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# Waves unit (1)

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### Waves unit (1)

1. 1. Waves Unit Waves, sound and light
2. 2. Waves and Vibrations <ul><li>A vibration is a movement that occurs in a period of time. </li></ul><ul><li>A wave is a movement that occurs in a period of time and also in space. </li></ul><ul><li>A wave is a way of transferring energy. </li></ul>
3. 3. Time for a Cycle <ul><li>The time that it takes for a wave (or vibration) to complete one cycle is called a period (T). </li></ul><ul><li>A cycle is when a process starts to repeat itself. </li></ul><ul><li>A period is measured in units of time (seconds, most of the time). </li></ul>
4. 4. Simple Harmonic Motion <ul><li>The swinging of a pendulum (or a mass bouncing on a spring), the motion back-and-forth, is called simple harmonic motion. </li></ul><ul><li>The result of this simple oscillation back-and-forth is a sine wave. </li></ul>
5. 5. Wave Characteristics <ul><li>There are some distinct parts of a wave called characteristics. </li></ul><ul><li>The peak is the top part of the wave. </li></ul><ul><li>The trough is the bottom part of the wave. </li></ul>
6. 6. More Characteristics <ul><li>The baseline is the line of 0 energy in the wave. </li></ul><ul><li>The wavelength (  )is the distance from peak to peak of the wave. </li></ul><ul><li>The amplitude is the distance from the baseline to the peak of the wave. </li></ul>
7. 7. More Characteristics <ul><li>Period (T) is the time that it takes for the wave to start over again, typically it is the time for one wavelength (  ) to pass by. </li></ul><ul><li>Frequency ( f )is the number of  to pass by in a time frame. </li></ul><ul><li>Frequency is measured in Hertz (Hz). </li></ul>
8. 8. Wave Speed <ul><li>It is calculated by dividing distance by time. </li></ul><ul><li>With a wave, it is no different, we just change some of the symbols </li></ul><ul><li>The velocity of a wave is calculated by dividing wavelength by period of the wave. </li></ul><ul><li>v =  / T or </li></ul><ul><li>v =  f </li></ul><ul><li>v = d / t </li></ul><ul><li>How is speed (velocity) calculated? </li></ul>
9. 9. Simple Calculations <ul><li>What is the speed of a wave that has a wavelength of 10.0 meters and it takes 2.0 seconds to go by? </li></ul><ul><li>The solution is: </li></ul><ul><li> = 10.0 m </li></ul><ul><li>T = 2.0 s </li></ul><ul><li>v =  / T </li></ul><ul><li>So, </li></ul><ul><li>v = 10.0 m / 2.0 s </li></ul><ul><li>v = 5.0 m/s </li></ul>
10. 10. <ul><li>What is the velocity of a wave that has a wavelength of 5.0 x 10 -3 meters and a frequency of 20.0 Hz? </li></ul><ul><li>The solution is: </li></ul><ul><li> = 5.0 x 10 -3 m </li></ul><ul><li>f = 20.0 Hz </li></ul><ul><li>v =  f </li></ul><ul><li>So, </li></ul><ul><li>v = (5.0 x 10 -3 m)(20.0 Hz) </li></ul><ul><li>v = 0.10 m/s </li></ul>
11. 11. <ul><li>What is the wavelength of a wave that travels at 4.00 m/s and has a period of 3.0 seconds? </li></ul><ul><li>The solution is: </li></ul><ul><li>v = 4.00 m/s </li></ul><ul><li>T = 3.0 s </li></ul><ul><li> = v T </li></ul><ul><li>So, </li></ul><ul><li> = (4.00 m/s)(3.0 s) </li></ul><ul><li> = 12 m </li></ul>
12. 12. <ul><li>What is the wavelength of a wave that travels at 200.0 m/s and has a frequency of 40.0 Hz? </li></ul><ul><li>The solution is: </li></ul><ul><li>v = 200.0 m/s </li></ul><ul><li>f = 40.0 Hz </li></ul><ul><li> = v / f </li></ul><ul><li>So, </li></ul><ul><li> = (200.0 m/s)/(40.0 Hz) </li></ul><ul><li> = 5.00 m </li></ul>
13. 13. <ul><li>What is the frequency of a pendulum if it swings back and forth with a period of 4.0 seconds? </li></ul><ul><li>The solution is: </li></ul><ul><li>T = 4.0 s </li></ul><ul><li>f = 1 / T </li></ul><ul><li>So, </li></ul><ul><li>f = 1 / (4.0 s) </li></ul><ul><li>f = 0.25 Hz </li></ul>
14. 14. <ul><li>What is the period of a wave if the wavelength is 20.0 m and the velocity is 10.0 m/s? </li></ul><ul><li>The solution is: </li></ul><ul><li> = 20.0 m </li></ul><ul><li>v = 10.0 m/s </li></ul><ul><li>T =  / v </li></ul><ul><li>So, </li></ul><ul><li>T = (20.0 m)/(10.0 m/s) </li></ul><ul><li>T = 2.00 s </li></ul>
15. 15. Types of Waves <ul><li>There are 2 basic types of waves. </li></ul><ul><li>One is called a longitudinal wave. </li></ul><ul><li>The other is called a transverse wave. </li></ul>
16. 16. Longitudinal Wave <ul><li>Longitudinal waves move the medium parallel to the motion of the wave. </li></ul><ul><li>Longitudinal waves are compression waves. </li></ul><ul><li>Longitudinal waves have the same characteristics as transverse waves. </li></ul><ul><li>However, peaks are referred to as condensations and troughs are rarefactions. </li></ul>
17. 17. Transverse Waves <ul><li>Transverse waves move the medium perpendicular to the motion of the wave. </li></ul><ul><li>Transverse waves are like ocean waves. </li></ul>
18. 18. A Different Type of Transverse Wave <ul><li>A different type of transverse wave is called the standing wave. </li></ul><ul><li>This is a wave that travels back and forth between 2 points. </li></ul><ul><li>N is called a node (null point). </li></ul><ul><li>A is called an anode (anti-null point). </li></ul>
19. 19. How do waves interact? <ul><li>When waves interact, it is called interference. </li></ul><ul><li>There are 2 types of interference. </li></ul><ul><li>Constructive interference </li></ul><ul><li>Destructive interference </li></ul>
20. 20. Constructive interference <ul><li>Constructive interference is when 2 or more waves come together and build themselves up. </li></ul><ul><li>They add their collective amplitudes together. </li></ul>
21. 21. Destructive interference <ul><li>Destructive interference is when 2 or more waves tear each other down. </li></ul><ul><li>They are off by “half a phase” and their amplitudes (peak and trough) subtract from each other. </li></ul>
22. 22. What happens if the interference keeps progressing? <ul><li>If the interference keeps going, then it is called resonance. </li></ul><ul><li>Resonance is when the waves keep building upon each other. </li></ul><ul><li>This occurs with constructive interference. </li></ul>
23. 23. What happens if the source of the wave is moving? <ul><li>If the source of the wave is moving, then the wave adjusts for the speed. </li></ul><ul><li>It compresses or expands depending on the direction the source is moving relative to the detector of the wave. </li></ul>
24. 24. Doppler Effect with Sound <ul><li>If the object isn’t moving, then the sound generated stays constant. </li></ul><ul><li>If the object is moving toward another object, then the sound is compressed. </li></ul><ul><li>This gives the sound a higher frequency and a higher pitch. </li></ul>
25. 25. <ul><li>If the source is moving away from the observer, then the sound is stretched out as it reaches the observer. </li></ul><ul><li>This gives the sound a lower frequency or a lower pitch. </li></ul>
26. 26. Doppler Effect with Light <ul><li>Similarly to sound, if the object is not moving, then the light emitted is normal. </li></ul><ul><li>If the source of the light is moving close to the speed of light, then the light is compressed and it is given a higher frequency (more energy). </li></ul>
27. 27. <ul><li>However, if the source of the light is moving away from the observer at nearly the speed of light, then it will have a stretched out wavelength and lower frequency (less energy). </li></ul><ul><li>This is also known as Red Shift. </li></ul>
28. 28. Light <ul><li>Light is known as an Electromagnetic wave. </li></ul><ul><li>But, light is also known as a photon. </li></ul><ul><li>Light is both a particle and a wave. </li></ul><ul><li>This is called the Duality of Light. </li></ul><ul><li>Light is a particle with a wave-like characteristic. </li></ul>
29. 29. More light <ul><li>Light does not need a medium to travel, neither do any of the EM waves. </li></ul><ul><li>Light travels at it’s own speed. </li></ul><ul><li>The speed of light is 3.00 x 10 8 m/s or 186,000 miles/sec. </li></ul><ul><li>Light travels in straight lines. </li></ul><ul><li>The photon is a packet of energy. </li></ul><ul><li>Einstein showed that light was a particle. </li></ul><ul><li>He was able to show that the momentum of the photon was able to move electrons, causing electricity to be produced. </li></ul>
30. 30. Waves Bounce <ul><li>When a sound wave bounces, we call it an echo. </li></ul><ul><li>When a light wave bounces, we call it a reflection </li></ul><ul><li>The law of reflection says that the reflected ray bounces off at the same angle, to the normal, as the incoming ray. </li></ul>
31. 31. Flat Mirror <ul><li>A flat mirror (flat surface) will reflect a true image. </li></ul><ul><li>This image will appear as if it were a copy of the original. </li></ul>
32. 32. Concave Mirror <ul><li>Concave mirrors follow the law of reflections. </li></ul><ul><li>Concave mirrors have the reflective surface on the inside of the curve. </li></ul>
33. 33. <ul><li>If an object is beyond the focal point of the concave mirror, then the image is smaller and inverted. </li></ul>
34. 34. <ul><li>If an object is within the focal point of the concave mirror, then the image is magnified. </li></ul>
35. 35. Convex Mirror <ul><li>A convex mirror has its reflective surface on the outside of the curve of the mirror. </li></ul><ul><li>Therefore, the focal point is inside the mirror, and the object of the reflection can not reach that focal point. </li></ul>
36. 36. <ul><li>Images seen in a convex mirror appear as smaller, right-side up, and the view is spread out more. </li></ul>
37. 37. Refraction <ul><li>Refraction is when a light wave travels through a medium and bends. </li></ul><ul><li>Whenever, light enters or exits a medium, the light rays bend. </li></ul><ul><li>A medium is a material that waves travel through. </li></ul>
38. 38. <ul><li>As the incoming light enters the medium at an angle, the medium bends that light according to its “index of refraction”. </li></ul><ul><li>This index is constant for each medium. </li></ul><ul><li>The different mediums also cause the light to change speeds. </li></ul>
39. 39. <ul><li>This bending of the light gives us the illusion that the objects are bent or in different locations when they are in water. </li></ul>
40. 40. Lenses <ul><li>Like mirrors, there are 2 different types of lenses. </li></ul><ul><li>A concave lens is curved so the open part is the inside of the curve. </li></ul>
41. 41. <ul><li>All lenses follow the same law of refraction. </li></ul><ul><li>Light bends as it goes through a lens. </li></ul>
42. 43. Convex Lens <ul><li>Convex lenses have the medium within the curve of the lens. </li></ul>
43. 44. <ul><li>Unlike the concave lens, which bends the rays outward, convex lenses bend the rays inward to a single point. </li></ul>
44. 47. The Electro-Magnetic Spectrum <ul><li>The electro-magnetic spectrum is also referred to as the EM spectrum. </li></ul><ul><li>This spectrum consists of waves that are driven by electric fields and magnetic fields that continuously create each other. </li></ul>
45. 48. <ul><li>Unlike other waves, the EM waves do not need a medium to propagate. </li></ul><ul><li>All EM waves (including light) travel at 3.0 x 10 8 m/s or 186,000 miles/second. </li></ul>