Light In this unit:1) Properties of light2) Mirrors3) Colors
1 – Properties of LightLight travels in straight lines:Laser
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: 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
ShadowsShadows are places where light is “blocked”: Rays of light
Properties of Light summary1) Light travels in straight lines2) Light travels much faster than sound3) We see things because they reflect light into our eyes4) Shadows are formed when light is blocked by an object
ReflectionReal Image – – Real image is formed when reflected rays of light actually meet at a point. – Always inverted. – It is formed on the screen.
ReflectionVirtual Image– – “Not Real” because it cannot be projected – Image only seems to be there!
Virtual Images in Plane Mirrors Rays seem to come from behind the mirror, but, of course, they dont. It is virtually as if the rays were coming from behind the mirror. "Virtually": the same as if As far as the eye-brain system is concerned, the effect is the same as would occur if the mirror were absent and the chess piece were actually located at the spot labeled "virtual If light energy doesnt flow from the image". image, the image is "virtual".
Plane Mirror •Useful to think in terms of images“real” you “image” you
Convex Lenses Thicker in the centerthan edges. – Lens that converges (brings together) light The Magnifier rays. – Forms real images and virtual images depending on position of the object
Concave LensesLenses that arethicker at the edgesand thinner in thecenter. – Diverges light The De-Magnifier rays – All images are erect and reduced.
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
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 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