Light Waves Notes. Part 1 – Properties of Light Light travels in straight lines: Laser.

Light Waves Light Waves NotesNotes

Part 1 – Properties of Part 1 – Properties of LightLight

Light travels in straight lines:

Laser

Light travels VERY FAST – around 300,000 kilometres per second.

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

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.

We see things because they reflect light into our eyes:

Homework

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

Part 2 - ReflectionPart 2 - ReflectionReflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

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

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

Using mirrorsUsing mirrorsTwo examples:

1) A periscope

2) A car headlight

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.

The colours of the rainbow:The colours of the rainbow:

RedOrangeYellowGreenBlue

IndigoViolet

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

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

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

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

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

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

Light & Colour Bill NyeLight & Colour Bill Nye

• http://www.youtube.com/watch?v=gtgBHsSzCPE

Using filtersUsing filtersFilters can be used to “block” out different colours of

light:

Red Filte

r

Magenta

Filter

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

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

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

Due to change in mediummedium, the phase velocity of the wave is changed but its frequency remains constant (the same).

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

Drawing sounds…Drawing sounds…

This sound wave has a _____ frequency:

This sound wave has a ___ _frequency:

high

High pitch

low

Low pitch

Drawing sounds…Drawing sounds…

This sound wave has a _____ amplitude:

This sound wave has a _____ amplitude:

high

Loud

low

Quiet

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