Starter Cameras Communications Projectors Illumination How do we use visible light? (you can’t just say ‘to see’!) Cameras Communications Projectors Illumination

What can you remember from Year 8? On your white board, write down the following: 3 primary colours of light Red, Blue, Green What colour do you get if you mix all three colours of light together? White

What can you remember from Year 8? What colour light is created when: red and blue light shine in the same place? Magenta Blue and green light together Cyan Green and red light together Yellow How could you make white light if you already had magenta light? Shine the complementary colour light ( green).

Define wavelength and frequency of different colours of light Learning Objectives By the end of this lesson you should be able to… Define wavelength and frequency of different colours of light Describe why different surfaces appear different colours. Explain how wavelength affects absorption, reflection, refraction etc in different media. Explain effect of viewing objects through filters and why an opaque object has a particular colour

Watch the clips and answer these questions Why does white light split up to form the spectrum? What is different about each colour of light? How do we use the primary colours of light to create images on a large screen? Why is this possible? \\QUARTZ\Media\Videos\Physics\Videos Waves\Visible spectrum.avi http://ed.ted.com/lessons/how-we-see-color-colm-kelleher

Newton’s disc animation Teacher’s Notes Students can make their own Newton’s disc with a paper or card circle (coloured in using the primary colours or the colours of the spectrum) . Using string or a pencil to spin the disc around, get the students to think about the following questions: What do you predict you will see? What did you observe? What does this tell you?

Dispersion

Dispersion In a vacuum all electromagnetic waves travel at the same speed, but when they travel into a denser medium they slow down.

Dispersion The speed an electromagnetic wave travels at through a material varies slightly with the frequency (colour) of the light. Therefore, within a material, different colours of light travel at different speeds.

Dispersion The higher the frequency of the light the more it will slow down when it travels through a material therefore... Red, lower frequency, will be slowed the least, Violet , highest frequency, slowed the most. n = 1.48 n = 1.51

Primary and secondary colours The three primary colours of light (red, green and blue) can be mixed in different amounts to make all other colours. blue magenta cyan red green yellow The colours made by mixing two primary colours are called the secondary colours – magenta, yellow and cyan.

Transparent, Translucent, Opaque Just checking…

Why do objects look different colours? Can you explain why the frog looks blue and black?

Why do objects look different colours? The colour of the object is related to the wavelengths of light that are absorbed (transmitted if transparent like a filter) or reflected from the surface. The frog looks blue where blue light is more strongly reflected from the surface than any other colour.

Can you explain how a filter would work? The red filter absorbs all the colours of light and transmits only the red wavelength. Now explain what the following colours would look like through a red filter: Green grass Yellow daffodil Magenta Foxglove.

Use the filters Investigate what happens to different colour objects when you look through filters. Why do we not get the ‘pure’ results we might expect?

Homework Complete sheet for homework, don’t immediately turn to the internet if you don’t know the answer, have a think first…

Have we understood? Plenary Seeing Colours.pptx Plenary Seeing ColoursAnswers.pptx

Useful slides if needed

Which primary colours?

Mixing coloured light

How do we see different colours?

Using filters of primary colours A filter absorbs some colours of white light and lets other colours through to create coloured light. A red filter absorbs all colours… ROYGBIV …apart from red light. A blue filter absorbs all colours… ROYGBIV …apart from blue light. A green filter absorbs all colours... ROYGBIV …apart from green light.

Using filters of secondary colours A magenta filter absorbs all colours… ROYGBIV …apart from red and blue. A cyan filter absorbs all colours… ROYGBIV …apart from green and blue. A yellow filter absorbs all colours... ROYGBIV …apart from red and green.

Seeing colours in coloured light

How do we see colours in coloured light?

Seeing colours using filters White light Blue light Blue Ball