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Interference

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Interference

1. 1. Unit 1 - Waves <ul><li>Wave interference is the phenomenon which occurs when two waves meet while traveling along the same medium. </li></ul><ul><li>The interference of waves causes the medium to take on a shape which results from the net effect of the two individual waves upon the particles of the medium. </li></ul>Interference of Waves
2. 2. Unit 1 - Waves Interference of Waves
3. 3. Unit 1 - Waves <ul><li>Constructive interference is a type of interference which occurs at any location along the medium where the two interfering waves have a displacement in the same direction. If both waves have an upward displacement; the medium has an upward displacement which is greater than the displacement of the two interfering pulses. </li></ul><ul><li>Constructive interference is observed when a crest meets a crest; but it is also observed when a trough meets a trough. </li></ul>Interference of Waves
4. 4. Unit 1 - Waves Interference of Waves
5. 5. Unit 1 - Waves <ul><li>Destructive interference is a type of interference which occurs at any location along the medium where the two interfering waves have a displacement in the opposite direction. </li></ul>Interference of Waves
6. 6. Unit 1 - Waves <ul><li>When two pulses with opposite displacements (i.e., a crest and trough) meet at a given location, the upward pull of the crest is balanced (canceled or &quot;destroyed&quot;) by the downward pull of the trough. Once the two pulses pass through each other, there is still a crest and a trough heading in the same direction which they were heading before interference. </li></ul>Interference of Waves
7. 7. Unit 1 - Waves <ul><li>The two interfering waves do not need to have equal amplitudes in opposite directions for destructive interference to occur. For example, a crest with an amplitude of +1 unit could meet a trough with an amplitude of -2 units; the resulting displacement of the medium during complete overlap is -1 unit. </li></ul>Interference of Waves
8. 8. Unit 1 - Waves <ul><li>The meeting of two waves along a medium does not alter the individual waves or even deviate them from their path. </li></ul>Interference of Waves
9. 9. Unit 1 - Waves Interference of Waves
10. 10. Unit 1 - Waves <ul><li>The task of determining the shape of the resultant demands that the principle of superposition is applied. The principle of superposition is sometimes stated as follows: </li></ul><ul><ul><li>When two waves interfere, the resulting displacement of the medium at any location is the algebraic sum of the displacements of the individual waves at that same location. </li></ul></ul>Interference of Waves
11. 11. Unit 1 - Waves Superposition of Waves
12. 12. Unit 1 - Waves <ul><li>The amplitude and wavelength of interfering waves are often different. If conditions are controlled so that the waves have the same amplitude and wavelength, yet travel in opposite directions, the resulting interference pattern is referred to as a standing wave interference pattern. </li></ul>Standing Waves
13. 13. Unit 1 - Waves <ul><li>One characteristic of every standing wave pattern is that there are points along the medium which appear to be standing still. These points, sometimes described as points of no displacement, are referred to as nodes . </li></ul><ul><li>There are other points along the medium which undergo vibrations between a large positive and large negative displacement. These are the points that undergo the maximum displacement during each vibrational cycle of the standing wave. In a sense, these points are the opposite of nodes, and so they are called antinodes . A standing wave pattern always consists of an alternating pattern of nodes and antinodes. </li></ul>Standing Waves
14. 14. Unit 1 - Waves Standing Waves
15. 15. Unit 1 - Waves <ul><li>The nodes and antinodes in a standing wave pattern (like all the points along the medium) are formed as the result of the interference of two waves. </li></ul><ul><li>The nodes are produced at locations where destructive interference occurs. Nodes form at locations where a crest of one wave meets a trough of a second wave; or a half-crest of one wave meets a half-trough of a second wave; or a quarter-crest of one wave meets a quarter-trough of a second wave; etc. </li></ul>Standing Waves
16. 16. Unit 1 - Waves <ul><li>Antinodes are produced at locations where constructive interference occurs. For instance, if a crest of one wave meets a crest of a second wave, a point of large positive displacement results. Similarly, if a trough of one wave meets a trough of a second wave, a point of large negative displacement results. </li></ul><ul><li>Antinodes are always vibrating back and forth between these points of large positive and large negative displacement; this is because during a complete cycle of vibration, a crest will meet a crest; and then one-half cycle later, a trough will meet a trough. </li></ul>Standing Waves
17. 17. Unit 1 - Waves Standing Waves
18. 18. Unit 1 - Waves Wave Interference Lab