physics light question

[thefifteenth]

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Hi, why do longer wavelengths with lower frequency move faster through a medium and thus bend less dramatically at the medium interface? Also, why are longer wavelengths diffracted the most?
I found this in my EK notes and I don't really understand this. Any help is appreciated. Thanks in advance

 

[viper420]

ok first thing that you must know is that when a wave passes from one medium to another ONLY the speed changes, while the frequency stays the same, therefore if the speed increase the wavelength also has to increase (c= frequency X wavelength), therefore if the wave has a longer wavelength its speed will also be greater.

As far as the longer wavelength being diffracted more im not really sure.

 

[mosquitoman]

like you said V = lambda * freq

if it moves slower, lambda is lower

n = c/v so if it moves slower

n is greater

due to snell's
n1sino1 = n2sino2

or n1/sino2 = n2/sino1
if n2>n1
then sino2 must be less than sino1

the lower the lambda, the slower the V, the greater the n, the lower the corresponding sintheta

this means the lower theta will be

remember theta is the angle between the normal so the lower it is the more it has been deflected

 

[silverlion]

As far as equations go, this is an OK explanation because it can be used as a method to remember the trend. But I think this is cyclic logic and not the real answer per se. Refractive index n can be determined using the equation n = c/v, BUT The equation does not explain why the refractive index is higher in the case of these media.

I started reading stuff on wikipedia related to refractive indices and its all pretty complicated...so lets just stick to mosquitoman's formula...