Light%20and%20Sound

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Light and Sound

• In this unit
• Properties of light
• Reflection
• Colours
• Refraction
• Properties of sound
• Hearing

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Part 1 Properties of Light

• Light travels in straight lines

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• Light travels VERY FAST around 300,000,000
  meters 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
non-luminous
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• Shadows

Shadows are places where light is blocked
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Properties of Light summary

1. Light travels in straight lines
2. Light travels much faster than sound
3. We see things because they reflect light into our
   eyes
4. Shadows are formed when light is blocked by an
   object

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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 !!!
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Regular 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
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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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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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Using filters

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

Red filter absorbs all colors except red that go
through.
Absorbed light is changed into heat
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Refraction
Refraction is when waves ____ __ or slow down due
to travelling in a different mediums. A medium is
something that waves will travel through. When a
pen is placed in water it looks like this In
this case objects will look not in the correct
position under water
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Other sound effects

• Like light, sound can be reflected.
• Reflected sound reflections are called Echo