1.light pptdl

8/3/2019 1.LIGHT Pptdl

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Properties of Light

Light travels in straight lines:

Laser


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Light travels VERY FAST around

300,000 kilometres per second.

At this speed it cango around the world 8times in one second.


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Light travels much faster than sound. For example:

1) Thunder and lightningstart at the same time,but we will see the

lightning first.

2) When a starting pistol

is fired we see thesmoke first and thenhear 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:

Rays of light


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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 lightinto our eyes

4) Shadows are formed when light is blocked

by an object


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ReflectionReflection from a mirror:

Incident ray

Normal

Reflected ray

Angle ofincidence

Angle ofreflection

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.

Thesame !!!


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Clear vs. Diffuse Reflection

Smooth, shiny surfaceshave a clearreflection:

Rough, dull surfaces havea diffuse reflection.

Diffuse reflectionis whenlight is scattered indifferent directions


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Using mirrors

Two examples:

1) A periscope

2) A car headlight


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Colour

White light is not a single colour; it is madeup of a mixture of the seven colours of therainbow.

We can demonstrate this bysplitting white light with aprism:

This is how rainbows areformed: sunlight is split upby raindrops.


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The colours of the rainbow:

Red

OrangeYellow

Green

Blue

Indigo

Violet


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Adding 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 redmakes magenta(purple)

Adding blue andgreen makes cyan

(light blue)

Adding allthree makeswhite again

Adding redand greenmakes yellow


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Seeing colour

The colour an object appears depends on the coloursof light it reflects.

For example, a red book only reflects red light:

White

light Only red lightis 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 light

If we look at a coloured object in colouredlight we see something different. Forexample, consider a football kit:

Whitelight

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 objectseems to be

Red socksRed RedBlue Black

Green Black

Blue teddy

Red Black

Blue

Green

Green camel

Red

BlueGreen

Magenta book

Red

Blue

Green


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Using filtersFilters can be used to block out different colours of light:

RedFilter

MagentaFilter


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Investigating filters

Colour of filter Colours that could be seen

Red

GreenBlue

Cyan

Magenta

Yellow


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Red

Magenta

White

Yellow

Blue Green

Cyan


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Refraction

Refraction is when waves speed up or slow down due totravelling in a different MEDIA. A medium is somethingthat waves will travel through. When a pen is placed inwater it looks like this:

In this case the light rays are slowed down by the waterand are bent, causing the pen to look odd. The twomediums in this example are waterand air.


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