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WAVES

WAVES. Newtonian Question c=f* λ f=1/T. An electromagnetic wave travels from Atlanta to L.A. in 0.02154 s (one complete cycle). How far is L.A. from Atl. in Kilometers? (all EM waves travel at 3.0*10^8 m/s; 1000 m=1km) A) 6,462,000 km B) 1.39*10^10 km C) 1.39*10^7 km D) 6,462 km.

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WAVES

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  1. WAVES

  2. Newtonian Questionc=f*λ f=1/T • An electromagnetic wave travels from Atlanta to L.A. in 0.02154 s (one complete cycle). How far is L.A. from Atl. in Kilometers? (all EM waves travel at 3.0*10^8 m/s; 1000 m=1km) • A) 6,462,000 km • B) 1.39*10^10 km • C) 1.39*10^7 km • D) 6,462 km

  3. The Doppler Effect • The apparent change in frequency due to the motion of the source of a wave (or its receiver) is called the Doppler Effect • Blue Shift – Increase in frequency • Red Shift – Decrease in frequency

  4. The Doppler Effect

  5. The Doppler Effect

  6. The Doppler Effect

  7. What is a wave? A wave • is caused by a vibration • is a wiggle in space and time • carries energy not matter

  8. 1st Major Category Mechanical Waves • waves that require a medium (solid, liquid, or gas) through which to travel. • Speed of the waves depends on the elasticity of the medium • Are governed by Newton’s Laws • 3 types of mechanical waves: transverse, longitudinal, and surface

  9. Types of mechanical waves • Transverse wave- particle displacement is perpendicular to the wave motion • Examples include waves in piano and guitar strings

  10. Types of mechanical waves (cont) • Longitudinal waves- particle displacement is parallel to the wave motion • Sound is a longitudinal wave • Fluids, liquids, gases, and plasmas usually only transmit longitudinal waves

  11. Types of mechanical waves (cont) • Surface waves- a combination of both transverse and longitudinal waves • Waves on the water’s surface are examples of surface waves

  12. Properties of mechanical waves* Crest- the high point of a wave Trough- the low point of a wave Amplitude- measurement of the amount of energy the wave carries *Some properties are only found in transverse waves and some properties are only found in longitudinal waves.

  13. Properties of mechanical waves* (cont) Wavelength- the distance between the midpoint of one crest/trough to the midpoint of the next crest/trough Line of equilibrium- the resting point of a wave

  14. Draw the first type of mechanical wave, a transverse wave, and label the crest, trough, wavelength, amplitude, and line of equilibrium

  15. Check your answer!

  16. Draw the second type of mechanical wave, a longitudinal wave, and label the compression, rarefaction, and wavelength.

  17. Check your answer!

  18. Velocity of mechanical waves • Calculated using the formula • V = fλ • Where v is velocity, f is frequency, and λ (Greek letter lamda)is wavelength. • Other variations: • f = V / λ • λ = V / f

  19. Other relevant formulas • T = 1/f • f = 1/T • Where T is the period and f is frequency • Frequency is measured in HERTZ • Hertz are literally per-seconds • How ever many waves pass a certain point PER SECOND is the frequency.

  20. Solve the following problem • Problem: Calculate the velocity of waves in water that are 0.4 m apart and have a frequency of 2 Hz.

  21. Answer: • v = fλ • v = (2 Hz)(0.4 m) • v = 0.8 m/s

  22. One more try! • Problem: What is the wavelength of a 340 Hz sound if the velocity of sound is 343 m/s?

  23. Answer: • v = fλ • 343 m/s = (340 Hz)λ • ~1.0 m = λ

  24. Wave Interference • Waves have a very unique property, they can occupy the same space at the same time. • This phenomenon is called interference! • Interference can be either constructive or destructive.

  25. Wave Interference (Cont) • Constructive interference, or reinforcement, occurs when the crests of two waves overlap each other and the amplitudes are added together.

  26. Wave Interference (cont) • Destructive interference, or cancellation, occurs when a crest and a trough of two waves overlap and their amplitudes cancel out.

  27. 2nd Major Category • Electromagnetic waves • Wave does not need a medium to travel • Wave that is partly electric and partly magnetic • All EM waves are located on the electromagnetic spectrum • All EM waves travel at the speed of light (3.0 x 108 m/s)

  28. The Electromagnetic Spectrum

  29. Solving an EM problem • The velocity for all EM waves is 3.0 x 108 m/s and is represented by the letter c. • Therefore, the equation v =fλ becomes c = fλ!

  30. Solving an EM problem (cont) • Problem: The wavelength of yellow light is 556 nm. What is the frequency? • Answer: c = fλ 3.0 x 108 m/s = f(556 nm) 5.4 x 1014 Hz

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