The Electromagnetic Spectrum Optics Lesson # 1 The Electromagnetic Spectrum

The Sun The sun produces huge amounts of energy, and some of this energy is in the form of light. The sun’s light travels through the vacuum of space and reaches earth, providing enough energy to heat the earth’s surface and allow photosynthesis to occur on land and in water.

Properties of Light Light travels at very high speeds – so fast that if something was travelling at the speed of light, it could circle around the Earth 7.5 times in one second! Light always travels in straight lines. Light does not need to travel through a medium (a physical substance used for energy transfer) – it can travel through the vacuum of space. Light energy is transferred through radiation. Light shows wave-like properties.

Parts of a Wave

The Electromagnetic Spectrum An electromagnetic wave is a wave that has both electric and magnetic parts, does not require a medium, and travels at the speed of light. Visible light, along with other types of waves such as radio waves, X-ray, and UV radiation are all part of an energy classification system called the electromagnetic spectrum. Waves on the left of the spectrum are longer and slower (lower frequency), such as radio waves, microwaves, and infrared waves. Waves on the right of the spectrum are shorter and quicker (higher frequency), such as ultraviolet waves, x-ray waves, and gamma ray waves.

Seeing Light Visible light is in the centre of the spectrum, and is the only light we can see with the naked eye. Infrared light can be seen with “night-vision” goggles. Ultraviolet light can be seen through “black lights.” Scientists have been able to explore life on earth as well as deep space with the discovery of different forms of light energy.

Video The Electromagnetic Spectrum

The EMS

Types of Waves

Visible Light Visible light is also called “white light.” Visible light is composed of a continuous sequence of colours, making up the visible spectrum. 7 distinct colours can be seen – red, orange, yellow, green, blue, indigo, and violet (ROY G. BIV). Red is the least energetic (closest to infrared waves), and violet is the most energetic (closest to ultraviolet waves) part of the visible spectrum.

Colour Theory If the three primary colours of light are added together, white light is produced. These colours are red, blue, and green (not yellow!). Remember, colours of light are just waves of different energy (frequency) – they are not the same as mixing two paint colours together. If two of the primary colours are added together, secondary colours are produced. Red + Blue = Magenta Blue + Green = Cyan Green + Red = Yellow

Production of Light Most people think light can only come from the Sun – because it radiates its own light. This is called a luminous light source. Light actually enters your eyes from all objects that you see – it is being reflected. Most objects are seen this way, as they are non-luminous light sources.