KS3 Light

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KS3 Light
Miss Scale Greenhill School
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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
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• Shadows

Shadows are places where light is blocked
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Properties of Light summary

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

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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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Clear 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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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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Red
Magenta
Yellow
White
Blue
Green
Cyan
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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
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Using filters

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

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Investigating filters
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Red
White
Blue
Green
Magenta
Yellow
Cyan
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Refraction

• Refraction is Bending Light
• When light travels from one substance to
  another, the speed it travels changes
• The change in speed means it can BEND

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Refraction through a glass block
Wave slows down but is not bent, due to entering
along the normal
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Refraction
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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The Eye
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The Parts of the Eye

• IRIS Coloured part, controls size of pupil
• PUPIL Opening that controls the amount of light
  into the eye
• CORNEA Transparent layer over the eye
• LENS Focuses light coming into the eye
• RETINA Area at the back of the eye where the
  image is projected
• OPTIC NERVE Sends the signal to the brain