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Chapter 6

Chapter 6. WAVES Dr. Babar Ali. CHAPTER OUTLINE. CONCEPT OF WAVES. A wave is a disturbance that propagates through a system transferring energy Waves transfer E! (courtesy of Dr. Dan Russell, Kettering Univ.). WAVE PROPERTIES. Crest:. the highest point on a wave. Trough:.

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Chapter 6

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  1. Chapter 6 WAVES Dr. Babar Ali

  2. CHAPTER OUTLINE

  3. CONCEPT OF WAVES • A wave is a disturbance that propagates through a system transferring energy • Waves transfer E! (courtesy of Dr. Dan Russell, Kettering Univ.)

  4. WAVE PROPERTIES Crest: the highest point on a wave Trough: the lowest point on a wave Amplitude: maximum displacement in a wave height of crest or depth of trough Amplitude is related to the E of a wave

  5. WAVE PROPERTIES Wavelength (λ): distance between 2 successive crests Units = m or cm Frequency (f): # of waves produced per unit time. Units = 1/s = Hz Period (T): # of seconds per unit wave.

  6. WAVE SPEED • The speed of a wave can be calculated from its frequency (f) and wavelength (λ). f × λ = s • Units: Note, s = constant for a given wave

  7. Example 1: A sound wave has a speed of 344 m/s and a wave-length of 0.5 m. What is the frequency of this wave? f = ??? λ = 0.5 m s = 344 m/s f = 688 Hz

  8. Example 2: A sound wave has a speed of 344 m/s has a frequency of 20 kHz. What is this wave’s wavelength? f = 20 kHz λ = ??? s = 344 m/s λ = 0.017 m

  9. Example 3: An ocean wave passes a point on the pier at the rate of 12 waves per minute. What are the frequency and period of this wave? # of cycles = 12 time = 60 s f = ??? T = ??? f = 0.2 Hz T = 5 s

  10. LONGITUDINALWAVES • Waves where direction of particle movement is parallel to the direction of wave velocity, are longitudinal waves • Longitudinal waves have areas of high particle density (compressions) and of low particle density (rarefactions) • Sound is the most common example of a longitudinal wave.

  11. TRANSVERSEWAVES • Waves where the direction of particle movement is perpendicular to the direction of wave velocity, are transverse waves • i.e. mechanical waves, electromagnetic waves (light, microwave, x-rays, etc.)

  12. ELECTROMAGNETICWAVES • Electromagnetic waves (e&m waves) are transversewaves caused by vibrating electrons (e-) • Formed through interaction of electric and magnetic fields that are perpendicular to one another • In vacuum, e&m waves travel at the same speed and differ from each other only in freq.

  13. ELECTROMAGNETICSPECTRUM • The classification of electromagnetic waves according to their frequency is called electro-magnetic spectrum. • e&m waves range from γ rays (short λ , high f) to radio (long λ, low f)

  14. SOUND WAVES • Sound is the most common example of a longitudinal wave • In sound waves, the molecules of air transmit the vibrations through compressions and rarefactions • Sounds waves cannot travel in vacuum!

  15. SPEED OF SOUND • Speed of sound is affected by: • wind conditions, temperature, humidity and type of medium • NOT affected by its loundness (amplitude) • Sound travels faster in liquids and solids compared to gases • Closely packed molecules in solids and liquids will transmit the vibrations faster than in gases • Sound travels faster at higher T • Faster moving air particles bump into each other more frequently and carry vibrations in shorter time

  16. DOPPLER EFFECT • Pitch of a sound is the subjective measure of its frequency • High frequency sounds have high pitch, and low frequency sounds have low pitch • The apparent shift in pitch of sound when the source is moving relative to the observer is called the Doppler Effect • i.e. The sudden change in pitch of an ambulance siren as it goes by an observer is the result of the Doppler effect

  17. STANDING WAVES • Waves that are reflected on themselves and appear to “stand” are called standing waves • Standing waves produce the variety of sounds in musical instruments! (Animation) violin

  18. RESONANCE • Every object has natural vibrations caused by motion of its molecules • When a forced vibration matches an object’s natural vibrations, a dramatic increase in amplitude occurs  This phenomena is called Resonance • Some Examples • Tacoma Narrows Bridge • Resonant Bridge

  19. THE END

  20. Some Symbols Used •  all •  there is or there exists • D Change •  infinity •  multiplication •  proportional to •  less than or equal to •  greater than or equal to •  plus or minus •  degrees •  therefore • ≈ approximately equal to •  decreases •  increases • λ – Wavelength • E – Energy • H – Heat • # - Number • e- - electron • p+ - proton

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