Light In this unit: Properties of light Reflection Colors Refraction
Light travels VERY FAST – around 300,000 kilometers per second. (that’s 670,000 mph) At this speed it can go around the world 8 times in one second.
Speed of Light Light is so fast, physicists measure light with ‘light years’. A light year is the distance that light travels in one year. Our nearest spiral galaxy is Andromeda. It is 2.5 million light years away
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.
We see things because the object reflects light into our eyes: Homework
Color White (visible) light is not a single color; it is made up of a mixture of the seven colors 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 colors of the rainbow: Red Orange Yellow Green Blue Indigo Violet ROY G BIV
Only red light is reflected Seeing Color An object looks a certain color because it reflects that color light to our eyes and absorbs all other colors. For example, a red book only reflects red light: Homework White light Only red light is reflected
The Color White An object appears white because it reflects all colors from white light: White light White light
The Color Black Black can be thought of as a lack of color. A black object absorbs all white light and reflects no color at all
Shadows are places where light is “blocked”: Rays of light
There are two types of objects when dealing with light A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminous objects Reflectors
Reflection Reflection from a mirror: Mirror Normal Angle of incidence Incident ray Reflected ray Angle of incidence Angle of reflection Mirror
Angle of incidence = Angle of reflection The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at the same 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
Adding colors White light can be split up to make separate colors. These colours can be added together again. The primary colors of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding red and green makes yellow Adding all three makes white again
A white hat would reflect all seven colors: 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 colors: White light
Using colored light If we look at a colored object in coloured light we see something different. For example, consider a football kit: Shirt looks red White light Shorts look blue
In different colors 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 Color of light Color object seems to be Red socks Red Blue Black Green Blue teddy Green camel Magenta book Homework
Using filters Red Filter Filters can be used to “block” out different colors of light: Red Filter Magenta Filter
Investigating filters Color of filter Colors that could be “seen” Red Green Blue Cyan Magenta Yellow
Words – speed up, water, air, bent 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
Red Blue Green White Yellow Cyan Magenta