# Light and Sound In this unit: Properties of light Reflection Colours

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Light and Sound In this unit: 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:
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.

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

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

When Light Strikes an Object
Light travels in a straight line. It will continue moving in a straight line, until it hit something. Depending on what it hits, light may behave in very different ways.

Reflection When light bounces off a surface, it is called reflection.
When light is reflected it travels in a straight line away from the reflecting surface. Example of Reflection:

Part 2 - Reflection Reflection from a mirror: Mirror Normal
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 ____ _____ 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

Absorption Any time light hits a surface, some of it is absorbed, or taken in. When light is absorbed into a surface it is transformed from light energy, into heat energy. That is why on a sunny day it is cooler to wear a white t-shirt, than a black t-shirt; dark surfaces absorb more light than lighter surfaces.

Refraction Some materials transmit light, or allow light to pass through them. These transparent materials cause light to bend as it is passing through the surface. When the light bends, it makes things look like they do not match up.

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

Let there be light!!! The normal human retina contains two kinds of light sensitive cells: the rod cells (active only in low light) and the cone cells (active in daylight to see colour). Three cones "red" cones (60% of spectrum) "green" cones (30% of spectrum) "blue" cones (10%) of spectrum Colour blindness comes from a reduction complete loss of function of one or more of the different cones.

Different Types of Color Blindness
Monochromacy: occurs when two or all three of the cone pigments are missing and color and lightness vision is reduced to one dimension. Total color blindness Dichromacy: occurs when only one of the cone pigments is missing and color is reduced to two dimensions. - 90% of people affected are male Partial color blindness red-green blue-yellow

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 blue and green makes cyan (light blue) Adding red and green makes yellow Adding all three makes white again

Only red light is reflected
Seeing colour The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: Homework 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 A white hat would reflect all seven colours: White light

Red Green Blue Called this because if you add them, they will produce WHITE light

Using coloured light If we look at a coloured object in coloured light we see something different. For example, : Shirt looks red White light Shorts look blue

In different colours of light it would look different:
Red light Shirt looks red Shorts look black Shirt looks black Blue light Shorts look blue

Using filters Red Filter
Filters can be used to “block” out different colours of light: Red Filter Magenta Filter

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