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Behaviour of Waves

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  1. Behaviour of Waves Lesson 1: Types of Waves Lesson 2: Wave Speed Reflection Lesson 3: Refraction Total Internal Reflection Lesson 4: Refraction in Water Lesson 5: Refractive Index Lesson 6: Refraction in Water Lesson 7: Refractive Index Lesson 8: Diffraction Lesson 9: Transmitting Information Lesson 10: Sound

  2. Syllabus Double Award Properties of waves • describe longitudinal and transverse waves in ropes, springs and water where appropriate • state the meaning of amplitude, frequency, wavelength and period of a wave • recall that waves transfer energy and information without transferring matter • recall and use the relationship between the speed, frequency and wavelength of a wave: • wave speed = frequency × wavelength • v = f × λ • use the relationship between frequency and time period: • frequency = 1 / time period • f = 1 / T • use the above relationships in different contexts including sound waves and electromagnetic waves Light and sound • recall that light waves are transverse waves which can be reflected and refracted • recall that the angle of incidence equals the angle of reflection • construct ray diagrams to illustrate the formation of a virtual image in a plane mirror • describe experiments to investigate the refraction of light, using rectangular blocks, • semicircular blocks and triangular prisms • recall and use the relationship between refractive index, angle of incidence and angle of refraction • n = sin (i) / sin (r) • describe an experiment to determine the refractive index of glass, using a glass block • describe the role of total internal reflection in transmitting information along optical fibres and in prisms • recall and use the relationship between critical angle and refractive index • sin c = 1 / n • recall that sound waves are longitudinal waves which can be reflected • recall that the frequency range for human hearing is 20 Hz – 20 000 Hz • describe how to measure the speed of sound in air by a simple direct method

  3. Syllabus Separate Science Properties of waves • describe longitudinal and transverse waves in ropes, springs and water where appropriate • state the meaning of amplitude, frequency, wavelength and period of a wave • recall that waves transfer energy and information without transferring matter • recall and use the relationship between the speed, frequency and wavelength of a wave: • wave speed = frequency × wavelength • v = f × λ • use the relationship between frequency and time period: • frequency = 1 / time period • f = 1 / T • use the above relationships in different contexts including sound waves and electromagnetic waves • understand that waves can be diffracted through gaps or when they pass an edge, and that the extent of diffraction depends on the wavelength and the physical dimension of the gap Light and sound • recall that light waves are transverse waves which can be reflected, refracted and diffracted • recall that the angle of incidence equals the angle of reflection • construct ray diagrams to illustrate the formation of a virtual image in a plane mirror • describe experiments to investigate the refraction of light, using rectangular blocks, semicircular blocks and triangular prisms • recall and use the relationship between refractive index, angle of incidence and angle of refraction • n = sin(i) / sin(r) • describe an experiment to determine the refractive index of glass, using a glass block • describe the role of total internal reflection in transmitting information along optical fibres and in prisms • recall the meaning of critical angle c •  recall and use the relationship between critical angle and refractive index • sin c = 1 / n • understand the difference between analogue and digital signals • recall that sound waves are longitudinal waves which can be reflected, refracted and diffracted • recall that the frequency range for human hearing is 20 Hz – 20 000 Hz • describe how to measure the speed of sound in air by a simple direct method • understand how an oscilloscope and microphone can be used to display a sound wave • use an oscilloscope to determine the frequency of a sound wave and appreciate that the pitch of a sound depends on the frequency of vibration • appreciate that the pitch of a sound depends on the frequency of vibration of the source • appreciate that the loudness of a sound depends on the amplitude of vibration

  4. Types of Waves08/08/2014 Aims • To define the properties of waves • To identify the types of waves Starter: True or False Sound travels faster than light Sound travels faster in solid objects than in liquids or air Echoes are caused by sound waves bouncing of walls Sound waves are caused by the vibration of molecules Sound travels faster at the top of Mt. Everest Light waves bounce off walls

  5. A Wave • Waves transfer energy from one place to another • The disturbance moves along the wave not the particles

  6. A wave in the sea: • disturbance is molecules of water going up and down • medium = water

  7. A Mexican Wave • The Disturbance is the people going up and down. • The medium is the crowd.

  8. Frequency = 1 Hertz Count the number of complete vibrations in ten seconds and then work out the frequency of this wave Frequency = 1.4 Hertz Frequency = 0.5 Hertz Ten second timer

  9. Note that the waves are carrying energy from one place to another but the water particles are not transferred. next previous

  10. Frequency • Number of waves per second • Either passing one point or generated • Symbol: f • Units: Hz (s-1)

  11. Period • This is the duration of a wave • How long it takes for one wave to occur • Symbol: T • Units: s

  12. We often need to analyse waveforms produced by scientific instruments. For example:- A Cathode Ray Oscilloscope (CRO) is used to monitor heartbeats. Steady Steve 1 second Helen Heart-attack 0.5seconds David Deadman Heart monitor time

  13. Pictures of waves (waveforms) 1 mains voltage waveform 0.02 seconds 2.5milliseconds (0.0025seconds) 2 tuning fork 3 Ultrasonic scanner 10 micro seconds (0.00001 seconds) Work out the frequency for these 3 waveforms

  14. Which animals made these sounds? Pictures of waves (waveforms)

  15. 1 Cow 0.004 seconds 2 Baby crying 0.5milliseconds (0.0005seconds) 3 Bat 10 micro seconds (0.00001 seconds) Pictures of waves (waveforms)

  16. Wavelength

  17. Wavelength • The length of one complete wave • peak to peak or trough to trough • Symbol: λ • Units: m

  18. Which of the points is exactly one wavelength away from point A? Answer is E F B E G A C D The next 5 tasks will test to see if you have understood the idea of wavelength

  19. 1 Match the highlighted letter to one which is exactly one wavelength away from it. A B C D E F G H I J K L M N O P Q R S T U V W X

  20. 2 Match the highlighted letter to one which is exactly one wavelength away from it. A B C D E F G H I J K L M N O P Q R S T U V W X

  21. 3 Match the highlighted letter to one which is exactly one wavelength away from it. A B C D E F G H I J K L M N O P Q R S T U V W X

  22. 4 Match the highlighted letter to one which is exactly one wavelength away from it. A B C D E F G H I J K L M N O P Q R S T U V W X

  23. 5 Match the highlighted letter to one which is exactly one wavelength away from it. A B C D E F G H I J K L M N O P Q R S T U V W X

  24. Amplitude • maximum disturbance caused by a wave • measured from the middle to a peak or trough • symbol: a • units: m

  25. Questions about amplitude Match the waveforms to the sounds A B C F D 1 1 an echo 2 2 a crescendo 3 3 a weak regular heartbeat Click for answers 4 a strong regular heartbeat 4 5 a symbol being struck 5

  26. Transverse Waves

  27. Transverse Wave

  28. Transverse Wave • The disturbance is perpendicular to the direction of movement • Example Light

  29. Longitudinal Waves

  30. Longitudinal Waves • The disturbance is parallel to the direction of movement • Aka: pressure, compression waves • Example sound • Sketch on board

  31. Wave Behaviourrecap Aim • To define the properties of waves • To identify the types of waves

  32. Wave Speed08/08/2014 Aim: To calculate the speed of waves To Revise Reflection Starter: • Draw a transverse wave in rough and label the wavelength and amplitude • The frequency of a wave is 5 Hz what is it’s Period? (check back in your book if you need to)

  33. Wave speed • How fast the wave is travelling • Symbol v • Units m/s

  34. ENERGY speed VIBRATIONS The speed is how fast the disturbance travels (how fast the energy is transferred)

  35. speed ENERGY speed Notice that both waves have the same speed but different wavelengths and frequencies. The wave equation can explain this mathematically.

  36. Calculating the Speed of Wave Speed = Distance Time An explosion happens 1000m away and takes 3 seconds to reach you what is the speed of sound? Speed = Distance Time Speed = 1000 3 = 333 m/s

  37. Wave equation Wave speed, wavelength and frequency are related by the wave equation

  38. The Wave Equation The wave equation relates the speed of the wave to its frequency and wavelength: Wave speed (v) = frequency (f) x wavelength () in m/s in Hz in m V Worksheet  f

  39. Practice Questions: • Write out the variables (ie frequency = …) and the equations used • A water wave travels through a pond with a frequency of 5Hz and they are 10 m apart. How fast are they travelling? • Ricky hears a thunderclap that makes his ear drum vibrate at 165 Hz. The wavelength of the sound is 2 m how fast is the sound wave travelling? • Hannah sings an A, she knows the wavelength of the sound wave is 1.5m. How many times does her vocal chords vibrate per second? (hint: you need the answer to question 2) • Hannah plays another note on her guitar, the string vibrates with a frequency of 300 Hz what is the duration (the period) of each vibration of the string? • Jon has been running his heart is beating 180 times a minute. What is the frequency and period of his heart beats. • Jack throws a stone into the centre of a pond. The pond has a radius of 4m. He notices that it takes 2 seconds for the wave to reach the edge. He thinks the wavelength of the ripple is about 1m. What is the frequency of his ripple? What is the period of the ripple? • Purple light has a wavelength of around 6x10-7m. If its frequency is 5x1014 Hz what is the speed of light? • Red light travels at the same speed. Work out its frequency if its wavelength is about 4x10-7m.

  40. Reflection Angle of incidence = Angle of reflection Normal Reflected ray Incident ray Angle of reflection Angle of incidence Mirror Worksheet Movie

  41. Ultrasound generator high frequency electrical signal monitor Contact gel transducer Echoes are changed back into electrical signals. These are processed and imaged on the monitor changes the electrical signal into an ultrasonic pulse

  42. Ultrasound generator (4.5 months) monitor • speed of ultrasound inside the body • time for the ultrasound to travel • and partly reflected ultrasonic waves from • boundaries can be processed to produce an • image of the foetus Click to start the scan

  43. Wave Speedrecap Aim: • To calculate the speed of waves • To Revise Reflection

  44. Refraction 08/08/2014 Aims: To demonstrate refraction To explain the cause of refraction To observe total internal reflection Starter: Why does the magic trick of the Disappearing Coin work? Home