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Waves
 

Waves

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    Waves Waves Presentation Transcript

    • Waves
    • Slinky Waves A wave is caused by a vibrating source, and travels outwards from the source. The particles of the medium through which a wave travels move about their equilibrium positions; they do not move along with the wave. Energy is transferred from place to place by a wave.
    • To think about
      • Does the size of a pulse change as it travels along the spring? 
      • What is there was no friction?
      • What happens when a pulse reflects at the fixed end? (we need to clamp the slinky at one end)
      • How does the speed change if you change the tension? (does not work well, should be the same)
      • What happens if pulses set off from opposite ends at the same time?
    • What you are going to achieve today
      • By the end of the lesson you will know
      • What are the differences between transverse and longitudinal waves?
      • What is a plane-polarised wave?
      • What physical test can distinguish transverse waves from longitudinal waves?
      • What is meant by the amplitude of a wave?
      • Between which two points can the wavelength be measured?
      • How is the frequency of a wave calculated from its period?
      • What is phase?
    • Important wave diagram
    • Radians and waves
    • Phase Dual pendulums to demo phase
    • Phase Demo
    • Phase on the oscilloscope
    • V = f λ
      • V = velocity (m/s)
      • f = frequency (how many waves in a second)
      • λ = wavelength (m)
      λ c = f λ is used for electromagnetic waves as the velocity of light is always 3 x 10 8 m/s
    • All go at the speed of light
    • Speed, wavelength and frequency
      • 1)Light travels 300,000 km in one second.
      • a) How long does it take light to travel 300 m?
      •   b) How long does it take light to travel 300 mm?
      • 2)The speed of sound in a metal is 1000 m s–1.
      • a.) What is the wavelength if the frequency is 2 kHz?  
      •   b.) What is the wavelength if the frequency is 2 MHz?
      • 3)What is the frequency of sound waves of wavelength 100 mm?
      • 4)What is the frequency of radio waves of wavelength 100 mm?
      • 5)If you could 'freeze' ultrasound of wavelength 5 mm as it travels through tissue, how many waves would there be in a one metre length? This quantity is called the wave number . How is it related to wavelength?
      • 6)If a thunder clap comes 1.5 s after the lightning strike, how far away is the strike? Explain your calculation.
      The speed of sound in air 330 m/s speed of light 3 x 10 8 m/s. s = v ∆ t
    • Answers
      • 1 microsecond b) 1 nanosecond
      • 200 waves per metre; the wave number is the reciprocal of the wavelength.
      6) s = v ∆ t = 330 x 1.5 = 495 m, light transit time is negligible
    • Polarisation Polarisation can only happen with transverse waves http://www.youtube.com/watch?v=qlRriWu1zOI&feature=related http://www.youtube.com/watch?v=ozTH2zIKwC0&feature=player_embedded
    • 3D glasses
    • The water tubs waves in another medium
      • The speed of a water wave
      • Create a water wave at one end of the tub and
      • Time it to the other end
      • Change the depth of water
      • There should be a difference but it is very fast
      • Speed = √g x depth (metres)
      • Wave height  
      • (from trough to crest),
      • Wavelength (from crest to crest),
      • Period (time interval between arrival of consecutive crests at a stationary point),
      • The direction of wave propagation.
    • CHALLENGE! Demonstrate longitudinal and transverse waves In a group of 5 demo both types of wave