Physics - Reflection and Refraction
OCR A-Level Physics 2022
Labelling a reflection diagram
What is the Law of Reflection?
On a smooth plane, the angle of incidence is equal to the angle of reflection.
Labelling a refraction diagram
Why refraction happens
Why does refraction occur?
Because the wave changes speed when it passes from medium to another.
What is partial reflection?
A slight reflection off a surface that a wave is refracted through.
If a wave speeds up when it passes into a new medium, what happens to the angle of refraction?
It increases.
If a wave slows down when it passes into a new medium, what happens to the angle of refraction?
It decreases.
Wavelength changes during refraction and reflection
What happens to the wavelength of a wave if it speeds up when being refracted?
It increases.
What happens to the wavelength of a wave if it slows down when being refracted?
It decreases.
What happens to the wavelength of a wave if it bends away from the normal when being refracted?
It increases.
What happens to the wavelength of a wave if the angle of refraction decreases when passing into a new medium?
It decreases.
What happens to the wavelength of a wave when it is reflected?
It stays the same.
How can the frequency of a refracted wave stay the same if the wavelength changes?
The wave speed changes to compensate.
The refractive index and Snell’s law
What is the formula for the refractive index $n$ given the speed of light in a vacuum $c$ and the speed of light in the material $v$?
Informally, what does the refractive index of a material tell you?
How much you divide the speed of light by to get the speed inside the material.
Critical angle
What is the formula for the refractive index $n$ of a material in terms of its critical angle $c$?
Dispersion: refractive index depends on wavelength
Why is Snell’s law
\[n _ 1 \sin\theta _ 1 = n _ 2 \sin\theta _ 2\]
a lie?
Because $n$ is actually a function of wavelength $n(\lambda)$.
Why is the refractive index of a material actually a function of the wavelength, $n(\lambda)$?
Because different wavelengths of light travel at different speeds.