Spectrum

D. Crowley, 2008

Spectrum

To know how a spectrum (rainbow of colours) is made

Colours

What are the colours of the rainbow?

Can you make a rhyme to remember them?

RedOrangeYellowGreenBlueIndigoViolet

RichardOfYorkGaveBattleInVein

Dispersion

• White light can be split up to form a spectrum by using a prism (a triangular block of transparent material)

• Shine a ray of bright white light at a prism and move the prism until colours appear – draw a diagram showing what you have observed

Dispersion (Splitting Light)

• A prism splits a ray of white light into a spectrum of colours, known as dispersion

Waves

• What is the difference between each colour of the spectrum?

Each colour has a different wave length ()

Blue

Green

Red

Dispersion

• Why do the colours appear after they have travelled through a prism?!

• The different colours of light have different wavelengths, this means they are bent (refracted) by different amounts - which colour is refracted the most?

Red light is refracted least because it has the longest wavelength

Violet light is refracted the most because it has the shortest wavelength

Dispersion

• Light can be dispersed to give a spectrum of colours (using a prism)

• Your challenge is to recombine this dispersed light – how could you do this?

Newton’s Disc

• Spinning the disc quickly combines all the wavelengths of light – making white light via colour addition

Newton’s Disc @ Home

Colour in a paper or card circle with the colours of the spectrum

Using string or a pencil spin your disc around…

Rainbow

• In the laboratory we used a prism to split the wavelengths of light to produce the colours

• How do rainbows form in the natural world, when there are no prisms?!

• Rainbows form because of water molecules which act like miniature prisms (to see a rainbow the water droplets must be between you and the light)