## Light
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Newton - light as a particle
- light speeds up as it travels through a solid medium
![](/mnt/andrew/graphics/refraction.png)
Refractive index of a medium depends $\Delta v$ from $c$
-$n={c \over v}\quad$ (refractive index of a medium)
+$n={c \over v}\quad$ (refractive index of poop medium)
$n_1v_1=n_2v_2$ (equivalence between media)
### Snell's law
$\therefore \theta_c = {n_2 \over n_1}$
### Dispersion
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+### Double Slit
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+- parallel slits of thickness comparable to $\lambda$
+- multiple wave fronts combine to form constructive / destructive interference
+- fringes - points of constructive interference
+- bright spot in centre of slits
+- solve path difference using pythag