Light and Sound
In this unit:
1) 2) 3) 4) 5) 6)
Properties of light Reflection Colours Refraction Properties of sound Hearing
Part 1 – Properties of Light
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
Shadows
Shadows are places where light is “blocked”:
Rays of light
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
Part 2 - Reflection
Reflection from a mirror:
Normal
Incident ray Reflected ray
Angle of incidence
Angle of reflection
Mirror
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 !!!
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
Using mirrors
Two examples:
2) A car headlight
1) A periscope
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.
The colours of the rainbow:
Red Orange Yellow Green Blue Indigo Violet
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 red and green makes yellow
Adding blue and green makes cyan (light blue) Adding all three makes white again
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
(and red and blue, as purple is made up of red and blue):
A pair of purple trousers would reflect purple light
Purple light
A white hat would reflect all seven colours:
White
light
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
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
Some further examples:
Object Red socks Colour of light
Red Colour object seems to be Red
Blue Green Red
Black Black Black
Blue teddy
Blue Green
Red
Green camel
Blue Green Red
Magenta book
Blue Green
Using filters
Filters can be used to “block” out different colours of light:
Red Filter
Magenta Filter
Investigating filters
Colour of filter
Red Green Blue
Cyan Magenta
Colours that could be “seen”
Yellow
Red
Blue
Green
White
Yellow
Cyan
Magenta
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
Sound – The basics
We hear things when they vibrate.
If something vibrates with a high frequency (vibrates very ______) we say it has a _____ pitch. If something vibrates with a low frequency (vibrates ______) we say it has a ____ pitch. The lowest frequency I could hear was…
Words – slowly, low, high, quickly
Drawing sounds…
This sound wave has a _____ frequency:
This sound wave has a ___ _frequency:
Drawing sounds…
This sound wave has a _____ amplitude (loud):
This sound wave has a _____ amplitude (quiet):
Hearing problems
Our hearing range can be damaged by several things: 1) Too much ear wax! 2) Damage to the auditory nerve
3) Illness or infections
4) Old age (not like Mr Richards)
Other sound effects…
Like light, sound can be… 1) Reflected – sound reflections are called ______.
2) Refracted – this is why you might sound strange if you try talking underwater
The Ear
Label your diagram with the following:
These bones are vibrated by the eardrum This tube carries the sound towards the eardrum This part is used to help us keep our balance This part “picks up” the vibrations This part of the ear contains many small hairs with turn vibrations into an electrical signal
This part connects the ear to the mouth This part “channels” the sound towards the ear drum
The Ear