Light Waves Notes

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Light Waves Notes
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Part 1 Properties of Light

• Light travels in straight lines

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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

• 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
Sun Stars Light Bulb (when on) Firefly
Mirror Moon Person Desk Paper
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Part 2 - Reflection

• Reflection from a mirror

Normal
Reflected ray
Incident ray
Angle of reflection
Angle of incidence
Mirror
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• 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
The same !!!
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Clear vs. Diffuse Reflection

• Smooth, shiny surfaces have a _____ reflection

Clear
Rough, dull surfaces have a ______
reflection. Diffuse reflection is when light is
scattered in different directions
Diffuse
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Using mirrors

• Two examples

2) A car headlight
1) A periscope
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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.
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The colours of the rainbow

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

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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 blue and green makes cyan (light blue)
Adding all three makes white again
Adding red and green makes yellow
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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
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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
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Using coloured light

• If we look at a coloured object in coloured light
  we see something different. For example,
  consider a football kit

Shirt looks red
White light
Shorts look blue
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• In different colours of light this kit would look
  different

Red light
Shirt looks red
Shorts look black
Shirt looks black
Blue light
Shorts look blue
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Some further examples
Object Colour of light Colour object seems to be
Red socks Red Red
Red socks Blue Black
Red socks Green Black
Blue teddy Red Black
Blue teddy Blue
Blue teddy Green
Green camel Red
Green camel Blue
Green camel Green
Magenta book Red
Magenta book Blue
Magenta book Green
blue
black
black
black
green
red
blue
black
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Light Colour Bill Nye

• http//www.youtube.com/watch?vgtgBHsSzCPE

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Using filters

• Filters can be used to block out different
  colours of light

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Investigating filters
Colour of filter Colours that could be seen
Red
Green
Blue
Cyan
Magenta
Yellow
red
green
blue
Blue, green, cyan
Red, blue, magenta
Red, green, yellow
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Red
White
Blue
Green
(All colors)
Primary Colours of Light
Black
Magenta
Yellow
Cyan
(No Color)
Secondary Colours of Light
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Refraction
Speed up
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
medium
bent
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?Due to change in medium, the phase velocity of
the wave is changed but its frequency remains
constant (the same).
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Sound The basics
vibrate
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.
High frequency
fast
high
Low frequency
low
slow
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Drawing sounds
This sound wave has a _____ frequency
high
High pitch
This sound wave has a ___ _frequency
low
Low pitch
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Drawing sounds
This sound wave has a _____ amplitude
high
Loud
This sound wave has a _____ amplitude
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 proportionalhigh frequency
short wavelength, low frequency
long wavelength