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Grade 11 Physics

Grade 11 Physics. Waves. The Nature of Waves. A wave is a travelling disturbance A wave carries energy from place to place. Wave Pulse. A single disturbance that travels through a medium A wave of short duration. https://phet.colorado.edu/en/simulation/wave-on-a-string. Periodic Waves.

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Grade 11 Physics

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  1. Grade 11 Physics Waves

  2. The Nature of Waves • A wave is a travelling disturbance • A wave carries energy from place to place

  3. Wave Pulse • A single disturbance that travels through a medium • A wave of short duration

  4. https://phet.colorado.edu/en/simulation/wave-on-a-string

  5. Periodic Waves • If the disturbance repeats itself regularly then a periodic wave is generated.

  6. Note • It is the disturbance that travels through the medium, not the medium itself.

  7. Important • Regardless of the nature of the wave (sound, slinky, water, etc) or the medium through which it travels (air, solid, liquid, etc.) all waves exhibit wave-like behaviour (interference, diffraction, refraction, etc.) and can be described using the same terminology (amplitude, wavelength, speed, etc.) and the same mathematical equations • When I use sound waves to demonstrate and illustrate the Doppler effect for example, it is not because only sound waves exhibit this effect. In fact all waves exhibit this effect. It’s just easiest to demonstrate it with sound waves.

  8. Here is the first exception … • Two basic types of waves: • If the disturbance is perpendicular to the direction of propagation of the wave it is called a transverse wave • If the disturbance is parallel to the direction of propagation of the wave it is called a longitudinal wave

  9. crest trough

  10. Periodicity • Examples: pendulum, rocking chair, engine cycle, Earth’s orbit, etc. • When talking about anything that repeats itself at regular time intervals we can define … • The Period T: The time for one complete cycle • The frequency f: The number of complete cycles per unit time • What is the relationship between these two?

  11. Example: Earth’s rotation • Period and frequency are reciprocals

  12. Assignment

  13. Speed of a wave • The speed of a wave depends on the physical properties of the medium • Examples: • Waves travel faster through stiffer springs • Speed of waves in water depends on the depth • Sound waves travel faster in warmer air

  14. Reflection • Fixed-end • Free end

  15. https://phet.colorado.edu/en/simulation/wave-on-a-string

  16. Reflection and Transmission • Occurs at the boundary where the speed of wave changes

  17. Interference • What happens when two waves meet? • Wave interference occurs when two waves act simultaneously on the same particles of a medium. There are two types of interference: constructive and destructive. • destructive interference occurs when a crest meets a trough resulting in a lower amplitude • Constructive interference occurs when pulses build each other up, resulting in a larger amplitude (crest meets a crest or trough meets a trough)

  18. https://www.geogebra.org/m/dJrTcxYd

  19. The Nature of Sound • Longitudinal wave that is created by a vibrating object • Sound wave consists of traveling pulses of high pressure zones, or condensations, alternating with travelling pulses of low pressure zones, or rarefactions • These pressure fluctuations are normally very small

  20. https://phet.colorado.edu/en/simulation/legacy/sound

  21. Sound requires a medium (gas, liquid, or solid) • Cannot exist in a vacuum

  22. The frequency of a sound wave • A sound with a single frequency is called a pure tone • Human hearing • You can hear sounds from 20 Hz to 20000 Hz (20 kHz) • Me…up to about 12 -14 kHz • Infrasonic (<20 Hz) Ultrasonic (>20 kHz) • Rhinos use infrasonic (down to 5 Hz) • Bats use ultrasonic (up to 100 kHz) • The brain interprets the frequency detected by the ear in terms of pitch

  23. High pitch corresponds to high frequency • Low pitch corresponds to low frequency

  24. The Speed of Sound • Sound travels through gases, liquids, and solids, at considerably different speeds • At room temp in air its approx 343 m/s • Moves 4 times faster in water • Moves 17 times faster in solids • Speed increases with temp • Air (0°C) 331 m/s • Air (20°C) 343 m/s

  25. Unless otherwise stated assume air at 20°C

  26. Natural Frequency • Nearly all objects when hit, struck, plucked, or strummed will vibrate • They tend to vibrate at a particular frequency (or set of frequencies) called the natural frequency • Some tend to vibrate at a single frequency (pure tone) like a flute or a tuning fork while others vibrate at a set of frequencies

  27. The natural frequency of an object is determined by its physical properties • Example: Guitar String • Linear density • Tension • Length https://www.nde-ed.org/EducationResources/HighSchool/Sound/frequencypitch.htm

  28. Dropped Pencil • 197 Hz • 211 Hz • 217 Hz • 219 Hz • 287 Hz • 311 Hz • 329 Hz • 399 Hz • Flute • 200 Hz • Tuba • 200 Hz • 400 Hz • 600 Hz • 800 Hz • 1000 Hz

  29. Forced Vibration • The tendency of one vibrating object to force another object into vibrational motion • A louder sound is always produced when an accompanying object of greater surface area is forced into vibration • Examples • Wooden body of a guitar • Sounding board in a piano

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