Visible light, colour and scattering

In a nutshell

Visible light is the frequency range of the electromagnetic (EM) spectrum that humans can see. Humans see colour because objects reflect or absorb different frequencies of light.

Definitions

Key word	Definition
Opaque	Not able to see through it - no light can pass through.
Transparent	Able to see completely through it - light can pass through.
Translucent	Able to partially see through it - some light can pass through.

Colour

Visible light is the frequency range of the EM spectrum that humans can see. Within visible light, different colours have different frequencies and wavelengths.

Visible light spectrum

R	Red	Lowest Frequency	Highest Wavelength
O	Orange	$\bold\downarrow$	$\uparrow$
Y	Yellow
G	Green
B	Blue
I	Indigo
V	Violet	Highest Frequency	Lowest Wavelength

Tip: Use the mnemonic ROYGBIV ("Roy-Gee-Biv") to help remember the order of the colours!

The primary colours are Red, Green and Blue. If an object is a different colour, it will either be made up of a combination of the primary colours' wavelengths, or the specific wavelength of the colour.