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Sound and Light Unit

Sound and Light Unit. Part 2: Characteristics of Waves. Objectives. Identify the crest, trough, amplitude, and wavelength of a wave Define the terms frequency and period Solve problems involving wave speed, frequency, and wavelength Describe the Doppler effect. Wave Properties.

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Sound and Light Unit

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  1. Sound and Light Unit Part 2: Characteristics of Waves

  2. Objectives • Identify the crest, trough, amplitude, and wavelength of a wave • Define the terms frequency and period • Solve problems involving wave speed, frequency, and wavelength • Describe the Doppler effect

  3. Wave Properties • Five main Properties that we are going to focus on: • Shape • Amplitude • Wavelength • Period • Frequency

  4. Wave Shape • An ideal transverse wave has the shape of a sine curve • A sine curve looks like an S lying on its side • Sine curves can be used to represent the other properties of waves as well.

  5. The Sine Curve of a Transverse Wave

  6. Amplitude • Measures the amount of particle vibration • It is the greatest distance that particles are displaced from their normal resting positions because of the wave • It is also half the vertical difference between a crest and a trough • A crest is the highest point of the wave • A trough is the lowest point of the wave • Larger waves have bigger amplitudes and carry more energy

  7. The Sine Curve of a Transverse Wave

  8. Longitudinal Waves • Do not have crests and troughs because they cause particles to move back and forth instead of up and down • A longitudinal wave is like a spring • The areas where the coils are bunched together are called compressions • The stretched out areas are called rarefactions • The amplitude of a longitudinal wave is the maximum deviation from the normal density or pressure of the medium

  9. Longitudinal Wave

  10. Wavelength • Wavelength is represent by the symbol lambda λand is measured in meters • It measures the distance between two equivalent parts of a wave • In a transverse wave it’s the distance between two consecutive crests or two troughs • In a longitudinal wave it’s the distance between two consecutive compressions or two rarefactions • Sound waves have very complicated shapes and sometimes vibrate irregularly

  11. The Sine Curve of a Transverse Wave

  12. Period • The time required for one full wavelength of a wave to pass by a certain point is called the period of the wave • It is also the time required for one complete vibration of a particle in a medium • It is represented by the symbol T and is measured in seconds

  13. Frequency • Measures the rate of vibrations • It is the number of wavelengths that pass a point in a given time interval • It also measures how rapidly vibrations occur in the medium, at the source of the wave, or both • The symbol for frequency is f and it is measured in hertz(Hz)

  14. Hertz • Named after Heinrich Hertz • In 1888, he became the first person to experimentally demonstrate the existence of electromagnetic waves • Hertz units measure the number of vibrations per second • One vibration per second is 1 Hz • You can hear sounds with frequencies as low as 20 Hz and as high as 20,000 Hz

  15. Did you Know? • Elephants communicate with low-frequency sounds that humans cannot hear • Their low-frequency calls travel much further than higher-frequency sounds • Under the right conditions, an elephant call can carry over thirty square kilometers or more! • Elephant families separated by several kilometers use the calls to coordinate their movements • Other animals that communicate with low-frequency sounds include blue and finback whales, hippos, and rhinos.

  16. Frequency & Period • Frequency and period are related • Frequency is the inverse of the period • The following equation is used to calculate:

  17. The Electromagnetic Spectrum • Light comes in a wide range of frequencies and wavelengths • Our eyes can detect light with frequencies ranging from about 4.3 x 1014 Hz to 7.5 x 1014 Hz • Light in this range is called visible light. • The differences in frequency in visible light account for the different colors we see

  18. The Electromagnetic Spectrum • Electromagnetic waves also exist at other frequencies that we cannot see directly • The full range of light at different frequencies and wavelengths is called the electromagnetic spectrum

  19. Wave Speed • Is equal to frequency times wavelength • It is simply how fast a wave moves • Wave speed is calculated using the following equations:

  20. Finding Wave Speed • An FM radio station broadcasts electromagnetic waves at a frequency of 94.5 MHz (9.45 × 107 Hz). These radio waves have a wavelength of 3.17 m. What is the speed of the waves? • f = 9.45 x 107 Hz λ = 3.17 m • v = ? • v = ƒ x λ • v = (9.45 x 107 Hz)(3.17m) • v = 3.00 x 108 m/s

  21. Influences on Wave Speed • The speed of a wave depends on the medium • Sound waves travel fastest in solids, then in liquids and slowest in gases. • Temperature also affects wave speed. • Sound travels faster through hot air than cool air.

  22. Kinetic Theory • Explains differences in wave speeds • The arrangement of particles in a medium determines how well waves travel through it • The different states of matter are due to different degrees of organization at the particle level

  23. Kinetic Theory with States of Matter • In gases, the molecules are far apart and move around randomly. • In liquids, the molecules are much closer together. But they are also free to slide past one another • In a solid, molecules are not only closer together but also tightly bound to each other

  24. The Speed of Light • Light has a finite speed • The speed of light is 3.00 x 108 m/s • Since the speed of light through space is a constant it is often represent by the symbol c

  25. The Doppler Effect • Is the apparent change in pitch as a sound passes by • The pitch of a sound is how high or low it is • Pitch is determined by the frequency at which sound waves strike the eardrum in your ear • A higher-pitched sound is caused by sound waves of higher frequency

  26. Wave Fronts • Suppose you could see the sound waves from the ambulance siren when the ambulance is at rest • You would see the sound waves traveling out from the siren in circular wave fronts • The distance between two successive wave fronts shows the wavelength of the sound waves • The sound waves have a frequency equal to the number of wave fronts that strike your eardrum each second • That frequency determines the pitch of the sound that you hear

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