U4AOS1 Topic 15: Refraction and Reflection

Refraction is the apparent bending of light. It's the reason why a pencil will look like its bent when you put it in a cup of water.


Reflection is when light bounces off a surface. When light reflects, the light will always leave at the same angle that it came to the surface.



The Reflective Index is the ratio of the speed of light in a vacuum and in a medium. As light does not travel at the same speed in all materials. It is given by


n=cvn=\frac{c}{v} 


It can also be calculated through mediums by using 


n1v1=n2v2n_1v_1=n_2v_2




Snell's Law is used to relate the angle of incidence to the angle of refraction and is calculated using

n1sin(θ1)=n2sin(θ2)n_1sin(\theta_1)=n_2sin(\theta_2)

The Critical Angle is the angle at which light will stop refracting and start to reflect. It is calculated through

θc=sin−1(n2n1)\theta_c=sin^{-1}(\frac{n_2}{n_1})


Note: The fraction inside the inverse sin cannot be greater than 1. If this is the case, you may have your values the wrong way around or it's not possible.



If n1>n2n1>n2n2  then light will 'bend' away from the normal. 

If n2>n1n_2>n_1 then light will 'bend' toward the normal.


Use the simulation below to assist you.

Created with GeoGebra®, by Lenore Horner, Link