Waves - 6.2.6 Visible Light (Physics Only) (GCSE Physics AQA)

Visible Light (Physics Only)

Colours of Visible Light

• Visible light is split into colours. The visible light section of the EM spectrum is further divided into its own spectrum. In fact visible light is made up of a spectrum of 7 different colours.
• Each colour has a wavelength and frequency. Each of the 7 colours of visible light will have their own wavelength and frequency. Violet light has the shortest wavelength and the highest frequency, whilst red light has the longest wavelength and the lowest frequency out of visible light.

Reflection

The Two Types of Reflection

• 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.

Colour Filters

• Colour filters use wave properties. Colour filters use wave properties to change the colours of objects. They will absorb certain wavelengths of light, letting other wavelengths through.
• Wavelengths are absorbed or transmitted. Essentially, colour filters will absorb some wavelength and transmit the rest. When they do this, the colour filters are also effectively absorbing and transmitting colours at the same time.

Effects of Filters

• Objects can be viewed through filters. We can view various objects through colour filters. The colour filters will absorb some of the wavelengths of light and transmit the others.
• Appearance of objects can change. When objects are viewed through filters, they can change in appearance. More specifically, the colour of the objects will change depending on the colour of the filter that is used. When light passes through a red filter for example, the ‘red’ wavelength is transmitted, whilst the rest of the wavelengths are absorbed. This will make any object that is viewed through this filter appear red.

Appearance of Objects

White and Black Objects

• White objects have reflected wavelengths. If an object appears totally white, then all the wavelengths of light have been equally reflected by the object. This is because all the wavelengths of light will combine to form the colour white, resulting in the object appearing white.

• Black objects have absorbed wavelengths. If an object appears totally black, then all the wavelengths of light have been equally absorbed by the object. Since none of the wavelengths have been reflected, the object will appear black.

Transmission of Light

• Objects can be transparent. If the wavelengths of light are not reflected or absorbed by an object, then the object will appear transparent. The reason for this is that the object has actually transmitted the light, meaning that it is totally ‘see through’.

Colours of Objects

• Opaque object colours depend on reflection. Opaque objects often have different colours, which are dependent on the reflection of different wavelengths of light. For example, we can look at the colour of the grass. To us, grass appears green. This is because the grass is absorbing all wavelengths of light except for the colour green. This means that the colour green is reflected, making the grass appear green.
• Wavelengths can undergo different effects. When a wavelength reaches an object, it can undergo different effects. We have explored these effects in this section, but here is a brief summary:
  • Absorption / transmission: This is used in colour filters and can change the appearance of an object.
  • Transmission: If wavelengths of light are transmitted, this results in the object appearing transparent.
  • Reflection: If wavelengths of light are reflected, this results in the object appearing a certain colour.