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Waves

Waves. Waves transfer ENERGY. Wave speed can be calculated from Speed = distance / time. Radio and TV waves travel at the speed of light through air : 3.0 x 10 8 ms -1. Speed of sound through air. TSA. Measure the time the sound takes to travel a measured distance. A. B. 1 m.

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Waves

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  1. Waves Waves transfer ENERGY. Wave speed can be calculated from Speed = distance / time. Radio and TV waves travel at the speed of light through air : 3.0 x 108 ms-1

  2. Speed of sound through air TSA Measure the time the sound takes to travel a measured distance. A B 1 m Clap at microphone 1, this starts the timer. The sound travels through the air to microphone 2 and stops the timer. Use speed = distance / time.

  3. Wave Terms • Wavelength, λ, is the distance between identical points on adjacent waves • Frequency, f, No of waves that pass a point in 1 second. Units : Hertz, Hz. • Period, T, Time for 1 wave to pass. Units, seconds, s. • T =- 1 / f • Amplitude,a , Height of wave from centre to crest. Measure of energy transferred. Units, metres, m.

  4. Transverse Wave • This is a transverse wave, The particles vibrate at 900 to the direction of energy transfer. • Water waves • Light Waves a λ

  5. Longitudinal Wave • Particles vibrate in the same direction as energy transfer. • Sound Waves

  6. Wave Equations v = f . λ Speed = frequency x wavelength d = v . t Distance = speed x time

  7. Calculate how long it takes sound traveling at 340 m s-1 to travel from Dunfermline to Falkirk, 30 km away. v = 340 m s-1 d = 30 km = 30000 m t= ? d= v x t t = d / v = 30000 / 340 = 88.2 s

  8. Radio 1 transmits on a frequency of 96.8 MHz. Calculate the signal wavelength. v = 3.0 x108 ms-1 f = 96.8 x106 Hz λ = ? v = f x λ 3.0 x108 = 96.8 x106 x λ λ = 3.1 m

  9. Reflection • All waves can be reflected • normal

  10. Principle of reversibility • If the ray travels in along the path of the reflected ray it comes out along the path of the incident ray.

  11. Curved Reflectors • The signal is collected over a large are and reflected to a focus. The aerial is situated at the focus. E.g satellite receivers for SKY TV.

  12. Curved Reflectors 2 • If a bulb is placed at the focus of a curved reflector the light that is reflected of the reflector is focussed into a parallel beam. • Satellites use reflectors to direct the signals to specific parts of the country.

  13. Total Internal Reflection • When the angle of incidence is greater than a critical angle,θc, the light is totally internally reflected. Note at θc the angle of reflection is 900

  14. Total Internal Reflection 2 • Light travels down fibre optic cables via total internal reflection,

  15. Fibre Optic sytems • At phone, Es to Ee in microphone • Ee to El in laser • Light signal transmitted down fibre optic cables • El to Ee at photodiode • Ee to Es at loudspeaker

  16. Total Internal Reflection • Diamonds sparkle because the light is totally internally reflected lots of times before passing out into the air again.

  17. Refraction • The change of speed when light travels from one medium to another. • Light slows down when it enters a material from air.

  18. Refraction 2 • If the light goes in at an angle other than 900 it changes direction. • Slows down, bends towards the normal. • Speeds up bends away from the normal.

  19. Converging Lens ( Convex ) • Parallel rays of light are brought to a focus

  20. Diverging or Concave Lens • Parallel ray so flight are diverged

  21. Short sight • Close up objects are in focus but distant objects are blurred • A concave lens is placed in front of eye. Parallel rays from distant object

  22. Long Sight • Distant objects are in focus but close up objects are blurred. • A convex lens is placed in front of the eye Diverging rays from close up object

  23. Power and Focal Length • Power = 1/ focal length • Dioptres, D , Metres , m

  24. Ray Diagrams • Object greater than two focal lengths. E.g. image formed on retina of eye. Image is laterally inverted, diminished and upside down

  25. Ray Diagrams 2 • Object between 1 and 2 focal lengths e.g. image formed on cinema screen. Image is laterally inverted , upside down and magnified

  26. Ray Diagrams 3 • Object closer than focal length i.e. magnifying glass. Image is upright and magnified ,it is a virtual image.

  27. Diffraction This is the ‘bending of waves as they pass an obstacle or pass through a gap. The greater the wavelength the greater the amount of diffraction. Low frequency ( big wavelength )radio signals can be picked up in hilly areas yet high frequency( small wavelength ) TV signals cannot diffract into the valleys.

  28. Diffraction 2 BBig wavelength :a large amount of diffraction Big wavelength :a large amount of diffraction • A

  29. Diffraction 3 SmSmall wavelength :a small amount of diffraction small wavelength :a small amount of diffraction • B

  30. BIG wavelength wavelengthRadio waves Small wavelengthall wavV Small wavelengthwaveslength TV waves not received V waves not received Radio waves Receivedreceivedio waves received OK

  31. Sound Sound is a form of . It travels by which need a MEDIUM or substance to move through. It CANNOT travel through a Sound travels via a transverse wave. Sound levels are measured in decibels (dB). ENERGY WAVES VACUUM.

  32. Earpieces Open Bell Rubber Tube Closed Bell Sound Stethoscope This is an instrument used to “listen” to sounds inside our bodies.

  33. UltraSound Ultrasound This is sound with a frequency higher than the limit of human hearing, ie above 20kHz (20 000Hz). It has two main uses in medicine ~

  34. Sound Ultrasound Imaging A transmitter sends high frequency sound waves into the patient. The waves reflect from different types of tissues and are detected by a receiver as they come back out. The data is processed by a computer and the “ultrasound image” is displayed. It is a useful method for looking at unborn babies in their mothers womb as it has no known side effects.

  35. UltraSound Ultrasound Image of Unborn Baby

  36. UltraSound Breaking Up Kidney Stones High energy ultrasound is directed very accurately at kidney stones (hard material “stuck” inside a patients kidney ~ forms into a small stone). The ultrasound vibrations cause the stones to break up into dust and they pass out of the body by normal means. This means no need for open surgery.

  37. Sound ; Pollution Noise Pollution Our “hearing” is very sensitive and can easily be permanently damaged by excessive noise. Noise pollution is simply “excessive noise” and can come from factories, building sites, heavy motor vehicles (tractors, JCB’s), aircraft etc. Sometimes we endanger our own hearing by using MP3 players, going to rock concerts and discos.

  38. Sound ; Pollution Jet on take off Rock Band Passing JCB Vacuum Cleaner Living Room “music” Normal Conversation Morning Bird Song Whisper Threshold of Hearing

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