Presentation on theme: "Light In this unit: Properties of light Types of light Reflection"— Presentation transcript:
1Light In this unit: Properties of light Types of light Reflection ColoursRefraction
2Light In the simplest terms what is light? light is the form of Energy that we can see.light is part of the electromagnetic spectrum of energy
3Types of Light Natural Light Sun Candles or Oil Lamps Wood (fire) Bioluminescence (light produced by living organisms) Firefly, Angular Fish
4Types of Light Artificial Light Incandescent bulbs Florescent bulbs Phosphorescence stored and released later. Ex. paintChemiluminescenceA chemical reaction, Ex. glow sticks
5Cost of LightIf we use light or sources of light then we must also be prepared to pay for the source of the light!How would the cost of light be calculated?What energy source is used to produce most artificial light?So the cost of light is the cost of the electrical energy used to produce it.
6Cost of LightElectrical energy costs money to produce. A watt is a unit of electrical power. The cost is calculated by how much of the electrical energy is used over a certain period of time. Calculations are made in kW.h's. 1 kW.h is 1000 watts of electrical energy operating for 1 hour.
7Convert 60W to kW by dividing by 1000 Calculate the number of kW hours Example: Calculate the cost of leaving a 60W light bulb on for 10 hours.Convert 60W to kW by dividing by 1000Calculate the number of kW hoursTo complete the calculation we need to know how much is charged per hour.60 W / 1000 = 0.06 kW0.06 kW x 10 hours = 0.6 kW.h
8Cost of Light $0.48/10 hour period Calculate the cost by multiplying the number of hours by the cost per kW.hIf the cost per kW.h is $0.08(4.8 cents - or about 5 cents)Now multiply this by10 hoursThe cost of electricity to operate the 60W light bulb for 1 hour would be time x Cost 0.6 kW.h x $0.08 = $0.048$0.048 x 10 hours=$0.48/10 hour period
9Cost of ElectricityComplete questions #’s 1a, 1b, 1c, and #2 from the BLM sheet 3-3Answers:1(a) Cost = 0.1 kW x 9 h x 8¢/kW•h = 7.2¢1(b) Cost = 1.5 kW x 3 h x 8¢/kW•h = 36¢1(c) Cost = 0.5 kW x 7 h x 8¢/kW•h = 28¢2. There are about 226 days between October 8 and May 22. Cost = 1 kW x 226 days x 12 h/day x 8¢/kW•h = $216.96
10Part 1 – Properties of Light Light travels in straight lines:Laser
11Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.
12Light travels much faster than sound. For example: 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.
13We see things because they reflect light into our eyes: Homework
14Luminous and non-luminous objects A luminous object is one that produces light.A non-luminous object is one that reflects light.Luminous objectsReflectors
15ShadowsShadows are places where light is “blocked”:Rays of light
16Properties of Light summary Light travels in straight linesLight travels much faster than soundWe see things because they reflect light into our eyesShadows are formed when light is blocked by an object
17Part 2 - Reflection Reflection from a mirror: Mirror Normal Incident rayReflected rayAngle of incidenceAngle of reflectionMirror
18Angle of incidence = Angle of reflection The Law of ReflectionAngle of incidence = Angle of reflectionIn other words, light gets reflected from a surface at ____ _____ angle it hits it.The same !!!
19Clear 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
20Using mirrorsTwo examples:2) A car headlight1) A periscope
21ColourWhite 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.
22The colours of the rainbow: RedOrangeYellowGreenBlueIndigoVioletROY G BIV
23Adding coloursWhite 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 blue and green makes cyan (light blue)Adding red and green makes yellowAdding all three makes white again
24Only red light is reflected Seeing colourThe colour an object appears depends on the colours of light it reflects.For example, a red book only reflects red light:HomeworkWhitelightOnly red light is reflected
25A white hat would reflect all seven colours: A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):Purple lightA white hat would reflect all seven colours:Whitelight
26Using coloured lightIf we look at a coloured object in coloured light we see something different. For example, consider a football kit:Shirt looks redWhitelightShorts look blue
27In different colours of light this kit would look different: RedlightShirt looks redShorts look blackShirt looks blackBluelightShorts look blue
28Some further examples: ObjectColour of lightColour object seems to beRed socksRedBlueBlackGreenBlue teddyGreen camelMagenta bookHomework
29Using filters Red Filter Filters can be used to “block” out different colours of light:Red FilterMagenta Filter
30Investigating filters Colour of filterColours that could be “seen”RedGreenBlueCyanMagentaYellow
33Words – speed up, water, air, bent, medium RefractionRefraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this:In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______.Words – speed up, water, air, bent, medium