Light In this unit:3) Properties of light4) Reflection5) Colours6) Refraction
Part 1 – Properties of Light Light travels in straight lines: Las e r
Light travels VERY FAST – around 300,000 kilometres per second.At this speed it cango around the world 8times in one second.
Light travels much faster than sound. For example: 2) 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
ShadowsShadows are places where light is “blocked”: Rays of light
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
Part 2 - Reflection Reflection from a mirror: NormalIncident ray Reflected ray Angle of Angle of incidence reflection Mirror
The Law of Reflection Angle of incidence = Angle of reflectionIn other words, light gets reflected from a surface at____ _____ angle it hits it. The same !!!
Clear vs. Diffuse ReflectionSmooth, shiny surfaces have a clear reflection:Rough, dull surfaces havea diffuse reflection.Diffuse reflection is whenlight is scattered indifferent directions
Using mirrorsTwo examples: 2) A car headlight 1) A periscope
ColourWhite light is not a single colour; it is made up of a mixture of the seven colours of the rainbow.We can demonstrate this bysplitting white light with aprism:This is how rainbows areformed: sunlight is “split up”by raindrops.
The colours of the rainbow: Red Orange Yellow Green Blue Indigo Violet
RefractionRefraction is when waves ____ __ or slow down due totravelling in a different _________. A medium issomething that waves will travel through. When a pen isplaced in water it looks like this:In this case the light rays are slowed down by the waterand are _____, causing the pen to look odd. The twomediums in this example are ______ and _______. Words – speed up, water, air, bent
Adding colours White light can be split up to make separate colours. These colours can be added together again.Adding blue and red Adding blue andmakes magenta green makes cyan(purple) (light blue)Adding red Adding alland green three makesmakes yellow white again
Seeing colourThe colour an object appears depends on the colours of light it reflects.For example, a red book only reflects red light: White Only red light light is reflected
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
Using coloured lightIf 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 Shirt looks red light Shorts look black Shirt looks black Blue light Shorts look blue
Some further examples: Colour object Object Colour of light seems to be Red Red Red socks Blue Black Green Black Red Black Blue teddy Blue Green RedGreen camel Blue Green RedMagenta book Blue Green