Colour
Within the visible light range of the Range of all possible frequencies of radiation, eg ultraviolet light is part of the EM spectrum., there is a A series of similar waves arranged in order of wavelength or frequency. of colour. This is a Variation that shows a wide range of intermediate values between two extremes. They can be measured. range of colours. In order of increasing The number of waves produced each second. The unit of frequency is hertz (Hz). and decreasing The length of a single wave, measured from one wave peak to the next, or one wave trough to the next. these are given as:
- red
- orange
- yellow
- green
- blue
- indigo
- violet
Each colour within the visible light spectrum has its own narrow band of wavelength and frequency.
Absorption of light
Waves can be Energy is 'taken-in' by the material and the internal energy of the material will increase, eg infrared radiation from the Sun is absorbed by the surface of the Earth. at the boundary between two different materials. When waves are absorbed by a surface, the energy of the wave is transferred to the particles in the surface. This will usually increase the The total kinetic energy and potential energy of the particles in an object. of the particles.
When white light shines on an Not transparent or see-through. object, some wavelengths or colours of light are absorbed. These wavelengths are not detected by our eyes. The other wavelengths are reflected, and these are detected by our eyes.
For example, grass appears green in white light:
- red, orange, yellow, blue, indigo and violet are absorbed by the grass
- green light is reflected by the grass and detected by our eyes
Transmission of light
Waves can also be A wave is passed across or through聽a material聽(medium), eg light waves are transmitted through air, glass and water. at the boundary between two different materials. When waves are transmitted, the wave continues through the material. Air, glass and water are common materials that are very good at transmitting light. They are Able to be seen through. because light is transmitted with very little absorption. Allows light to pass through but is not completely clear. materials transmit some light but are not completely clear. Lamp shades, shower curtains and window blinds are often translucent objects.
Colour filters
When white light passes through a coloured filter, all colours are absorbed except for the colour of the filter. For example, an orange filter transmits orange light but absorbs all the other colours. If white light is shone on an orange filter, only the orange wavelengths will be observed by the human eye.
Coloured objects in coloured light
An object appears to be black if it absorbs all the wavelengths of visible light. For example, an object that appears blue in white light will appear black in red light. This is because the red light contains no blue light for the object to reflect.