# Part reflection part refraction

Again you don't need this in an exam it is just interesting to know.

When a ray of light travels from a fast medium, like air to water at different angles of incidence (degree to the normal) you will always get some surface boundary reflection and you will always get some refraction. It is just in different proportions depending on the angle. See below:

(Please note: In nearly all questions in exams at basic level the reflected is not taken into account)

At no angle bright beam.

(but some is reflected backwards 3%)

 Light ray in = 30^circ To the normal Reflected ray = -30^circ To the normal Dim reflection (5%) Refracted ray = 23^circ To the normal = Bright refraction

 Light ray in = 60^circ To the normal Reflected ray = -60^circ To the normal Dim reflection (10%) Refracted ray = 42^circ To the normal = Bright refraction

 Light ray in = 85^circ To the normal Reflected ray = -85^circ To the normal Bright reflection (70%) Refracted ray = 50^circ To the normal = Dim refraction

If you were to draw the amount of light refracted at the boundary when light travels from air to water you would get the following graph:

Light travelling from air to water.

Light travelling at a water surface at angles of incidence less than 50 degrees mostly penetrate the water. Above 50 degrees the percentage of light that is reflected increases steeply.

So if you stand at a lake edge and look down near your feet (i.e. steep angle of incidence) you will see details in the water and on the bottom of the pool.

As you look out across the lake (i.e. at a shallow angle of incidence) you can clearly see the reflection of the trees in the lake and little detail in the waters bottom.