ColourColour November 12 th, 2009

Quick Starter - Lack of Colour Imagine you could only see in black and white. What are the possible implications this could have on your life? Would it rule out any careers for you? What dangers could there be?

Colour : splitting white light up

Explanation What happens? The white light ray is split into a spectrum of colours. This is known as DISPERSION. Why? The different colours of light have different wavelengths. Different wavelengths are refracted different amounts. Red light is refracted least. Violet light is refracted the most. Which colour is refracted the most? How do you remember the order of the colours? Richard Of York Gave Battle In Vain

Until now we have used the title ‘splitting white light up’. However this process has a scientific name. The splitting of white light into a spectrum of colours is called DISPERSION. But why does white light get dispersed? Colour : splitting white light up

Dispersion Each of the colours [ROYGBIV] has a slightly different waveform - what is different? They each have a different wavelength [ ].

Because the different colours of light have different wavelengths they are bent (refracted) by different amounts. But which colour do you think is bent the most? Red light is refracted least because it has a long wavelength. Violet light is refracted the most because it has the shortest wavelength. Dispersion

Colour : joining the colours back together Remember how you dispersed white light to give a spectrum of colours? Now do the opposite to it - you’ll need 2 prisms! A similar effect can also be seen using a colour wheel [or Newton’s disc].

Newton’s disc

Seeing colours We see objects by light striking an object and then reflecting into our eye. How do we see colour? Why does a red dress look red? Why does a green apple look green? How do we see objects like a book?

Primary Colours You can make any colour by mixing three colours. Do you know what they are? Red Green Blue The colours labelled in white text are the PRIMARY COLOURS. The colours labelled in blue text are called SECONDARY COLOURS. They can be made by mixing the primary colours Cyan Yellow Magenta

Red objects Why does a red snooker ball look red in white light? Remember white light is made of a spectrum of colours. The snooker ball absorbs all the colours of the spectrum EXCEPT red, so red light is reflected into our eye. The snooker ball appears red.

Green objects Why does a green snooker ball look green in white light? The snooker ball absorbs all the colours of the spectrum EXCEPT green, green light is reflected into our eye. The snooker ball appears green.

Look at the clothes below. What colour light is reflected by these clothes?

What colours are absorbed by this frog’s skin? What colours are reflected into your eyes? This part of the skin absorbs all the colours of the spectrum but reflects red light. This part of the skin absorbs all the colours of the spectrum and none are reflected.

What colours are absorbed by this flower? What colours are reflected into your eyes? This part of the flower absorbs all the colours of the spectrum but reflects yellow (a mixture of red and green) light. This part of the flower absorbs no colours, it reflects them all.

Filters Filters let certain colours of light pass through, but absorb all other colours. Object filter

Red, blue and green filters Red filters absorb all colours…. Blue filters absorb all colours…. Green filters absorb all colours…. … apart from red light… apart from blue light … apart from green light

Multiple Choice Questions

Which of the following is not a light source? A.The Sun B.A star C.Traffic lights D.A book

Which of the following is not seen by reflected light? A.Your hand B.Jupiter C.Light bulb D.The Moon

Which of the following is the most dense? A.Air B.Water C.Glass D.Lead

When light changes direction as it moves from one medium to another we call this effect what? A.Reflection B.Refraction C.Diffraction D.Total internal reflection

Which colour has the longest wavelength? A.Blue B.Indigo C.Yellow D.Red

Which colour below is refracted (bent) the least by a glass prism? A.Red B.Orange C.Yellow D.Green

Which of the following is not a primary colour? A.Red B.Blue C.Cyan D.Green

Which two primary colours make magenta? A.Red and cyan B.Red and yellow C.Red and blue D.Blue and violet