light in this unit: 1)properties of light 2)types of light 3)reflection 4)colours 5)refraction...
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LightLight
In this unit:
1) Properties of light2) Types of light3) Reflection4) Colours5) Refraction6) Reflection
LightLight
• 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
Types of Light
• Natural Light• Sun • Candles or Oil
Lamps • Wood (fire) • Bioluminescence
(light produced by living organisms) Firefly, Angular Fish
Types of Light
• Artificial Light• Incandescent bulbs• Florescent bulbs• Phosphorescence
stored and released later. Ex. paint
• Chemiluminescence• A chemical reaction,
Ex. glow sticks
Cost of LightCost of Light
If 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.
Cost of Light
• Electrical 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.
Example: Calculate the cost of leaving a 60W light bulb
on for 10 hours. 1. Convert 60W to kW
by dividing by 1000
2. Calculate the number of kW hours
3. To complete the calculation we need to know how much is charged per hour.
• 60 W / 1000 = 0.06 kW
• 0.06 kW x 10 hours = 0.6 kW.h
Cost of Light
• Calculate the cost by multiplying the number of hours by the cost per kW.h
• If the cost per kW.h is $0.08
• (4.8 cents - or about 5 cents)
• Now multiply this by10 hours
• The cost of electricity to operate the 60W light bulb for 1 hour would be time x Cost0.6 kW.h x $0.08 = $0.048
• $0.048 x 10 hours=
• $0.48/10 hour period
Cost of ElectricityCost of Electricity
Complete questions #’s 1a, 1b, 1c, and #2 Complete questions #’s 1a, 1b, 1c, and #2 from the BLM sheet 3-3from the BLM sheet 3-3
Answers:Answers: 1(a) Cost = 0.1 kW x 9 h x 8¢/kW•h = 1(a) Cost = 0.1 kW x 9 h x 8¢/kW•h = 7.2¢7.2¢ 1(b) Cost = 1.5 kW x 3 h x 8¢/kW•h = 1(b) Cost = 1.5 kW x 3 h x 8¢/kW•h = 36¢36¢ 1(c) Cost = 0.5 kW x 7 h x 8¢/kW•h = 1(c) Cost = 0.5 kW x 7 h x 8¢/kW•h = 28¢28¢ 2. There are about 226 days between 2. There are about 226 days between
October 8 and May 22. Cost = 1 kW x 226 October 8 and May 22. Cost = 1 kW x 226 days x 12 h/day x 8¢/kW•h = days x 12 h/day x 8¢/kW•h = $216.96$216.96
Part 1 – Properties of Part 1 – Properties of LightLight
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.
We see things because they reflect light into our eyes:
Homework
Luminous and non-luminous objects
A luminous object is one that produces light.
A non-luminous object is one that reflects light.
Luminous objects Reflectors
Shadows
Shadows are places where light is “blocked”:
Rays of light
Properties of Light Properties of Light summarysummary
1) Light travels in straight lines2) Light travels much faster than sound3) We see things because they reflect
light into our eyes4) Shadows are formed when light is
blocked by an object
Part 2 - ReflectionPart 2 - ReflectionReflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of incidence
Angle of reflection
Mirror
The Law of ReflectionThe Law of Reflection
Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection
In other words, light gets reflected from a surface at ____ _____ angle it hits it.
The same !
!!
Clear vs. Diffuse ReflectionClear 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 mirrorsUsing mirrorsTwo examples:
1) A periscope
2) A car headlight
ColourColour
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:The colours of the rainbow:
RedOrangeYellowGreenBlue
IndigoVioletRROOYY GG BBIIVV
Adding coloursAdding 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 all three makes white again
Adding red and green makes yellow
Seeing colourSeeing colourThe 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 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 light
White
light
Using coloured lightUsing coloured light
If we look at a coloured object in coloured light we see something different. For example, consider a football kit:
White
light
Shorts look blue
Shirt looks red
In different colours of light this kit would look different:
Red
lightShirt looks red
Shorts look black
Blue
light
Shirt looks black
Shorts look blue
Some further examples:
Object Colour of lightColour object seems to be
Red socks
Red Red
Blue Black
Green Black
Blue teddy
Red Black
Blue
Green
Green camel
Red
Blue
Green
Magenta book
Red
Blue
Green
Using filtersUsing filtersFilters can be used to “block” out different colours of
light:
Red Filte
r
Magenta
Filter
Investigating filtersInvestigating filters
Colour of filter Colours that could be “seen”
Red
Green
Blue
Cyan
Magenta
Yellow
ColorColor MixesMixes WellWell
http://www.explorelearning.com/index.cfm?method=cResource.dspResourcesForCourse&CourseID=332
Red
Magenta
White
Yellow
Blue Green
Cyan
RefractionRefraction
Refraction 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
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