Question

the Angle incidence at which a light at ray doesn't undergo
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Answer 1

When light falls perpendicularly or normally on the surface of a glass slab, it goes straight. There is no bending of ray of light on entering the glass slab or coming out of it. In this case angle of incidence and angle of refraction is zero.

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Answer 2

Answer:

when light falls perpendicularly or normaly on yhe surface of the glass slab it it goes straight there is no bending of ray of light on enterning the glass slab coming out of it in this case angle of incidence and angle of reflaction is zero