Presentation Transcript

1. Physics

   Light and Geometric Optics
2. What is Light? If you had an alien friend come visit you on Earth, how would you describe light? Explain light? What is light?!
3. What is Light? Light is a form of energy that is visible to the human eye. It can be described: As electromagnetic waves As particles of light called photons
4. Light is a wave that travels in a straight line… SAY WHAT?! Rectilinear Propagation SAY THAT AGAIN?! We only see objects if light reflects off of it. We can only see the light if there are dust or smoke particles in the air. (i.e. laser show) We see the absence of light as shadows.
5. Rectilinear Propagation Why do shadows form? Shadow simulator Why do eclipses occur? Both of these phenomena are a result of rectilinear propagation... The simple fact that light must always travel in straight lines.
6. Shadows and Eclipses Solar eclipses occur when the moon comes directly between the sun and the Earth. The region of the umbra (the darkest shadow) is left in total darkness.
7. Light Waves Light waves contain both electric and magnetic fields Because light has both electric and magnetic fields, it is also referred to as electromagnetic radiation Light = energy = waves = light waves = Electric & magnetic waves = Electromagnetic waves Light = Electromagnetic radiation Through space! What does it Travel through?
8. Properties of Waves Crest: highest point on a wave Trough: lowest point on a wave Rest Position: level that there are no waves Amplitude: height from the rest position to the highest point on a crest or lowest point on a trough. Wavelength( λ- lambda): distance from one place in a wave to the next similar. Ex: Distance from crest to crest. Frequency( ƒ ): the rate of repetition of a wave; measured in hertz (Hz) = cycles per second. Ex: 3 cycles / second Cycle: one full wavelength represents one complete cycle
9. Draw the wave and label Crest? Trough? Wavelength? Amplitude? Rest Position?
10. Understanding the Electromagnetic Spectrum Imagine bouncing a ball in a box… Describe and draw the following if A ball is thrown hard A ball is thrown softy Energy: Frequency:  :
11. Understanding the Electromagnetic Spectrum Which wave has more energy?
12. Electromagnetic Waves From the Sun Which can we see? Infrared (heat) 2. Which can we feel?  Visible Light (ROYGBIV) Which is invisible to us? Ultraviolet (UV) Which colours have the least energy? The most energy? Which is dangerous?
13. UVA and UVB rays can penetrate our skin (short waves, high energy) UVC rays are absorbed by the atmosphere before they reach the ground (waves even shorter, higher energy) Summer Months - UV is highest Midday - UV highest at 10 AM and 4 PM Snow, Sand and Water - Reflection enhances UV Electromagnetic Waves From the Sun Best ways to avoid skin cancer: Stay out of the sun/ tanning beds Block UVA/UVB No smoking # way of getting wrinkles= tanning
14. Components of Visible Light Wavelengths of the light we can see is =10-6 m (400-700 billionths of a meter) “Visible light” is made up of ROYGBIV – colours of the rainbow Visible white light is filled with colour! ROYGBIV
15. Colours and Visible Light Visible light waves have different sizes The varying wavelength’s (’s)gives us ROYGBIV Which colours have the least energy? The most energy?
16. Carry information with different combinations of amplitude, frequency and wavelength (AM radio, FM radio) TV, cell phones, satellites, broadban internet, MRI scans Penetrate human tissue but not bones. Used for medical imaging, airport security and for photo’s of the insides of pipes, engines and other machines. The Electromagnetic Spectrum Heat that we feel! Used in burglar alarms, motion sensors, night vision goggles. Electro- magnetic Radiation All forms of energy are organized & classified in this spectrum by their size of wavelength ~ width of the wave Longest – Radio waves Shortest – Gamma Rays Where is light in the spectrum? Use to heat food by making water particles in food vibrate. Radar – uses microwaves to measure speeds RADARSAT – maps Earth’s surface by radar. Produced by neutron stars and black holes in galaxies. Can penetrate tissues. Used to sterilize medical equipment, to kill cancerous cells. Has been used to disinfect drinking water, waste water, and in DNA analysis.
17. Various Types of Light Emissions 1) Luminescence is light produced using energy sources including or excluding heat; can occur cooler temperatures Electrons of atoms become excited & unstable when it absorbs energy The electron will return to normal when it releases this “extra” energy as light (photon).
18. 2) Chemiluminescence Light energy released from a chemical reaction without the involvement of heat or a flame (a cold system) Ex: Glow-sticks, bioluminescence, luminol (a chemical used in crime scenes – it glows when it reacts with iron in blood.)
19. 3) Bioluminescence Light is released by a chemical reaction; occurs naturally in plants or animals. 90% of sea creatures are bioluminescent. Some fish produce their own light others have bacteria do it. Deep sea creatures make their own light to Find prey, attract predators (black sea dragon, angler fish) Scare predators Attract mates Camouflage Fireflies – attract mates by flashing lights in specific patterns Others – Algae, crustaceans, earthworms, fungi
20. 4) Incandescence Light energy produced by heated objects substance becomes hot and glows Ex: incandescence light bulbs – filament inside that heats up when current flows through it and emits light energy. Only 5% of energy is converted to light 95% is released as heat
21. 5) Fluorescence A light emitted by substances when they are exposed to EM radiation Fluorescent light bulb a glass bulb filled with gas (mercury vapour). The gas particles get energized when electricity flows through. Inside of bulb is coated with white powder called a phosphor Phosphor – glows when exposed to energized particles. 80% of energy is converted to heat, 20% to light Contains more toxins then incandescent bulbs and require careful cleanup if broken Other fluorescence – some rocks
22. 6) Phosphorescence The ability to store energy from a light source, and then emit it slowly over a long period of time. Ex: Glow in the Dark material The energy gets used up but can be re-energized by further exposure to a light source. Ex: Painted with phosphorescent ink
23. 7) Triboluminescence Light produced by friction Eating lifesavers in the dark (crushing wintergreen candy) Breaking apart sugar crystals Rubbing a diamond
24. 8) Electric Discharge When an electric current passes through gases, light is often produced Ex: Lightning, lamps
25. 9) Light-Emitting Diode LED Electroluminescence – solid device that transforms electric energy directly into light energy LED’s Made out of a semi-conductor – material that emits light when a small amount of current passes through it. Use small amounts of electricity Last longer then other bulbs Light up much faster Used for, traffic lights, bilboards, x-mass lights, handheld displays, brake lights
26. 10) OLED, Plasma, Liquid Crystal OLED – Organic light-emitting display Light source made of thin layers of organic molecules that use electric current to produce light Use less energy, thinner, lighter, brighter, flexible Can be rolled, embedded into clothes Expensive to produce, can be damaged by water Plasma Displays Each colour is a tiny fluorescent light, different phosphors used to make red, green, blue light. Brighter images then LCD, more energy to operate Liquid Crystal Displays - LCD A solid that can change the orientation of its molecules like a liquid when electricity is applied Laptops, digital watches, cell-phones, iPods use LCD’s
27. Where does Light Come From? Comes from an energy source… Light can move through a Vacuum, & through different mediums How fast does light travel? Speed of Light = 299 792 458 m / s For simplicity, we will use: Speed of light = 3.0 x 108 m/s Light moves 300 000 000 meters every second in a vacuum Which comes first, lightning or thunder? Sound is a wave too! Speed of Sound= 340 m/s Sound moves slower than light!
28. How Does the Ball Behave? How would the ball behave…? Imagine throwing a ball through the air… Imagine throwing a ball at a brick wall… Imagine throwing a ball under water…
29. How does Light Behave? The ball & light behave similarily: Light travels the fastest when… Light travels at differing speeds when… Light bounces back when… There’s no matter…vacuum It passes through matter…different mediums…  REFRACTION (light bending) It cannot penetrate a surface REFLECTION (light scattering)
30. When light hits an object, it can be… Transmitted- pass through the object Refracted- light bends as it is absorbed by the object 3. Reflected- light is scattered away from the object Rays – represent light as a straight line
31. Material classification by how they transmit light Transparent Transmit light freely Can see through it clearly Translucent Transmit some light but not enough to see through clearly Opaque Absorb and reflect light but do not transmit it
32. Law of Reflection Reflection from a plane mirror: Normal Reflected ray Incident ray Angle of reflection (θr) Angle of incidence (θi) Mirror “Normal line” is perpendicular (90) to the surface Mirror
33. The Law of Reflection Angle of incidence(θi)= Angle of reflection(θr) In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!! Greek letter, theta (θ). Common symbol for angle. Angle (θ)is measured FROM the NORMAL to the ray
34. Ray Diagrams Ray Model of Light  Allows us to trace the path that light travels Why? So we can predict the location of the reflected image of an object Note: The rays (incident rayand the reflected ray) are drawn as straight arrows
35. Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear or regular reflection. Rough, uneven surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions
36. Seeing Reflected Images- Ray Diagrams “Plane mirrors produce upright virtual images with lateral inversion” Draw a solid line perpendicular from the object to the mirror. Extend the line (dashed) an equal distance behind the mirror
37. Seeing Reflected Images- Ray Diagrams “Plane mirrors produce upright virtual images with lateral inversion” Why virtual? Draw a solid line perpendicular from the object to the mirror. Extend the line (dashed) an equal distance behind the mirror
38. Seeing Reflected Images- Ray Diagrams “Plane mirrors produce upright virtual images with lateral inversion” 3. Draw a normal halfway between the object and eye.
39. Seeing Reflected Images- Ray Diagrams “Plane mirrors produce upright virtual images with lateral inversion” 4. Draw solid rays from the object, reflecting on the mirror and to the eye. θi= θr
40. Seeing Reflected Images- Ray Diagrams “Plane mirrors produce upright virtual images with lateral inversion” 5. Extend the reflected line (dashed) backwards behind the mirror until it hits the other line. 6. Repeat for all other distinctive parts of the object.
41. Seeing Reflected Images- Ray Diagrams
42. Now YOU try! Image Characteristics S (size)- same, smaller, or larger A (attitude)- same, right side up Inverted (upsided down) L (location)- same, above, or below T (type)- real or virtual
43. Using mirrors Two examples: 2) A car headlight 1) A periscope
44. Ray Diagrams Continued…. Concave Mirrors (converging) - collects light rays & brings them to a single point. - Produces larger images Convex Mirrors (diverging) - designed to spread light rays out - Produce smaller images What if the mirror is curved? Which is Concave? Convex?
45. Applications to Concave Mirrors Concave Mirrors - used in flashlights, telescopes, cosmetic mirrors, headlights of a car, dentist lights - concentrates light to one particular spot.
46. Applications for Convex Mirrors Convex Mirrors: - used in security mirrors at variety stores, side-view and rear view mirrors in a car Allows you to view a larger region from one location
47. Terminology for Curved Mirrors We will first use a Concave Mirror to label these terms.. Vertex – midpoint of the curved mirror Principal Axis – a straight line that passes through the vertex (symmetrical & perpendicular) Center of Curvature (C) – think of it as the center of a circle; it lies on the principal axis Radius of Curvature (R) – distance from the vertex to the center of curvature
48. Terminology for Curved Mirrors Focus or Focal Point (F ) – the half way point from the center of curvature (C ) to the vertex; this is where reflected rays* pass through and converge *Reflected rays pass the focal point when incident rays are parallel to the principal axis Focal length (f ) – the distance from the vertex to the focus or focal point (F ) From the focal point to the vertex has a length of… f. What is the length from C to the vertex?
49. Diagram for Curved Mirrors We applied the new terminology for a Concave Mirror. Now, YOU try labelling the terms for a Convex Mirror! Which way is convex?! Remember : * Principal Axis (PA) * Vertex * Center of Curvature (C) * Radius of Curvature (R) * Focus or Focal Point (F) * Focal Length (f )
50. Ray Diagrams for Concave Mirrors Depending on where the object is located on the principal axis, ray diagrams are used to determine… S A L T S = the SIZE of the Reflected Image (smaller, larger, or the same as the object) A = the ATTITUDE of the RI (right-side up or upside down L = the LOCATIONof the reflected image (RI) T = the TYPE (real or virtual) We will look at 5 cases…
51. Drawing Ray Diagrams for Concaved Mirrors 1st incident ray is drawn parallel to the principal axis, starting from the top of the object to the mirror (blue). Can you predict and draw the reflected ray (red)? 2nd incident ray is drawn from the top of the object through the focal point to the mirror (blue) Predict and draw the reflected ray (red). The image is formed where the rays intersect. This intersection point on the image is the same point that was on the object.
52. 1. Object is Located Beyond the Center of Curvature 1st incident ray is drawn parallel to the principal axis, starting from the top of the object to the mirror (blue). Can you predict and draw the reflected ray (red)? 2nd incident ray is drawn from the top of the object through the focal point to the mirror (blue) Predict and draw the reflected ray (red). The image is formed where the rays intersect. This intersection point on the image is the same point that was on the object. Image Characteristics S- A- L- T- Any Incident Rays travelling parallel to the principal axis will reflect and pass through the focal point Any Incident Rays passing through the FOCAL POINT will reflect and travel parallel to the principal axis General Conclusion An object located beyond the Center of Curvature will reflect an image that is: located between C and F Is real, smaller and upside down
53. 2. Object is Located at the Center of Curvature Same as previous slide… 1st incident ray travels parallel to principal axis from the top of object towards the mirror (blue) Predict & Draw reflected ray (red) 2nd incident ray travels from the top of the object through the focal point to the mirror (blue) Predict & Draw reflected ray (red). The image is formed where the rays intersect. Image Characteristics S- A- L- T- General Conclusion An object located at the Center of Curvature will reflect an image that is: Also located at C Is real, same size and upside down What do you notice about the image?
54. 3. Object is Located Between the Center of Curvature and Focal Point Same as previous slide… 1st incident ray travels parallel to principal axis from the top of object towards the mirror (blue) Predict & Draw reflected ray (red) 2nd incident ray travels from the top of the object through the focal point to the mirror (blue) Predict & Draw reflected ray (red). The image is formed where the rays intersect. Image Characteristics S- A- L- T- General Conclusion An object located between the Center of Curvature and the Focal Point will reflect an image that is: located beyond C Is real, larger size and upside down
55. 4. Object is Located Between the Focal Point and Mirror Same as previous slides… The 1st ray is drawn parallel to the principal axis from the top of the object to the mirror (red) Can you predict and draw the reflected ray? The 2nd ray is drawn from the top of the object through the focal point to the mirror (blue) Predict and draw the reflected ray. The image is formed where the rays intersect. This point on the image is the same point that was on the object Image Characteristics S- A- L- T- General Conclusion An object that is located between the Focal point and the mirror will reflect an image that is: located behind the mirror Is right side up, larger and is virtual
56. 5. Image Is Located at the Focal Point No SALT 1st incident ray travels parallel to principal axis from the top of object towards the mirror (blue) Predict & Draw reflected ray (red) 2nd incident ray travels from the top of the object through the focal point to the mirror (blue) Predict & Draw reflected ray (red). What do you notice…?
57. Ray Diagrams for Convex Mirrors What does a Convex Mirror look like again ? Surface curving outwards Unlike the concave mirror with 5 different cases, the convex mirror has only one case. SALT is still used to determine the image’s characteristics: S- image is smaller than the object A- image is in the upright position L- image is located behind the convex mirror T- virtual image The object’s distance to the mirror doesn’t change the image’s SALT
58. Calculations for Curved Mirrors & Thin Lenses To calculate object or image dimensions mathematically we use:  Thin Lens Equation (Gaussian Lens Formula) Magnification Equation Measure of how much Larger or smaller the object looks M>1 or < -1 () 1 > M > -1 ()
59. Ex 1: Find the image position and magnification for a convex mirror with a focal length 20cm, with a candle 5.0cm away from the vertex. Ex 2: A diverging lens of focal length 200cm is used to correct a person’s nearsightedness. Find the image position of an object 3.00m away.
60. What type of mirrors? Negatives: (same for mirrors and lenses) Focal point -f -‘ve diverging mirror/lens Magnification -m -‘ve inverted image Image Distance -di -‘ve virtual image (in front of lens of behind mirror)
61. Light Refraction What happens when light rays do NOT reflect? In a vacuum, light travels in a straight line … However, if light rays encounter a medium (matter), such as water, then what happens?…. Light bends as it passes through water! The straight-line path of light CHANGES!
62. Light Refraction LR are light rays bending when it passes through different mediums (light changes its speed, either slowing down or speeding up Ex: light passes from air to water & vice versa The more the light ray slows down, the more the light is refracted (bends more). Light only refracts at the boundary of the two different mediums
63. Index of Refraction I of R is a number, a value given to a medium… - The amount by which a medium decreases the speed of light is indicated by this value I of R The larger the I of R for that medium, the more it decreases the speed of light. Ex: Diamonds slow down (bend) light more than water, thus diamonds have a greater index of refraction than water Certain materials bend light in similar ways…thus they have similar indexes of refraction
64. Refracted Index Light travelling in a vacuum – Refracted Index is 1.00 Light travelling in air – RI is 1.0003 ~ 1.00 Light travelling in water – RI is 1.33 How are these values obtained? - Index of Refraction of Material is found by comparing speeds of light in their respective mediums Refracted Index (n) = speed of light in vacuum (c) speed of light in medium (v)
65. RI and θ of Refraction Snell’s Law Angle of Refraction: amount of light bending Snell’s Law: When light travels from air (low RI) into water (higher RI), it bends TOWARDS the normal, θi > θr (speed ) RI = θ Refraction (closer to normal) When light travels from water (denser, higher RI) into air (less dense, lower RI), refracted ray bends AWAY from the normal (speed ) - The more the medium slows down the light, the greater the difference between θi and θr
66. Total Internal Reflection (TIR) = Trapped Light LR is light bending when traveling through different mediums… As the angle of θiincreases to the normal, θr increases too. At a certain angle critical angle ( θc ), refracted rays will not leave the medium; instead travel along the boundary line. Increase θieven more & the ray will no longer refract, but only reflect rays. (trapped within the medium) TIR – when θi>θc, light rays no longer refract, but reflect and stays within the medium
67. Dispersion Special type of refraction in diamonds, rain drops, and prisms They can be colorless or show all the colours of the rainbow…dispersion is when the refraction of white light is separated into its colours Each colour travels a slightly different speed when it goes through the glass prism. Violet light slows down more then red. Ex. Rainbow: light passes through rain drops and some light is reflected BUT some light is refracted as well Light is refracted twice, when light enters and when light leaves….both separate light into its colours
68. The Physics of Bling 1. The index of refraction of a diamond is 2.4 One of the highest for a clear substance Explains why diamonds are bling 2. The angle of incidence of diamonds should be 24.5…making it glitter
69. Optical Illusions: Both Reflection and/or Refraction Desert Mirages An image of a distant object produced as light refracts through air of different densities Light is internally reflected and refracted as it passes through the progressively hot air lying near the ground, light is totally internally reflected There appears to be a lake in the distance, but this is actually the image of the sky produced by light bending near the hot air near the ground… End of the Rainbow Location of rainbows are relative to YOU, the SUN, and the RAIN
70. Optical Illusions: Both Reflection and/or Refraction 3. Shimmering The shimmering image of the moon on a lake at night. Light is refracted when passing through air of different temperatures. Air above the lake is much warmer. Light travels through cooler air slowly and bends toward normal. Continues through warmer layer bending further from the normal. Eventually TIR occurs and multiple virtual images of the moon on the lake result. 4. Apparent Depth The depth that an object appears to be due to the refraction of light in a transparent medium. The object under water always appears to be nearer to the surface then it actually is.
71. Optical Illusions: Both Reflection and/or Refraction 5. The “Flattened” Sun Sun appears flattened during sunrise and sunset? This is due to the common phenomenon of atmospheric refraction.
72. Applications of TIR Fiber Optics: Light travels in a straight line, BUT what if you want light to bend? Optical fibre: thin transparent glass tube that transmit light around corners…the light does not escape because of TIR Fiber Optics are used to transmit telephone and internet communications A optical fibre cable is made of 1000’s of optical fibres packed together
73. Lenses
74. There are two types of lenses: Converging (Convex) Diverging (Concave) Types of Lenses
75. Converging Lenses …have a positive focal length (f>0) Cause rays to intersect at the focal point Used for magnifying glasses, microscopes, telescopes and reading glasses… REAL IMAGE (if on the same side as the viewer)…3 out of 5
76. Diverging Lenses …have a negative focal length (f<0) Cause rays to spread out as if they came from a focal point…IMAGE is on same side as object… VIRTUAL IMAGE (always) Used for distance glasses.
77. Optical Centre, O Focal length, f Focal point, F’ Focal point, F Lens Terminology Principal Axis 2F’ 2F F’= secondary focus F’ is on the opposite side for diverging lenses
78. If the incident ray… then the refracted ray… Diagram is parallel to the principal axis, comes through the focus, comes through the optical centre, Ray Rules–Converging Lens Goes through F Emerges parallel to the principal axis Is not refracted.
79. Forming an Image Draw a ray from the object to the lens (use one of the special rays described). From the same position on the object, draw another special ray. The image is located where the refracted rays meet.
80. Converging Lens- 5 Cases 1. Beyond 2F’ 2. Object at 2F’
81. Converging Lens- 5 Cases 4. At F’ 3. Between 2F’ and F’
82. Converging Lens- 5 Cases Between F’ and O
83. Example Find the image for the following case:
84. Five Case Scenarios for Converging Lenses Between f and 2f inverted smaller real At 2f inverted same size real Beyond 2f inverted larger real No Image Formed Behind object upright larger virtual
85. If the incident ray… then the refracted ray… Diagram is parallel to the principal axis, Is aimed at the focal point prime, comes through the optical centre, Ray Rules– Diverging Lens Emerges as if it came from F. Emerges parallel to the principal axis Is not refracted.
86. One Case Scenario for Diverging Lenses With a diverging lens, the image is always: Between F and O Upright Smaller Virtual Lens Applet
87. The Eye What is the function of? Cornea Aqueous and vitreous humour Lens Ciliary muscle Retina Choroid Sclera Optic nerve blind spot Fovea Iris What parts of the eye are directly related to the unit?
88. Vision Conditions Normal Vision: focus point is at the back of the retina Myopia (near-sightedness): distant objects are blurry, 1/3 of people, longer eye ball Hyperopia (far- sightedness) close objects are blurry, shorter eye ball or flat cornea
89. EyeConditionsSummary
90. Vision Conditions Presbyopia: loss of flexibility of eye’s natural lens ~40 years, need bifocals or reading glasses Astigmatism: eye has 2 focal points instead of 1
91. Application of Optics Telescopes Amateur astronomers use reflecting and refracting telescopes A reflecting telescope uses mirrors to focus light from a distant object…how? A refracting telescope uses a lens…how?
92. How does “focusing” work?
93. Unit Review Go back over all worksheets Practice ray diagrams for Plane and curved mirrors, and lenses Practice magnification problems for mirrors and lenses Make unit study notes