10.4 Colour! How do these colours make you feel? Colour moods • Different colours can affect how we feel: • RED can make people angry • ORANGE is a happy colour • YELLOW is a cheerful colour • GREEN is calming • BLUE is a cool but restful colour • Do you agree? Write a list of colours at the back of your books and next to them, write what they make you feel.
Learning Outcomes • Today you will: • Draw a diagram to show the different colours that make up white light • Plan and carry out a presentation about how the different theories of what makes up white light
Memorise these. You have 30 seconds. GO! • Today you will: • Draw a diagram to show the different colours that make up white light • Plan and carry out a presentation about how the different theories of what makes up white light
What was Learning Outcome 2? 2. Plan and carry out a presentation about how the different theories of what makes up white light
Lesson Objective To be able to explain how white light can be dispersed into 7 different colours, according to their wavelengths.
Let’s watch a demo. What colour is the light that we see ‘come out’ of a light bulb? What colours do we see in a rainbow?
10.4 Dispersing light Dispersion Breaking up white light You’ve just seen how a prism can break up white light into 7 colours. This breaking up of white light is called dispersion. The prism disperses the light. KEY WORD ALERT!
10.4 Dispersing light Dispersion Colours This breaking up of white light is called dispersion. The prism disperses the light. When white light is broken up like this the 7 colours are always in the same order. top RED ORANGE YELLOW GREEN BLUE INDIGO VIOLET bottom
10.4 Dispersing light ROY GBIV Colours How can you remember the order? There’s the famous spy: ROYGBIV Or a defeated British king: Richard Of York Gained Battle In Vain See if you can think of your own.
10.4 Dispersing light Rainbows Colours You can see the order in this rainbow.
10.4 Dispersing light Wavelengths Why does light disperse like this? Remember that light is a wave. wavelength The size of a wave is measured from one peak to the next and is called its wavelength. KEY WORD ALERT!
10.4 Dispersing light Wavelength and Dispersion Why does light disperse like this? White light is made up of all the colours of the rainbow. Each colour has its own wavelength. Red has the longest and violet has the shortest wavelength. CAN SOMEONE PLEASE SHOW ME WHERE I WOULD MEASURE THE WAVELENGTH ON THESE DIAGRAMS?
10.4 Dispersing light Wavelength and Colour Why does light disperse like this? When light enters a glass prism it slows down. But the shorter wavelengths slow down most and so bend more sharply. Blue is a short wavelength. Red is the longest one.
10.4 Dispersing light Blue Bends Best Why does light disperse like this? As each wavelength, or colour, slows down at a different rate it therefore has a different angle of refraction to the rest. This means the different colours spread out. REMEMBER! Blue bends best. KEY PHRASE ALERT!
10.4 Dispersing light Spectrum of Colour Why does light disperse like this? The shape of the prism means they spread out even more on leaving the prism. You may see a small spectrum with a rectangular glass block but the colours do not spread out as much. KEY WORD ALERT!
IN YOUR BOOK, COPY AND COMPLETE THE DIAGRAM ABOVE TO SHOW WHITE LIGHT DISPERSING INTO IT’S 7 COLOURS. COLOUR IN THE SPECTRUM ON THE RIGHT TO SHOW THE SPECTRUM OF COLOUR. REMEMBER: ROYGBIV!
SWAP BOOKS, LOOK AT THE ANSWER ABOVE, AND GIVE YOUR PARTNER TWO STARS AND A WISH. STARS = WHAT WENT WELL WISH = WHAT THEY COULD IMPROVE FOR NEXT TIME
Let’s watch a demo. So we know how to split white light into it’s seven colours. Can we turn these colours back into white light? How?
10.4 Dispersing light Making white light again Recombining colours When a second prism is added ‘upside down’ the dispersion of the second prism is in the opposite direction to the original dispersion. White light is formed again.
10.4 Dispersing light Making white light again Recombining colours Look carefully. The two triangular prisms form a parallel-sided glass block. We didn’t see dispersion when we passed a ray of light through a rectangular glass block.
10.4 Dispersing light Making white light again Spinning disc The image stays on the retina at the back of the eye for about 1/10 of a second. When the disc spins very fast all the colours of the rainbow appear on the retina together. The colours all combine to form white light.