# Light and Sound In this unit: 1)Properties of light 2)Reflection 3)Refraction 4)Colours.

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Light and Sound In this unit: 1)Properties of light 2)Reflection 3)Refraction 4)Colours

What is Light? A form of ENERGY! Scientific Definition: A stream of photons that are massless particles each travelling with wavelike properties at the speed of light. A photon is the smallest quantity of energy which can be transported.

Where does light come from? The sun gives off light due to nuclear fission Other methods will be discussed later…. The methods of energy transfer: 1.Conduction  requires contact 2.Convection  requires a medium (like air) 3.Radiation  a method of energy transfer that does not need a medium and travels at the speed of light

Properties of Light Light travels in straight lines: Light does not need a medium to travel Laser

Light Travels as a wave What is wavelength? What is Amplitude? What is frequency?

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.

Electromagnetic Spectrum What is white light? How do we see colours? It turns out that visible light is just a small part of a spectrum called Electromagnetic Radiation

The Wave Model of Light 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.

Newton was the first to note that white light breaks into the colours of a rainbow when it passes through a prism. These colours are called a Spectrum.

When light from the Sun (White Light) is broken down, it’s Spectrum looks like this. White Light is made up of shades of Red, Orange, Yellow, Green, Blue, and Violet. Roy G BV. A mnemonic for remembering the order of rainbow colours is the name Roy G BV.

Newton noted that the individual coloured lines could not be separated further. These lines are pure colours and are identified by a frequency and wavelength number. Light is produced when electrons change energy levels. The Conceptual definition of light is; Light is produced when electrons change energy levels.

Our ears cannot hear some high sound frequencies that dogs can. Similarly, our eyes cannot “see” some of the colours of light.

For instance, you cannot see if an iron is hot or not. Our eyes are not sensitive to the “colour” the iron emits but our hands can feel it. The “colour” hot irons emit is called Infra Red Radiation. Some snakes can see Infra Red Radiation.

The Visible Light Spectrum is a very small part of a much larger spectrum called the Electromagnetic Spectrum.

How do we see? We do not see light that does not enter our eyes.

How do we see? We don’t see light directed away from our eyes unless it is reflected into our Eye-Brain by something.

How do we see things? We see things because they reflect light into our eyes: Homework

Can you see the Eye-Brain’s feet?

Since no ray of light can go straight from the Eye-Brain’s feet into your eyes, you can’t see them. Experience has trained our Eye-Brain to expect that things are located in the direction that the light comes from.

Luminous and non-luminous objects A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminous objectsReflectors

Atoms in Luminous Objects emit light rays in all directions produced from other energy sources.

Rays of light travel from the object to the observer’s eye through a Medium. A Transparent Medium allows nearly all the rays to pass straight through unaltered. Air is a transparent medium.

An Opaque Medium absorbs or scatters all the rays. A text book is an opaque medium.

A Translucent Medium transmits and scatters the rays. The medium indicates whether it is being illuminated but the object cannot be clearly seen. Wax paper is a translucent medium.

Light and Matter Transparent Transmit light freely - absorb and reflect very little light. Eg. Clear glass, clear plastic, windowTranslucent Transmit some light but not enough to see clearly Eg. Frosted window/glassOpague Objects that absorb and reflect light but do not transmit it

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: Incident ray Normal 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: 1) A periscope 2) A car headlight

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 all three makes white again Adding red and green makes yellow

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

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 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: White light Shorts look blue Shirt looks red

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

Some further examples: ObjectColour of light Colour object seems to be Red socks Red BlueBlack GreenBlack Blue teddy RedBlack Blue Green Green camel Red Blue Green Magenta book Red Blue Green

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

Investigating filters Colour of filterColours that could be “seen” Red Green Blue Cyan Magenta Yellow

Red Magenta White Yellow BlueGreen Cyan

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

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