WALT about colour Boardworks Ltd 2003 Activity Lack

WALT: about colour © Boardworks Ltd 2003

Activity 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? © Boardworks Ltd 2003

Colour : splitting white light up 1. Shine a ray of bright white light at a prism, as shown above, and move the prism until colours appear. © Boardworks Ltd 2003

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. Which colour is refracted the most? How do you the order of the. In colours? Red light is Richard Ofremember York Gave Battle Vain refracted least. Violet light is refracted the most. © Boardworks Ltd 2003

Dispersion • Each of the colours [ROYGBIV] has a slightly different waveform - what is different? They each have a different wavelength [ ]. © Boardworks Ltd 2003

$Dispersion Because the different colours of light have different wavelengths they are bent (refracted)$

Dispersion 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. © Boardworks Ltd 2003

Subtractive Colour – Paints and Dyes © Boardworks Ltd 2003

Additive Colours - Light © Boardworks Ltd 2003

Newton’s disc © Boardworks Ltd 2003

Practical – Explore Colour • Shine light from the ray box through a colour filter on to different coloured objects and record the colour they appear. • Record results in a table. © Boardworks Ltd 2003

Seeing colours How do we see objects like a book? 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? © Boardworks Ltd 2003

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. © Boardworks Ltd 2003

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. © Boardworks Ltd 2003

Black objects Why does a black snooker ball look black in white light? The snooker ball absorbs all the colours of the spectrum. NO light is reflected into our eye. The snooker ball appears black. © Boardworks Ltd 2003

White objects Why does a white snooker ball look white in white light? The snooker ball doesn’t absorb any of the colours of the spectrum. The whole spectrum of light is reflected into our eye. The snooker ball appears white. © Boardworks Ltd 2003

Magenta objects Why does a magenta ball look magenta in white light? The ball absorbs all the colours of the spectrum EXCEPT red and blue, red and blue light is reflected into our eye. The ball appears to be magenta, a mixture of red and blue light. © Boardworks Ltd 2003

Look at the clothes below. What colour light is reflected by these clothes? © Boardworks Ltd 2003

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. © Boardworks Ltd 2003

Filters let certain colours of light pass through, but absorb all other colours. Using different coloured filters placed in front of your eye, look around the classroom and see what effect they have on your vision. Object filter © Boardworks Ltd 2003

Red, blue and green filters Red filters absorb all colours…. … apart from red light Blue filters absorb all colours…. … apart from blue light Green filters absorb all colours…. … apart from green light © Boardworks Ltd 2003

Magenta, cyan and yellow filters Magenta filters absorb all colours…. … apart from red and blue light Cyan filters absorb all colours…. … apart from blue and green light Yellow filters absorb all colours…. … apart from red and green light © Boardworks Ltd 2003

But why do colours look different in different coloured light? Lets start with the example of a red ball in red light. The red light shines on the ball. The red ball reflects red light and so appears red. © Boardworks Ltd 2003

What about the red ball in green light? The green light shines on the ball. The So green what colour ball only does reflects a green light ball appear so it absorbs in blue light? the red light and reflects nothing. Therefore it appears black. The red ball only reflects red light so it absorbs the green light and reflects nothing. Because it doesn’t reflect any type of light it appears black. © Boardworks Ltd 2003

But what if the filter you are using lets through more than one type of light. For example what will our red ball look like in magenta light. The magenta light shines on the ball. Remember that magenta is a mixture of blue and red light The ball reflects only red light. Therefore it absorbs the blue light and reflects the red light. It will appear to be red. © Boardworks Ltd 2003

Over the next two slides you will be shown the same girl as in the previous example. However, she will be standing in a different coloured light each time. The colour of this light is written at the top of the slide. Your task is to drag the correct shirt and trousers onto the girl to represent what those clothes would look like in this coloured light. © Boardworks Ltd 2003

Complete the table below by adding in the colour that each object would appear to be in the conditions listed. Object (Colour) Colour Filter Appearance red ball red red ball blue black blue book green black blue book magenta green apple cyan blue green apple magenta black red and blue tie red and black © Boardworks Ltd 2003

Actvity Flag colours For the flag shown, draw what it will look like in: a) Red light b) Green light c) Blue light © Boardworks Ltd 2003

Multiple Choice Questions © Boardworks Ltd 2003

Which of the following is not a light source? A. The Sun B. A

Which of the following is not seen by reflected light? A. Your hand B. Jupiter C. Light bulb D. The Moon © Boardworks Ltd 2003

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

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 © Boardworks Ltd 2003

If a ray of light moves from a more dense medium to a less dense medium at an angle to the normal what happens? A. It continues with no change of direction B. It bends towards the normal C. It bends away from the normal D. It stops © Boardworks Ltd 2003

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

$Which colour below is refracted (bent) the least by a glass prism? A. Red$

Which colour below is refracted (bent) the least by a glass prism? A. Red B. Orange C. Yellow D. Green © Boardworks Ltd 2003

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

Which two primary colours make magenta? A. Red and cyan B. Red and yellow C. Red and blue D. Blue and violet © Boardworks Ltd 2003

If white light passed through a magenta filter and then a blue filter, what colour would emerge? A. Red B. Red and blue C. Blue D. Black © Boardworks Ltd 2003