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INTRODUCTION TO LIGHT

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REVIEW We can see our surroundings because light bounces off of objects and into our eyes.

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ELECTROMAGNETIC SPECTRUM The electromagnetic spectrum is made up of different sized wavelengths. Humans are only able to see the visible portion of the electromagnetic spectrum.

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The shortest wavelengths are gamma waves. The longest wavelengths are radio waves. All of the different wavelengths combine together to form a continuous spectrum.

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LIGHT FROM THE SUN The Sun is the most abundant source of light. When energetic hydrogen atoms at the center of the sun collide, they sometimes combine or fuse to form helium. These reactions are called fusion reactions.

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LIGHT FROM THE SUN When the gases on the outer layer of the sun release some of their excess fusion energy, the energy is emitted as sunlight.

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LIGHT FROM INCANDESCENCE Incandescence: light that is emitted by a very hot object. Incandescent light bulb: an electrical current runs through a thin tungsten wire. The electrical energy generates heat, which then excites the atoms in the wire. As the excited atoms release their energy they emit light.

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LIGHT FROM INCANDESCENCE 5% of electrical energy is used to generate light, 95% is lost as heat. Incandescent light bulbs are inefficient.

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LIGHT FROM ELECTRIC DISCHARGE An electric current is passed through a gas, the electric energy excites the atoms of the gas and as the gas atoms release their energy they emit light.

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LIGHT FROM ELECTRIC DISCHARGE Most commonly found in streetlights, the characteristic yellow light comes from the excited atoms of sodium vapour.

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FLUORESCENCE Fluorescent bulb: a tube with an electrode at each end is filled with mercury vapour and the inside walls are coated with a powdery substance called phosphor.

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FLUORESCENCE An electric current excites the mercury vapour, which emits ultraviolet light (not visible). The phosphor absorbs the UV light and then emits energy in the form of visible light.

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WHITE LIGHT Most light sources emit white light. White light is a combination of all the colours of the rainbow.

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WHITE LIGHT IN A PRISM When white light passes through a prism it is divided into all of the colours of the rainbow.

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QUICK CLIP Bill Nye: Light and Colour introduction Bill Nye: Light and Colour introduction

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ANSWERS White light is (K) An orange (D) We dont see things (J) When white light goes into a prism (A) A green apple (G) Chemicals on the skin of fruits and vegetables (B) Where do all the other colours go? (C) A black cloth is warm because (F) A white cloth is not warm because (H) Blue paint (I) Red clothing (E) A. It breaks into all the colours of the rainbow. B. absorb and reflect different colours. C. They are absorbed and turned into heat. D. absorbs all colours EXCEPT orange. E. absorbs all colours and reflects red. F. it is absorbing almost all colours and turning them into heat. G. reflects green and absorbs all other colours. H. It is reflecting almost all of the colours. I. absorbs most colours and reflects blue. J. we see light bouncing off of things. K. a mixture of all the colours of the rainbow.

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COLOUR ADDITION The primary colours of light are red, blue, and green. The secondary colours of light are yellow, magenta, and cyan. When red, blue, and green light are overlapped, the result is white light. R + G = Y R + B = M B + G = C R + B + G = W

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COLOUR SUBTRACTION Consider a white light shining on a shirt that absorbs only blue light and reflects all other colours The shirt is absorbing blue and reflecting red and green From the theory of colour addition we know that red + green = yellow The shirt will appear yellow.

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COLOUR SUBTRACTION The same shirt (still absorbing only blue) has a cyan light shone on it (Hint: C = G + B ) The shirt will appear green.

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INTRODUCTION TO HOW WE SEE The parts of the eye that allows us to detect colour and movement are called rods and cones.

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RODS Rods are most sensitive to dark changes, shape and movement. They are NOT effective at detecting colour.

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CONES Cones are used for colour vision and are wavelength specific

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CONES There are three types of cones: Red ConesGreen ConesBlue Cones Detects long wavelengths (i.e. red, orange, yellow) Detects medium wavelengths (i.e. yellow, green, blue) Detects short wavelengths (i.e. blue, indigo, violet)

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COLOUR BLINDNESS What does it mean if someone is colour blind? A person is colour blind when one or more types of their cones are partially or completely deficient. ProtanomalyDichromasyProtanopia Referred to as red- weakness. A protanomalous viewer has trouble detecting the saturation of red as well as the brightness of red. A deficiency of red cones No perceptible difference between red, orange, yellow, and green. All of these colours appear to be the same. A deficiency of red cones and green cones. The brightness of red, orange, and yellow are greatly reduced compared to normal. Protanopes often confuse red to be black or grey. A deficiency of red cones

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PROTANOMALY Notice: o The colour normal berries appear brighter than colour deficient. o Purple is made of blue and red. The colour deficient viewer is unable to see the red component of the purple berries, so the berries appear blue

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WHAT DO DOGS SEE? While humans have three types of cones, dogs only have two types of cones. Research shows that dogs are missing the long-wavelength cones (the cones that detect red, orange and some yellow).

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Dogs also have fewer cones than humans so their vision is less rich and intense as a humans vision

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COLOUR VISION FACTS The gene that encodes the red cones lies on the X chromosome. Females have two X chromosomes while males only have one X chromosome. For this reason, women see varying shades of red while most men see only fire engine red.

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COLOUR VISION FACTS Bees and butterflies have better colour vision than humans. Both insects are able to see colours that humans cannot see. Their colour vision extends into the ultraviolet region. The ultraviolet wavelengths (which are invisible to humans) reveal patterns on flowers that guide bees and butterflies to the centers of nutritious flowers.