Transmission: Reflection (GCSE Physics)

Transmission: Reflection

Reflection

• Waves are reflected by the same angle. When a wave reaches a boundary, it will be reflected by the same angle at which it arrived. We can put this more simply by calling the arrival angle as the angle of incidence, and the reflected angle as the angle of reflection. They are linked by the following relationship.

• There are 2 types of reflection. When we talk about reflection, there can be two types. They are called specular reflection and diffuse reflection. Specular reflection occurs when waves hit a smooth surface, whilst diffuse reflection occurs when the waves hit a distorted, uneven surface.
• The 2 types of reflected waves are different. When there is specular reflection, the reflected wave will have the same angle of reflection as angle of incidence. When there is diffuse reflection, the reflected wave will have a different angle of reflection compared to the angle of incidence.

Total Internal Reflection

As we have seen before, as light moves from a more dense medium to a less dense medium, light is refracted.

Total internal reflection occurs when all the light is completely reflected. When the ray of light changes from just refraction to total internal reflection, we now name the angle of incidence the critical angle.

This means that in total internal reflection, the angle of incidence is greater than the critical angle.

The critical angle of a material can be found using the formula:

Where:

• refractive index, n
• critical angle, c

Optical Fibres

Optical fibres are made of two layers. The inner core is made of high purity glass and the outer layer is made of a material known as cladding.

The cladding has a lower refractive index and is less dense than the inner glass core. This means that light rays passing through the core are totally internally reflected, where they enter at an angle greater than the critical angle.

This allows the light to be continuously reflected throughout the whole optical fibre, therefore acting like a mirror.

Optical fibres can be used in endoscopes in surgical procedures. An endoscope is a camera which uses light to form a picture of the inside of someone’s body. They can also be used in carrying large amounts of information for high speed internet.