate the critical angle:
critical angle = arcsin(1.50/1.00) = arcsin(1.50) ≈ 41.8 degrees
So, if the angle of incidence is greater than 41.8 degrees when light travels from air to a glass slab, total internal reflection will occur at the surface of separation.