Presentation on theme: "Shadows Shadows are places where light is “blocked”: Rays of light."— Presentation transcript:
1 ShadowsShadows are places where light is “blocked”:Rays of light
2 Luminous and non-luminous objects A luminous object is one that produces light.A non-luminous object is one that reflects light.Luminous objectsReflectors
3 We see things because they reflect light into our eyes: Homework
4 Reflection Reflection from a mirror: Mirror Normal Angle of incidence Incident rayReflected rayAngle of incidenceAngle of reflectionMirror
5 Angle of incidence = Angle of reflection The Law of ReflectionAngle of incidence = Angle of reflectionIn other words, light gets reflected from a surface at ____ _____ angle it hits it.The same !!!
6 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
7 Using mirrorsTwo examples:2) A car headlight1) A periscope
8 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 by splitting white light with a prism:This is how rainbows are formed: sunlight is “split up” by raindrops.
9 Only red light is reflected Seeing colourThe colour an object appears depends on the colours of light it reflects.For example, a red book only reflects red light:HomeworkWhitelightOnly red light is reflected
10 A white hat would reflect all seven colours: Seeing Colour: A pair of purple trousers would reflect purple light ( i.e. red and blue light, as purple is made up of red and blue):Purple lightA white hat would reflect all seven colours:Whitelight
11 Refraction through a glass block: Wave slows down and bends towards the normal due to entering a more dense mediumWave slows down but is not bent, due to entering along the normalWave speeds up and bends away from the normal due to entering a less dense medium
12 Words – speed up, water, air, bent, medium RefractionRefraction 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
13 Examples of Refraction Is the fish deeper or shallower than its image appears to be?Should you stab above or below the image of the fish to spear it?
14 Examples of Refraction Explain why:You can’t see the coin in the cup without waterYou can see the coin in the cup with water
15 Speed of soundThe speed of sound in air is around 330 m/s. What happens when sound travels through different materials?Speed of sound(in m/s)MaterialConclusion – the denser the material, the faster sound travels through it
16 Making Sounds A sound is made when an object or material VIBRATES. Take, for example, a guitar.To make a sound with a guitar a string has to vibrate. We can raise the pitch of the sound a guitar makes by doing three things:1) _________ the length of the string2) _________ the string3) Using a _________ stringWe can make the sound louder by ________ the string harderWords – tightening, thinner, increasing, plucking
17 Using an oscilloscope 1) Quiet sound, low frequency: 2) Quiet sound, high frequency:3) Loud sound, low frequency:4) Loud sound, high frequency:
18 How sound travels…As we know, sound waves are formed when something vibrates. But how does the sound reach our ears?Air molecules2) The vibrations pass through air by making air molecules vibrate3) These vibrations are picked up by the ear1) An object makes a sound by vibrating
19 How does the ear work?1) Sound waves are “funnelled” into the ear by the pinna5) The electrical signals are then sent to the brain3) These vibrations make the ear bones vibrate4) These vibrations are turned into electrical signals in the cochlea2) These vibrations make the ear drum vibrate
20 The EyeRead the definitions on the next slide, then label the eye anatomy diagram below.
21 The Eye DefinitionsCornea - the clear, dome-shaped tissue covering the front of the eye.Iris - the colored part of the eye - it controls the amount of light that enters the eye by changing the size of the pupilLens - a crystalline structure located just behind the iris - it focuses light onto the retinaOptic nerve - the nerve that transmits electrical impulses from the retina to the brainPupil - the opening in the center of the iris- it changes size as the amount of light changes (the more light, the smaller the hole)Retina - sensory tissue that lines the back of the eye. It contains millions of photoreceptors (rods and cones) that convert light rays into electrical impulses that are relayed to the brain via the optic nerveVitreous - a thick, transparent liquid that fills the center of the eye - it is mostly water and gives the eye its form and shape (also called the vitreous humor)
22 Light WavesLight energy travels in the form of a transverse wave. Below is a picture of a light wave
23 Sound Waves Sound energy travels in the form of a longitudinal wave Sound Waves Sound energy travels in the form of a longitudinal wave. Below is a picture of a longitudinal wave travelling along a spring.
24 Sound WavesWhen a longitudinal wave moves through a material, the particles of the material move backwards and forwards along the direction in which the wave is travelling.