Mammoth Memory

Snell's law in use

Snell's law in use can be simplified because in most text books medium going in is the medium of air.

Angle in and angle out of a light ray travelling between air and water.

NOTE: how `theta` relates to the angle going in against the normal line is different to the angle coming out against the normal line.


We have learnt that Snell's law is

`(sin\ \i\n\ \theta)/(sin\ \out\ \theta)=(n\ \(out))/(n\ \(i\n))`

But the refractive index `n` of air for all practicle purposes is one (1).

(Infact a vacuum is 1 and air is 1.0002926)

So most text books show Snell's law as being

`(sin\ \i\n\ \theta)/(sin\ \out\ \theta)=n\ \(out)`

Ray of incidence and ray of refraction travelling from air to water.

Angle of the incident = Angle of incidence `(i)`

Angle refracted = Angle of refraction `(r)`


Snell's law becomes:

`(sin\theta\i)/(sin\theta\r)=(n\ \m\e\d\i\u\m\ \w\a\t\e\r)/(n\ \m\e\d\i\u\m\ \a\i\r)`

Which becomes


Which becomes

`(sin\theta\i)/(sin\theta\r)=n` (refractive index of medium)



Most text books show Snell's law as

`n=(sin\ \i)/(sin\ \r)`

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