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Warm Up

Warm Up. Think back to our first day of this waves unit (Tuesday) when an object was dropped in the tub of water.... What do the waves you saw have in common with the waves of the electromagnetic spectrum?. What is a Wave?.

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Warm Up

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  1. Warm Up Think back to our first day of this waves unit (Tuesday) when an object was dropped in the tub of water.... What do the waves you saw have in common with the waves of the electromagnetic spectrum?

  2. What is a Wave? • Repeating disturbance or movement that carries energy through matter or space

  3. Mechanical Waves vs. Electromagnetic Waves • Mechanical Waves-can only travel through matter • Sound waves • Earthquake waves • Electromagnetic Waves- can travel through space • Radio, micro, and gamma waves etc.

  4. Two Basic Types of Waves we Study • Transverse Waves • Ocean Waves • Radio Waves • Light Waves • Heat Waves • Longitudinal Waves • Sound Waves • Some Earthquake Waves

  5. Transverse Waves • Move in an up and down motion at a right angle to the direction of the wave

  6. Parts of a Transverse Wave • Crest: highest point of the wave • Trough: lowest point of the wave

  7. Parts of a Transverse Wave cont’d Wavelength: () Distance between a point on one wave to the identical point on the next wave Amplitude: (a) Distance from the crest or trough of a wave to the resting point

  8. Longitudinal Wave • Matter vibrates in the direction of the wave • Examples: Sound waves, springs, coils

  9. How does a Longitudinal wave work? • Compressions expand to an area that is less dense • Rarefaction: The less dense area in a compressional wave

  10. How Does a Longitudinal Wave Work? (Cont’d) • Wavelength (): One compression and one rarefraction

  11. V  f Wave Speed • Velocity of a wave is calculated by multiplying wavelength by frequency Vw =  x f *As f increases,  decreases!

  12. Frequency Frequency – how many waves pass a point per unit of time. We usually measure frequency in Hertz (number of waves per second) What do you usually think of when you hear the term “Hertz”?

  13. Period (T) T=1/f Period is the amount of time it takes for 1 wave to pass

  14. Example Problem 1: • A wave is generated in a wave pool at an amusement park. The wavelength is 3.2 m and the frequency is 0.60 Hz. What is the velocity of the wave? V = x f 1.92 m/s

  15. Example Problem 2: • Earthquakes can produce three types of waves. One of these is a transverse wave called an “s” wave. A typical s wave travels at 5000 m/s. Its wavelength is 417 m. What is its frequency? • F = 12 Hz

  16. Example Problem 3: • A sound wave has a frequency of 500.0 Hz and a wavelength of 3.0 m. What is the speed of the wave? V = x f

  17. Example Problem 4 • The lowest-pitched sounds humans can hear have a frequency of 20.0 Hz. What is the wavelength of these sound waves if their wave speed is 340.0 m/s? V = x f

  18. Frequency and Pitch • Pitch: The highness or lowness of sound • Depends on the frequency • High frequency = high pitch • Low frequency = low pitch • 20,000 Hz: ultrasonic waves • 20 Hz and below: infrasonic waves

  19. Intensity and Loudness • Intensity: Energy of the wave • Loudness: Human perception of sound intensity. • Depends on the amplitude Decibel Scale (dB) - Measures intensity of sound

  20. How Loud? How High or Low? • Decibel Scale (dB) - Measures intensity of sound • Pitch – how high or low a sound seems to be • Depends on freqency • Higher f, higher the sound • Lower f, lower the sound • Ave range humans – 440 Hz – 7000 Hz • Ultrasonic - >100,000 Hz • Infrasonic – subsonic - <20 Hz

  21. Doppler Effect http://www.lon-capa.org/~mmp/applist/doppler/d.htm • Change in frequency due to a moving object • Sound moving and the observer is stationary

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