PHY ICS - The Institute of Physics in Ireland

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light 41 How the eye works: introduction Bulgaria How the different parts of the eye and brain contribute to vision You will need... ✔ an overhead projector and screen ✔ small circles of red and green filter (diameter ~ 2 cm) ✔ green and red filters (106 and 139 from suppliers of filters for stage lighting) ✔ an image from the Internet (www. ebaumsworld.com/ manillus.html) ✔ for each person, a square of black card ( ~ 4 × 4 cm), a pin, a rubber band, two matches and a long measuring tape ✔ some plain white paper ✔ a thick black marker pen ✔ an optician’s Snellan chart Background The following experiments are equally relevant to physics students studying the refraction of light by lenses and to biology students studying vision. They have the enormous dual advantages of involving students actively in the experiments yet requiring only very simple equipment. The nine experiments show in turn how the following parts of the visual system contribute to human vision: the aqueous humour, the pupil, the lens, the retina, the rods, the cones and the brain. The retina is the layer of cells in the eye that are sensitive to light, including the rods (black-and-white vision) and the cones (colour vision). The fovea is the place on the retina where the cones are concentrated and where the image is focused for the best vision when you look directly at something. The brain also plays a vital role in the amazing sense of vision. PHYSICS ON STAGE 3
42 light How the eye works, continued... Pupil: why have a narrow entrance to the eye? Follow these steps 1 Make a small pinhole at the centre of the card. 2 Without the card, focus on an object at the front of the room and hold the pin in front of you at arm’s length. 3 Still focusing on the distant object, bring the pin closer and closer until it goes out of focus. 4 Note how far away the pin is when this happens. 5 Now focus on the same distant object as before but view it through the hole in the card. 6 Move the pin closer and closer as before, noting the distance at which it becomes out of focus. So what happened? The pin remains in focus much closer to the eye when you look through a small hole. A much greater depth of field is in focus when the entrance to the eye is smaller. The small entrance to the eye means that the light coming from both objects (the distant object and the pin) is much more similar, so the depth of focus is greater (see figure). PHYSICS ON STAGE 3
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PHY ICS on Stage 2 & 3 on Stage 2 &
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Foreword It is a pleasure to introd
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PHYSICS ON P R ESTAGE S S U R 2E Ph
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1 2 3 4 5 6 7 8 CP OR NE ST SE UN R
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I N T R O D U C T I O N v The Irish
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P R E S S U R E Demonstration of at
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Bernoulli effect 1: ping-pong ball
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The Bernoulli effect 3: the slipstr
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The atmospheric karate chop IRELAND
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P R E S S U R E 9 ‘Heron’s Foun
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Newton’s third law For every acti
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To show air has mass SPAIN: ‘Teac
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Surface tension - ‘water-knot’
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The paperclip and the falling teacu
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The inclined plane This apparatus c
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F O R C E S To show that vertical a
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D E N S I T Y To demonstrate the ef
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The sinking orange IRELAND: The ora
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The boat and ball IRELAND: The boat
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Submarine model to demonstrate dens
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The balloon that doesn’t burst SP
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WAVES & SOUND Jenga Blocks: to show
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To show sound is a waveform GREECE:
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Diffraction using fingers IRELAND:
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EASY COLOUR 2: Colour mixing - all
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L I G H T EASY COLOUR 4. Red light
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Estimating the speed of light from
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Geometric optics with a laser point
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E L E C T R I C I T Y & M A G N E T
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M I S C E L L A N E O U S Gedanken
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Can you pick up a cube of ice with
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Electroless plating Background Elec
Page 67 and 68: M I S C E L L A N E O U S Some exce
Page 69 and 70: Answers to thought experiments with
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Page 73 and 74: PHYSICS ON STAGE 3 Team and contrib
Page 75 and 76: PHYSICS ON STAGE 3: The conference
Page 77 and 78: PHYSICS ON STAGE 3: Acknowledgement
Page 79 and 80: 2 pressure Can you feel the force?
Page 81 and 82: 4 pressure Pressure with a differen
Page 83 and 84: 6 forces Water rocket Austria Break
Page 85 and 86: 8 forces Has Newton’s Law gone wr
Page 87 and 88: 10 forces Can you balance six nails
Page 89 and 90: 12 forces Anyone for tennis? Belgiu
Page 91 and 92: 14 forces Which syringe is easiest
Page 93 and 94: 16 forces Soap bubbles and films: 2
Page 95 and 96: 18 forces Moments on a wheel The Cz
Page 97 and 98: 20 density The mystery of the vanis
Page 99 and 100: 22 heat Making a turbine from a pla
Page 101 and 102: 24 waves & sound Standing waves in
Page 103 and 104: 26 waves & sound Kundt’s tube Lux
Page 105 and 106: 28 light Which one is the tonic wat
Page 107 and 108: 30 light Real depth and apparent de
Page 109 and 110: 32 light Disappearing crystals Irel
Page 111 and 112: 34 light How to make a wooden mirro
Page 113 and 114: 36 light Investigating colour Irela
Page 115 and 116: 38 light Hot headlamps The Czech Re
Page 117: 40 light Words in a tube The Czech
Page 121 and 122: 44 light How the eye works, continu
Page 123 and 124: 46 light How the eye works, continu
Page 125 and 126: 48 electricity & magnetism The elec
Page 127 and 128: 50 electricity & magnetism Seeing a
Page 129 and 130: 52 electricity & magnetism The Darl
Page 131 and 132: 54 miscellaneous Bottle race Belgiu
Page 133: 56 miscellaneous The Coriolis effec
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PHY ICS - The Institute of Physics in Ireland

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