19/02/2019 KS3 Light W Richards Worthing High School

Light travels in straight lines: 19/02/2019 Properties of Light Light travels in straight lines: Laser

Light travels VERY FAST – around 300,000 kilometres per second. 19/02/2019 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: 19/02/2019 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 they reflect light into our eyes: 19/02/2019 We see things because they reflect light into our eyes: Homework

Luminous and non-luminous objects 19/02/2019 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 19/02/2019 Shadows Shadows are places where light is “blocked”: Rays of light

Properties of Light summary 19/02/2019 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

Reflection Reflection from a mirror: Mirror Normal Angle of incidence 19/02/2019 Reflection from a mirror: Normal Incident ray Reflected ray Angle of incidence Angle of reflection Mirror

Angle of incidence = Angle of reflection 19/02/2019 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 19/02/2019 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 19/02/2019 Using mirrors Two examples: 2) A car headlight 1) A periscope

Colour 19/02/2019 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: 19/02/2019 Red Orange Yellow Green Blue Indigo Violet

19/02/2019 Red Magenta Yellow White Blue Green Cyan

19/02/2019 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 19/02/2019 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: 19/02/2019 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

19/02/2019 Using coloured light If 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: 19/02/2019 In different colours 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: 19/02/2019 Object Colour of light Colour object seems to be Red socks Red Blue Black Green Blue teddy Green camel Magenta book Homework

Using filters Red Filter 19/02/2019 Using filters Filters can be used to “block” out different colours of light: Red Filter Magenta Filter

Investigating filters 19/02/2019 Investigating filters Colour of filter Colours that could be “seen” Red Green Blue Cyan Magenta Yellow

Red Blue Green White Yellow Cyan Magenta 19/02/2019 Red Blue Green White Yellow Cyan Magenta

Refraction through a glass block: 19/02/2019 Wave slows down and bends towards the normal due to entering a more dense medium Wave slows down but is not bent, due to entering along the normal Wave speeds up and bends away from the normal due to entering a less dense medium

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Words – speed up, water, air, bent, medium 19/02/2019 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, medium