Unit 2 Optics concept map Sc.8 Unit 2 Optics Unit 2 Optics Ch.4 Properties of light waves 4.1 Waves Wavelength Frequency Amplitude Crest / Trough 4.2 Visible light Roygbiv Color Refraction Reflection Ch.5 Mirrors and Lenses 4.3 E-M Spectrum Radio,Infrared Visible UV, Xray, Gamma Transparent Translucent Opaque Shadows Ch.6 Eye and Optical instruments Law of reflection Angle of incidence Angle of reflection Normal Law of refraction Angle of refraction Normal Mirage Convex Concave Flat mirrors Im ages Formed Concave Convex Im ages formed Uses Parts of the eye Near-sighted Far-Sighted Blindness Optical instruments Microscopes Telescopes Lasers and fiber optics Light and Optics Topics in this unit: 1) Properties of waves 2) Properties of light and the electro-magnetic sprectrum 3) Colours 4) Refraction & Reflection 5) Human vision and eye defects 6) Optical instruments 4.1 Properties of waves Waves transfer energy Characteristics of waves: Amplitude Crest Trough Frequency Sound waves We hear things when they vibrate. If something vibrates with a high frequency (vibrates very quickly) we say it has a _____ pitch. If something vibrates with a low frequency (vibrates ______) we say it has a ____ pitch. Words – slowly, low, high, quickly Drawing sounds… This sound wave has a _____ frequency: This sound wave has a ___ _frequency: Drawing sounds… This sound wave has a _____ amplitude (loud): This sound wave has a _____ amplitude (quiet): 4.1 Types of waves Two types of waves: Transverse Compression 4.2 – Properties of Light Light travels in straight lines: Laser Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second. Light travels much faster than sound. For example: 1) Thunder and lightning start at the same time, but we will see the lightning first. 2) When a starting pistol is fired we see the smoke first and then hear the bang. Colour White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is “split up” by raindrops. The colours of the rainbow: Red Orange Yellow Green Blue Indigo Violet Rainbows Water drops act like tiny prisms Adding colours White light can be split up to make separate colours. These colours can be added together again. The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding red and green makes yellow Adding blue and green makes cyan (light blue) Adding all three makes white again We see things because they reflect light into our eyes: Homework Seeing colour The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light A white hat would reflect all seven colours: White light 4.2 Properties of Light summary 1) Light travels in straight lines 2) Light travels much faster than sound 3) We see things because they reflect light into our eyes 4) Shadows are formed when light is blocked by an object 4.3 Light and the ElectroMagnetic Spectrum Electro-magnetic energy uses Radio : radio, tv, heat food, MRI, RADAR, telecommunications. Infrared: heat Visible: we can see Ultra-violet: tanning, cancer, fluorescent light X-rays: medicine, dental Gamma: cancer therapy 5.1 Light and Matter Transparent: lets light through freely, ex. glass Translucent: most light gets through; some is scattered, images are blurry, ex. Frosted glass Opaque: no light gets through Shadows Shadows are places where light is “blocked”: Rays of light 5.1 - Reflection Reflection from a mirror: Normal Reflected ray Incident ray Angle of incidence Angle of reflection Mirror The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!! Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions Using mirrors Two examples: 2) A car headlight 1) A periscope Refraction Refraction is when waves speed up or slow down due to travelling in mediums with different densities. In this case the light rays speed up in the air and are bent, causing the fish’s position to change. The two mediums in this example are air and water. Law of refraction When light moves from a more dense medium (water) to a less dense medium (air) it speeds up - away from normal When light moves from a less dense medium (air) to a more dense medium (water) it slows down -toward the normal Refraction can explain a mirage. The mirage is really the sky appearing to be sitting on the road. 5.2 Images formed by mirrors Flat mirrors form images that are: -upright -same size as object -Equal distance behind mirror; where the light rays appear to meet 5.2 Concave mirrors The image depends on where the object is placed. Used in flashlights, shaving mirrors, telescopes 5.2 Convex Mirrors Convex mirror images are upright and smaller than the object. Used as security mirrors and rear-view mirrors. 5.2 Concave lens-Diverges light. Thinner in the middle. Convex lens - focus light Image depends on where the object is compared to the focal length. Upside down, smaller Upside down, larger Upright, larger 6.1 The Eye 6.1 The eye The eye has a number of structures that refract and focus images on the retina including: Cornea Lens Aqueous humor Vitreous humor 6.1 Correcting focus problems Near-sighted: long eyeball Corrected with: concave lens Far-sighted: short eyeball Corrected with: convex lens 6.1 Correcting focus problems Astigmatism Cornea is distorted Laser surgery to reshape the cornea can correct it. Laser eye surgery 6.1 Blindness Causes: Damaged cornea, lens, retina Disease: Cataracts, glaucoma Snow blindness Color blindness 6.2 Extending vision Optical instruments can help us see very small objects - nearby Ex. Microscopes Or Objects very far away. Ex. Telescopes Using lenses & Mirrors 6.2 Eye vs Camera Camera - eye Ccd - retina Lens - lens Shutter - eyelid Diaphragm - iris Focussing ring - muscle 6.2 Lasers Light Amplification by Stimulated Emission of Radiation 6.2 Fiber Optics Transparent glass fibers that transmit light using Total Internal Reflection. Used for medicine, and transmitting telephone, video and internet signals.