2 Topic 1 : What is Light? Light The form of energy we can see BBC video What are some natural light sources?Natural light sourcesSunFireStarsGlow-wormsLightningMagmaWhat are some artificial light sources?Artificial light sourcesLight bulbCamerasStovesTelevisions
3 First Basic Principle of Light Light is a form of energy and when it reaches a surface it can be absorbed and transformed into other forms of energySolar cells change light into electricityTrees change sunlight into chemical energySources of Light1. Incandescent Sources https://www.youtube.com/watch?v=YnMP1Uj2nz0An object heated to such a high temperature that it emits visible lightLight bulbsCandle flames2. Fluorescent Sources https://www.youtube.com/watch?v=BNpFoVdI2LYWhen invisible ultraviolet light is absorbed by the particles of an object. The object then emits some of the energy as visible light.Fluorescent light bulbs
4 3. Phosphorescent Sources The emission of light following exposure to and removal of a source of radiation.Inner surface of televisions and computer screensMain difference between phosphorescent and fluorescent is – particles in a fluorescent source release their light immediately4. Chemiluminescent SourcesThe emission of light resulting from chemical action and not involving heatGlow sticks5. Bioluminescent SourcesAn organism that relies on chemical reactions inside its body to produce light https://www.youtube.com/watch?v=9HXXQBz6Vv0Jelly fish https://www.youtube.com/watch?v=7kyP0XsF0zMSquid surf https://www.youtube.com/watch?v=uqJbUKEPgXc
6 The Ray Model of LightThe ray model of light helps you to predict where shadows will form and how large they will beLight travels in straight linesObjects farther away from the light source cast a smaller shadow and objects closer to the light cast a larger shadowThe ray model also helps you understand what happens when light reaches different materialsLight continues in a straight line through transparent materialsLight travels through translucent materials but the light is scattered and images aren’t seen wellLight does not travel through opaque materials and they cast shadows
7 Topic 2 : Reflection Reflection Process when light hits a surface and bounces back off that surfaceAnalyzing ReflectionDraw the picture in figure 3.15 on page 189The ray that comes from the light source and hits the surface is called the incident rayThe ray that bounces off the surface is called the reflected rayThe line that is at a 90 degree angle to the reflecting surface is called the normal lineThe angle between the normal line and the reflected ray is the angle of reflectionThe angle between the normal line and the incident ray is the angle of incidence
8 The Law of ReflectionThe angle of reflection equals the angle of incidenceEx. If the angle of incidence is 60˚ then the angle of reflection is 60˚
9 Forming an imageTwo important facts about how images form are:Light reflects off all parts of an object in all directions. All the rays from the object reflect off the mirror according to the law of reflection. The rays that reach your eye appear to be coming from behind the mirror because your mind knows that light travels in a straight line.Images in a mirror appear to be the same size as the reflected object and come from an equal distance from behind the mirror.To summarize – Objects appear to be behind the mirror and the objects appear to be equal size and from an equal distance behind the mirror.
11 Curved MirrorsConvex MirrorsConvex mirrors bulge outImages in a convex mirror appear smaller and farther awayConvex lenses are used :- in stores for security- side mirrors in carsConcave MirrorsConcave mirrors bulge inImages in concave mirrors appear to be closer than they actually areConcave mirrors are used on side mirrors in cars, these are often labelled – Objects appear closer than they actually are and concave mirrors are also used in shaving / make up mirrors.
12 Rough SurfacesLight reflects off rough surfaces in many different directionsWhen reading something on paper, the white paper reflects light off in all directions...however, the black absorbs the light and doesn’t reflect so therefore you pick up the image of the letters in between the reflected light. This creates letters and images on paper.Using the ReflectionsReflections are used in everyday life in the following ways:Reflectors on bikes so people can see you in the darkReflectors on clothes so you can be seen in the darkLining up a shot while playing poolTraffic signs so we can see them at nightMirrors
13 Review assignment for marks: Topic 1 Review on page 187Questions 1 , 3, 4, 6 and the answer the following:What are the 5 sources of light and give one example of each?Topic 2 Review on page 199Questions 1, 2, 3 and 4 (only drawings 1 and 2 – need protractor for this)
15 Topic 6 : The Source of Colors The SpectrumThe spectrum is the colors that appear when white light is refracted.The seven colors are red, orange, yellow, green, blue, indigo and violet. The memory aid to remember is ROY G BIVSeeing RedAn object is the color of the light that it reflects.Example:A tomato appears red because it reflects red light and absorbs the other colors.White paper reflects all light so it appears white. All the colors combined create white light.Black absorbs all light so it appears black.
16 How we see colorRods are structures that help detect light and cones are structures that help detect colors.Hint...cones start with C and so do colors.Rods and cones are located in the retina.
17 Topic 7 : The Wave Model of Light Looking at WavelengthDefinitions of:Crest – The high parts of a waveTrough – The low parts of a waveWavelength – The distance from crest to crestAmplitude – The height or depth of a wave from rest positionFrequency is the rate at which a wave moves up and down. Frequency is measured in hertz or cycles (cycles are the movement of a wave from one crest to the next crest or one trough to the next trough) per second.A buzzer at 900 times/second = 900 hertzA guitar string at 880 times/2 seconds = 440 hertzA ball that bounces 10 times/50 seconds = 0.2 hertz
21 Light Waves in ActionShorter wavelength colors such as blue and violet hit particles in the sky and reflect back into space.Longer wavelength colors such as red and orange miss more of these particles and therefore are seen by the eye.Laser LightLaser light emits light of only one wavelength.Other light sources emit light of different wavelengths.Light of one wavelength is called coherent.Lasers can be used for:Scanners in storesTo use as a surgical toolMeasure the speed of cars
22 Topic 8 : Beyond LightThe Electromagnetic Spectrum Arrangement of visible light and invisible forms of radiant energy according to wavelength. Decreasing Wavelength Increasing Frequency Visible LightRadio WavesInfraredUltra VioletX RaysGamma Rays
23 1. Infrared RadiationHeat RadiationUses of Infrared RadiationMotion detectorsBurglar alarmsHeat lampsThermographs2. Radio WavesA wave useful for carrying sounds or pictures through the airUses of Radio WavesBroadcasting radio and T.V programsRadarMicrowave ovens for cooking (microwaves are shortest wavelength and highest frequency of radio waves)
25 3. Ultraviolet Radiation Energetic form of radiation that causes tanningDepletion of the Ozone layerOzone in the atmosphere protects us from Ultraviolet radiationUV radiation causes tanningToo much UV radiation can cause cancer4. X RaysRadiation that can penetrate skin and muscleUses of X RaysUsed in hospitals and dentist offices
26 5. Gamma RaysGamma rays result from nuclear reactions and can kill cellsUse of Gamma RaysUsed to treat cancer cells with radiation therapy
27 YOU ARE NOW GOING TO DO: TOPIC 3,4,6,7,8 REVIEW YOU CAN DO THIS WITH A PARTNER!!