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Topic 11 – Wave Phenomena

Topic 11 – Wave Phenomena. 11.1 – Standing/ Stationary Waves. Standing Waves. Formation of standing waves Standing waves are formed when two identical waves meet each other travel in opposite directions. Wiki – Waves on a string

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Topic 11 – Wave Phenomena

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  1. Topic 11 – Wave Phenomena 11.1 – Standing/ Stationary Waves

  2. Standing Waves • Formation of standing waves Standing waves are formed when two identical waves meet each other travel in opposite directions. Wiki – Waves on a string • The result of this is a wave where the peaks simply move up and down but DO NOT PROGRESS.

  3. Standing vs Progressive Waves

  4. Formation of Standing Waves

  5. Formation of Waves in Closed Pipes

  6. Formation of waves in open pipes

  7. 11.2 Doppler Effect • The change in pitch of a sound wave due to a change in frequency of the wave is called the Doppler Effect. • It is caused by the relative motion of the SOURCE and the DETECTOR

  8. Moving Source

  9. Moving Observer

  10. Doppler Effect and EM radiation • The EM spectrum travels at c through a vacuum but if the velocity of the observed EM radiation in a lot smaller than c then we can use the following equation to calculate the change in frequency For v << c

  11. Doppler Effect Equations

  12. Using the Doppler Effect! • 11.2.6 – Outline an example in which the Doppler Effect is used to measure speed.

  13. 11.3 Diffraction • A more in depth look at diffraction • Huygens’ Principle • http://www.acoustics.salford.ac.uk/feschools/waves/diffract3.php

  14. Diffraction from a single slit • What is the diffraction pattern shown on a screen when a wave is diffracted around a single slit?

  15. Explaining the diffraction pattern

  16. Explaining the diffraction pattern

  17. Explaining the diffraction pattern

  18. Explaining the diffraction pattern

  19. Explaining the diffraction pattern

  20. 11.4 Resolution • If two sources sources of light are very close in angle to each other they can sometimes be seen as one light source. • If we can detect that there are two light sources then we say the light sources are resolved • The ability to do this depends on the RAYLEIGH CRITERION

  21. Rayleigh Criterion

  22. Rayleigh Criterion • If the sources are to be just resolved, then the minimum of one diffraction pattern is located on top of the maximum of the other diffraction pattern. • For a SLIT – the minima was located at • For a CIRCULAR APERTURE -

  23. Importance of Resolution Research the importance of resolution in the development of the following technologies • CDs • DVDs • Electron Microscope • Radio Telescopes

  24. Intensity • Def’n– Power incident on a unit area • (simply put – the greater the intensity the brighter the light will be) • Intensity = Power/ Area • Units = ?? • IMPORTANT – There is a squared relationship between intensity and amplitude of the wave • Intensity is proportional to the amplitude squared

  25. 11.5 Polarisation • If a wave is restricted to travel in one plane only, we say it is polarised. • Here the wave is forced to travel in the vertical direction. It can pass through the first slit but cannot pass through the horizontal slit. We say it is polarised in the vertical plane. • Looking at this… Can all types waves be polarised?

  26. Effect of Polarisers on intensity • Polarisation Sim on wiki • If unpolarised light passes through a set of polarising filters what is the effect on the intensity of the transmitted wave?

  27. MALUS LAW Key Words – Polariser and Analyser

  28. Malus’ law

  29. MALUS’ Law Remember the importance of the squared proportionality relationship between Intensity and Amplitude

  30. Polarisation by reflection • When light is reflected from a surface, the reflected ray becomes polarised in the plane of the surface. • The amount of polarisation depends on the angle of incidence. • 100% polarisation occurs when the angle of incidence is equal to the Brewster’s angle.

  31. Brewster’s angle

  32. Brewster’s angle

  33. Optically active substances • Optically active substances rotate the plane of polarisation of the light passing through them. • Examples include – sugar solutions, some plastics (when stressed) • With sugar solutions the concentration of the solution changes the amount of rotation. This can be used to determine the concentration on solutions • http://www.chemguide.co.uk/basicorg/isomerism/polarised.html

  34. Optically Active Substances

  35. Uses of polarisation • Polaroid Sunglasses • LCD screens • Stress Analysis

  36. Problems Questions 28-31 in your textbook!

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