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4.1 – Properties of Waves

4.1 – Properties of Waves. 4.1 – Features of a Wave. To study optics, some starting vocabulary is needed Wave A disturbance or movement that transfers energy through matter or space, without causing any permanent displacement Energy

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4.1 – Properties of Waves

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  1. 4.1 – Properties of Waves

  2. 4.1 – Features of a Wave • To study optics, some starting vocabulary is needed • Wave • A disturbance or movement that transfers energy through matter or space, without causing any permanent displacement • Energy • The capacity to apply a force over a distance, or the ability to perform work • Force • A push or a pull on an object

  3. 4.1 – Features of a Wave • The dotted line represents the equilibrium or rest position • Remember from section 1.3 • An equilibrium is a balance in a system between opposing forces or quantities, like concentration of height

  4. 4.1 – Features of a Wave • Notice the new terms: • Crest • The highest point in a wave • Trough • The lowest point in a wave

  5. 4.1 – Features of a Wave • One of the most important properties of waves is its amplitude • Amplitude • The height of a crest or the depth of a trough, measured from the equilibrium position

  6. 4.1 – Features of a Wave • Another important property of waves is its wavelength • Wavelength • The distance from one crest to the next, or one trough to the next • Also the distance to complete one crest and one trough

  7. 4.1 – Features of a Wave • Another important property of waves is its frequency • Frequency • The number of repetitive motions that occur in a given time

  8. 4.1 – Features of a Wave • Amplitude • The units of amplitude depend on what kind of wave it is • Sound  decibels (dB) • Light  volts per meter (V/m) • Wavelength • Measured in metres (millimetres, micrometres, etc.) • Frequency • Measured in: • Hertz (Hz) • The number of cycles per second

  9. 4.1 – Features of a Wave • Frequency and wavelength have an inverse relationship • Inverse relationship (inversely proportional) • When one value increases as the other decreases • As the wavelength increases, the frequency decreases

  10. 4.1 – Features of a Wave • Frequency, wavelength and amplitude relate to properties we recognize • Frequency and wavelength • The colour of visible light • Red  400 – 484 THz • Blue  668 – 789 THz • The pitch of sound • C4 (middle C)  261.6 Hz • C5  523.3 Hz

  11. 4.1 – Features of a Wave • Frequency, wavelength and amplitude relate to properties we recognize • Amplitude • A higher amplitude means the wave carries more energy • How bright a light is • The higher the amplitude, the brighter the light • The volume of sound • Softest sound you can hear  0 dB • Breathing  10 dB • Typical library  40 dB • Typical conversation  50 – 60 dB • Busy street  90 dB • Typical concert  120 – 150 dB • Eardrum rupture  >175 dB

  12. 4.1 – Two Types of Waves • Most types of waves require something to travel through • Medium • The matter (a solid, liquid, gas or combination of these) that a wave travels through • Sound waves  medium is air • Ocean waves  medium is water • Not all waves require a medium • Light travels the fastest through a vacuum • Different types of waves interact differently with a medium (section 4.2) • Sound speeds up as the medium gets denser • Light slows down as the medium gets denser

  13. 4.1 – Two Types of Waves • Cherenkov radiation • When light travels through water, it does so at 75% of its maximum speed • Electrons in the water can therefore travel faster than the slowed-down light, producing this blue glow

  14. 4.1 – Two Types of Waves • Type 1 • Transverse wave • A wave in which the matter of the medium moves up and down, at 90 degrees to the direction of wave travel • Examples • Flicking a rope up and down • Light waves • “The Wave” • Think about it – the wave moves left or right, but you move up and down

  15. 4.1 – Two Types of Waves • Type 2 • Compression wave • A wave in which the medium moves back and forth along the same direction that the wave travels • Example • Sound • Air compresses and expands, pushing sound energy through the air

  16. 4.1 – Two Types of Waves • Earthquakes feature both types of waves • P waves (primary waves) • Compression waves • Can travel through any medium • Travel the fastest, so they arrive first • S waves (secondary waves) • Transverse waves • Can only travel through solids • Travel slower than P waves, so they arrive second

  17. Pg 142 – Active Noise Cancellation • Multiple waves can overlap • When they do, their amplitudes add together • Amplitudes above the equilibrium are positive • Amplitudes below the equilibrium are negative • We can use this • Noise cancelling headphones have a microphone and a signal processor • The microphone measures the background noise • The signal processor analyzes the signal and identifies the positive sound wave • The sound that is heard, but will be blocked

  18. Pg 142 – Active Noise Cancellation • The headphone speakers then produce another sound wave that has the complete opposite shape of the positive wave • This is called the negative wave • The positive and the negative waves cancel each other out

  19. 4.1 – Properties of Waves • Homework break #1 • Reading Check • Pg 138, #1-5

  20. 4.1 – Properties of Waves

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