Snell’s Law

Law of Reflection

When a wave is propagating through a medium and find a surface that is a boundary to another medium, part of the wave is reflected so it keeps propagating through the same medium and the other part propagates through the second medium.

Let’s have a closer look at the first part of the wave: the reflected wave.

The law of reflection states that the incidence angle î and the reflected angle î ’ are equal:

î=î ’


snell's law

The Snell’s Law

This law studies the refraction phenomenon. The angle of refraction, r, depends on the angle of incidence î and the relation between the refractive indexes of the media. The Snell’s law enunciates this relation as:

snells_equation As n=c/v (where c is the velocity of the light and v the propagation velocity of the medium):snells_equation_velocityIn addition, we know that  v = λf ( λ is the wavelength and f  the frequency):snells_indexes_relationSnell's agles

Conclusions about the Snell’s law

If v2 > v1 , the direction of the refracted wave moves away from the normal of the separation surface (r>i).

If v2 < v1 , the direction of the refracted wave moves towards the normal of the separation surface (r<i).

The wavelength changes in the different media (because the frequency stays constant).


Critical Angle and Total Reflection

The critical angle,  ic , is the angle of incidence needed so the angle of refraction is 90º.


If the angle of incidence is greater than the critic angle, there won’t be refraction: this effect is known as total reflection.

critical angle

We hope you found this post helpful and remember to check it before our next post, which will be a bit more complex: Normal Incidence over Conductors 🙂

Remember to leave a comment below or contact us if you have any question or want to add something! See you soon!


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