light waves notes. part 1 – properties of light light travels in straight lines: laser
TRANSCRIPT
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Light Waves Light Waves NotesNotes
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Part 1 – Properties of Part 1 – Properties of LightLight
Light travels in straight lines:
Laser
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Light travels VERY FAST – around 300,000 kilometres per second.
At this speed it can go around the world 8 times in one second.
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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.
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We see things because they reflect light into our eyes:
Homework
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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
SunStarsLight Bulb (when on)Firefly
MirrorMoonPersonDeskPaper
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Part 2 - ReflectionPart 2 - ReflectionReflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of incidence
Angle of reflection
Mirror
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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 !
!!
the same
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Clear vs. Diffuse ReflectionClear vs. Diffuse Reflection
Smooth, shiny surfaces have a _____ reflection:
Rough, dull surfaces have a ______ reflection.
Diffuse reflection is when light is scattered in different directions
Clear
Diffuse
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Using mirrorsUsing mirrorsTwo examples:
1) A periscope
2) A car headlight
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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.
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The colours of the rainbow:The colours of the rainbow:
RedOrangeYellowGreenBlue
IndigoViolet
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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
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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
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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
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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
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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
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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
blue
black
blackblackgreenred
blue
black
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Light & Colour Bill NyeLight & Colour Bill Nye
• http://www.youtube.com/watch?v=gtgBHsSzCPE
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Using filtersUsing filtersFilters can be used to “block” out different colours of
light:
Red Filte
r
Magenta
Filter
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Investigating filtersInvestigating filters
Colour of filter Colours that could be “seen”
Red
Green
Blue
Cyan
Magenta
Yellow
redgreen
blue
Blue, green, cyanRed, blue, magenta
Red, green, yellow
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Red
Magenta
White
Yellow
Blue Green
Cyan
(No Color)
Primary Colours of Primary Colours of LightLight
Black
(All colors)
Secondary Colours of Secondary Colours of LightLight
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RefractionRefraction
Refraction is when waves _______ or slow down due to travelling in a different _________. A medium is the area or space that waves will travel through.
For example, if you put a pen in a cup of water, the light rays are slowed down by the water and are _____, causing the pen to look odd.
~Two examples on next slide~
mediumSpeed up
bent
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Due to change in mediummedium, the phase velocity of the wave is changed but its frequency remains constant (the same).
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Sound – The basicsSound – The basics
We hear things when they ________.
If something vibrates with a ____________
(vibrates very ______) we say it has a _____ pitch.
If something vibrates with a ___________ (vibrates ______) we say it has a ____ pitch.
vibrate
High frequency
fast
Low frequency
slow low
high
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Drawing sounds…Drawing sounds…
This sound wave has a _____ frequency:
This sound wave has a ___ _frequency:
high
High pitch
low
Low pitch
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Drawing sounds…Drawing sounds…
This sound wave has a _____ amplitude:
This sound wave has a _____ amplitude:
high
Loud
low
Quiet
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Conclusion:
The pitch or note of a sound that we hear is determined by its wavelength or its frequency.
•The shorter the wavelength, the higher the frequency becomes, and the higher the pitch that we hear.
•The amplitude of a sound wave is the same thing as loudness.
• The wavelength of a wave is independent of its amplitude [loudness] and inversely proportional to its frequency.
Independent— wavelength does not affect loudness.
Inversely proportional—high frequency = short wavelength, low frequency = long wavelength