SOUND

1. LIGHT & SOUND

2. & Light Sound We study light and sound together because they are both forms of energy and they have some physical properties in common. But what exactly are those properties? Let’s have a look….

3. & Light Sound Waves • Both light and sound travel to us as waves. The waves transmit the energy to make the light we can see and the sound we can hear. • When we modify the kinds of waves that make light, we see different colours. • When we modify sound waves we make different kinds of sounds such as louder or softer sounds or ones with a higher or lower pitch. What do the light and sound waves look like? Are they the same as waves that are formed in the water?

4. Waves Amplitude Wave Length

5. Wave Length Waves

6. & Light Sound Waves Peak Amplitude Trough Wave length Wave length What else can I learn about waves?

7. & Light Sound Waves • Even though the types of waves are different, they have some properties that are similar. • Some of those properties are how the waves travel and how they react when they hit a surface. • Let’s have a look at those properties now...

8. & Light Sound Consider this straight line, it could represent a mirror or a wall….. • Now what happens if we shine a light, roll a ball, send a water wave or a sound wave into it……... where will the light or the ball go or the sound go? I see. But does the angle of incidence always equal the angle of reflection? Normal Angle of incidence Angle of reflection But what do I call all this? Plane

9. & Light Sound MMmmm it appears that the incidence ray and the reflected ray always travel in straight lines and the angle of incidence always equals the angle of reflection. Normal Cool. That must be the law of reflection. Incidence rays Reflected rays

10. & Light Sound According to my calculation the law of reflection should also exist if the surface of reflection is curved instead of plane. Let’s see…. Focal point Yes, but what is it all called? Concave surface Focal length

11. Light MMMmmm that reminds me of how a lens works…..like the ones in my groovy glasses. Not exactly my friend. My calculations show that light bends when it travels through lenses like the ones in your groovy glasses. Cool! That must be the law of refraction (not to be confused with the law of reflection).

12. Light Normal MMmmm so the angle of refraction appears to be smaller than the angle of incidence because it bends towards the normal. But how does that relate to my groovy glasses?? Angle of incidence Air Water or glass Angle of refraction

13. Light Well my calculations state that converging lenses refract the light together (like in the top lens) and diverging lenses refract the light outwards. And what do you call those two different types of lenses? Converging/convex Diverging/concave

14. Light Hi! I’m Mr. BIV and I want to know when are we going to do the prism trick? In a minute ROY, let me just tell you about my last set of calculations…it is amazing. Did you know that light travels at about 300 million meters per second? Through glass it travels at about 1.9 million meters per second so it really does slow down quite a bit.

15. Light Listen Pete, all this talk about light has made me wonder? What actually is it and where does it come from? Don’t know man, I’ll call Dave he knows everything. Well Pete I am not sure. I know light comes from the sun but that’s all. Let me phone a friend. I’ll call John. Hey get me outta here, I’m too hip for this slide show!! Look Dave I have found some information you need. It is all very interesting indeed.

16. Light My calculations are completely wrong this time, but I did read in a book somewhere that light from the sun is a type of electromagnetic radiation and belongs to something called the electromagnetic spectrum. On this spectrum there are various kinds of electromagnetic waves with different wave lengths. These waves are known as Transverse waves. Look at this… Short wavelength (carry more energy) Long wavelength Cosmic rays X-rays Visible light Microwaves TV Gamma rays Ultraviolet Infra-red Radar Radio

17. Light Visible light Now are we going to do the prism trick? Okay, cool Roy.G.Biv. Here it is just as Sir Isaac Newton discovered in 1672. That means that white light contains all the colours of the spectrum!! It looks like a rainbow

18. Have you ever seen a rainbow without rain? When sunlight passes through a raindrop it bends or refracts and splits into colours

19. Light According to my calculations all colours hit different surfaces yet only some colours are reflected. We see that reflected colour or wavelength. The colours we don’t see are absorbed. All those colours are very lovely darling but why do we see them at all and not just white light?

20. Light That’s a tricky one my dear, but the answer is easy to remember as it is the opposite of white…which is… black, like the colour of your groovy suit. If white light contains all colours, what do you see if there is no colour reflected If I look at this leaf through a red filter, all the colour is absorbed and the leaf appears black. No colour is reflected. Cool!!

21. Light We can mix colours 2 ways. If we mixed coloured light we are adding the colours together so this is called addition. If you shine red, blue and green light together you can make white light. If we mix coloured dyes or paints, we make a mixture that absorbs all the colours, this is called subtraction. If I put enough different coloured paint on this canvas I will end up with black.

22. Light Mmm, that’s all very good, but what about light that doesn’t come from the sun? Good question. Well anything that gives off its own light is called luminous. If it emits light because it is hot it is said to be incandescent. If it doesn’t give off heat when it emits light it is said to be fluorescent. How about some examples: These are all incandescent other than the moon that reflects light to earth rather than produce it. Fluorescence can be seen in paint, the hand of watches, fire flies, deep sea creatures and glow worms.

23. Sound • Sound waves have some qualities different to light: • Sound waves are made as vibrations in objects around us. • The waves need to travel from place to place in solids, liquids or gases and will not be transmitted in a vacuum. • Sound generally travels faster through a solid than a liquid, and faster through a liquid than a gas! But how does sound work?

24. Sound Take these trumpeters for example. They blow into the trumpet causing a vibration along the hollow of the trumpet. The vibration escapes out the end of the trumpet and continues to vibrate in the air until it reaches our ear. Our ears are designed to pick up the vibration and convert it to a sound message our brain can understand.

25. Sound MMmmmm that means when we talk, our voices send vibrations across the air to another person. Cool! According to my calculations, sound waves travel much slower than light waves. In fact sound waves only travel at 330 meters per second in air, that is why we see the lightning before we hear the thunder!

26. Sound Rarefaction Compression One wavelength Sound waves are called compression (or longitudinal waves). You can think of sound waves like a big slinky!

27. Sound You may have noticed the strings on a guitar are thick and thin. The thin string gives a much higher pitched note because it vibrates quicker. A string will also vibrate quicker if it is pulled tight. Combining all the different pitched sounds the strings can make gives the guitar its sound. The same with a woman’s voice…her vocal cords are shorter and vibrate quicker giving her a higher pitched voice than a man. What I want to know is how music is made, how does this guitar work?

28. Sound According to my calculations, we need two ears to be able to know which direction sound is coming from…each ear compares the incoming sound and shares the information. But why do we have two ears?

29. & Light Sound Waves Okay so let’s summarise the properties of light waves and sound waves so I can get this straight in my head... Light waves Sound waves • Are compression (or longitudinal) waves • Need a medium (liquid, solid or gas) to travel in, won’t travel in a vacuum • Travel in air at speeds of about 330 m/s (depends on temperature) • Are transverse waves • Unable to travel through some substances, but can travel through a vacuum • Travel in air at speeds of about 300,000,000 m/s

30. Mmm I think that is all for now. See you in the lab! Yes my calculations state we have run out of time this lesson The End Cool! Bye. Can we do the prism thing again?