During refraction of light through the glass slab incident ray and emergent ray are parallel explain
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This is true if light passes through the interface between one medium into another medium, and back into the first medium through another interface parallel to the first one. An example I will use to illustrate why this happens is light passing from air into a rectangular glass slab, and back into air.
According to Snell’s law, we have:
sinisinr=μgμa …(i)
By the same law, we also have:
sinr′sine=μaμg …(ii)
We assume that PQ is parallel to SR (interfaces are parallel). Since N2N1 is perpendicular to PQ and N2'N1' is perpendicular to SR, N2N1 is parallel to N2'N1'. r=r′ follows from the equality of alternate interior angles.
From equations (i) and (ii), we have:
sinr′sine=sinrsini
Taking reciprocals of both sides:
sinesinr′=sinisinr …(iii)
Since r=r′, sinr=sinr′. Multiplying both sides of (iii) by sinr, we get:
sine=sini
Since both e and i are acute, their sines being equal implies that the angles are equal, e=i. This is the result we set out to prove.
Note that if we don’t assume that PQ is parallel to SR, our proof would not be valid, since sinesinr′=sinisinr …(iii) would not imply sine=sini. The proof would also be invalid if AE and FD are not rays in the same medium, because we would not be able to get sinr′sine=sinrsini from equations (i) and (ii).
9.5k Views · ·
Why are incident ray and emergent rays parallel in a glass slab?
Why is it that in a prism the emergent ray bends towards the base and not parallel to the incident ray?
Why is the emergent ray parallel to the incident ray for refraction through a rectangular glass slab?
What is an emergent ray?
Is the emergent ray from glass slab parallel to the incident ray?
There are a number of good answers here already. I would just like to provide a different way of looking at this.
Light rays are reversible. They travel exactly the same path if they are going in the opposite direction. So if light is refracted some angle going from, say, air to glass, it would refract exactly the same angle in the opposite direction going from glass to air.
Credit:
The bottom side of the slab is the reversed situation of going from glass to air.
If the two sides if the glass slab are parallel, then no new angles are introduced. The two refractions cancel out the changes in direction of the ray. But as you can see, the emergent ray is displaced laterally, although it’s parallel to the incident ray.
If you want a more mathematical proof, take a look at the other answers. Thanks for asking.
17.1k Views · · Answer requested by
Since the refracting surfaces are parallel to each othe the emergent rays are parallel.
The angle of incidence on the first surface { from air to glass} be i and the angle of refraction at the first surface be r.
Since the surfaces are parallel the ray inside the glass falls at the other surface at angle r and therefore the ray emerges at angle i that is the angle of incidence.
Therefore the incident ray is parallel to the emergent ray.
1.5k Views · · Answer requested by
The question pertains to refraction of a ray of light through a glass slab.
Let an ray of light be incident on the surface of a rectangular glass slab at an angle i, from air to glass interface. Part of the incident ray is reflected back into the air, and a part is refracted into glass medium and travelling through the glass emerges from the side opposite to the original side parallel to the side on which light was incident, and emerges at an angle of emergence e.
Since glass is optically denser than air, the refracted ray on entering the glass bends towards the normal and angle of refraction r is such that,
n = (sin i/sin r), where n is refractive index of glass wrt air.
The refracted ray travels undeviated through glass and is incident on the face parallel to first face at an angle of incidence = r and then gets again refracted at the second face and emerges at an angle e. Since the ray of light is going from a denser to a rarer medium, the angle e is greater than r, the angle of incidence.
Now, (sin r/ sin e) = refractive index of air wet glass =1/n .
Therefore,
n = (sin i/sin r )=(sin e/sin r )
Therefore,
Angle of emergence e = and of incidence i.
Oe =Incident ray
Óm=emergent ray
ABCD is the rectangular glass slab,
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