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WAVES

WAVES. WAVES. Diagram of a wave. All waves are caused by vibrations. PEAK OR CREST. WAVELENGTH. AMPLITUDE. TROUGH. WAVELENGTH. Frequency is the number of complete cycles or vibrations occurring every second. It is measured in HERTZ (Hz). 0s. 1s. 2 cycles in 1s = 2Hz. 0s. 1s.

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WAVES

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  1. WAVES WAVES

  2. Diagram of a wave All waves are caused by vibrations PEAK OR CREST WAVELENGTH AMPLITUDE TROUGH WAVELENGTH

  3. Frequency is the number of complete cycles or vibrations occurring every second. It is measured in HERTZ (Hz) 0s 1s 2 cycles in 1s = 2Hz 0s 1s 4 cycles in 1s = 4Hz

  4. LONGITUDINAL WAVE vibrations WAVE DIRECTION VIBRATIONS ARE PARALLEL TO WAVE DIRECTION

  5. TRANSVERSE WAVE vibrations WAVE DIRECTION VIBRATIONS ARE AT 90O OR RIGHT ANGLES TO WAVE DIRECTION

  6. Finding the relationship between WAVESPEED, FREQUENCY & WAVELENGTH 0s 0.5s 10m Frequency = 4Hz What is the relationship? Wavelength = 5 m Wavespeed = 20 m/s

  7. wave speed (m/s) = frequency (Hz) x wavelength (m) WS = F x WL F = WS WL WL = WS F WS F WL x

  8. 1. If the speed of a wave is 340m/s, and its wavelength is 20m, what is its frequency? wave speed = frequency x wavelength 340 = frequency x 20 frequency = 340 = 17 Hz 20

  9. If 300 cycles are produced in 60s and the wavelength is 10m, find:- • (a) the frequency • 300 cycles • 60s • (b) the wave speed • wave speed = frequency x wavelength = 5 cycles/s = 5 Hz = 5 x 10 = 50 m/s

  10. Light waves travel at 300 000 000 m/s. If their frequency is 500Hz, find their wavelength • wave speed = frequency x wavelength • 300 000 000 = 500 x wavelength • 300 000 000 = • 500 600 000 m

  11. If 25 cycles occur in 1 second and their wavelength is 3 metres, find the wave speed • wave speed = frequency x wavelength • = 25 x 3 • = 75 m/s

  12. WAVEFRONTS PEAK/CREST WAVELENGTH WAVEFRONTS (PEAK/CREST OF WAVES FROM ABOVE)

  13. Circular Wavefronts Each line is a peak/crest of a circular wave

  14. Diffraction of Waves Diffraction means spreading out. This can occur to waves when they go through a small gap.

  15. Diffraction (spreading out) of waves through a gap equal or smaller than the wavelength Spreading out Peaks or Crests of Waves

  16. Diffraction (spreading out) of waves through a gap larger than the wavelength Small amount of spreading out Peaks or Crests of Waves

  17. CONSTRUCTIVE INTERFERENCE Wave A Wave B Output

  18. INTERFERENCE DESTRUCTIVE Wave A Wave B Output

  19. Interference of Waves Wave A Wave B Resultant Wave

  20. Interference of overlapping waves Peak meets Peak or Trough meets Trough Constructive Interference

  21. Interference of overlapping waves Peak meets Trough Destructive Interference

  22. Reflection of light at a plane boundary e.g. mirror Incident Angle I Reflective Angle r Plane boundary e.g. mirror Incident Angle (i) = Reflected Angle (r)

  23. Reflection of wave fronts at a plane boundary Plane Boundary

  24. COMPARISON OF SPEED OF LIGHT THROUGH SOLIDS, LIQIDS AND GASES SOLID LIQUID GAS GLASS/PERSPEX WATER AIR SLOWEST FASTEST MOST DENSE LEAST DENSE

  25. REFRACTION OF LIGHT What happens to light when it changes speed AIR (LESS DENSE) A C GLASS/WATER (MORE DENSE) AIR B D (LESS DENSE) A When light travels from air into glass at an angle off the line of normal, (less dense to more dense), it slows down and bends towards the line of normal. BWhen light travels from glass to air at an angle off the line of normal, (more dense to less dense), it speeds up and bends away from the line of normal. C &DWhen light travels from air to glass or glass to air along the line of normal it does not change direction

  26. Refraction of wave fronts More dense substance (glass or water) Slow down – wavelength decreases Less dense substance (air) Speed up – wavelength increases

  27. Air Less Dense Glass/Water More Dense Total Internal Reflection and Critical Angle

  28. Refracts out into air and bends away from line of normal Less dense (AIR) boundary More dense (GLASS) Angle less than critical angle (angle less than 42o)

  29. Travels along boundary line between air and glass Less dense (AIR) boundary More dense (GLASS) Angle = critical angle (Angle = 42o)

  30. Totally internally reflected at same angle back into glass (boundary acts like a mirror) Less dense (AIR) boundary More dense (GLASS) Angle more than critical angle (Angle more than 42o)

  31. Angles A & B greater than critical angle of 42O Air B A Glass

  32. At A, B, C and D the angle is greater than the critical angle so the light gets totally internally reflected A B C D

  33. Fibre Optic Cable: used to send information as pulses of light Protective Cladding Glass Outer Covering

  34. Air (less dense) B D A C Glass (more dense) Air (less dense) At A, light enters glass, slows down and bends towards line of normal (refracts) At B & C, angle greater than critical angle, light gets totally internally reflected At D, angle less than critical angle so light leaves glass, speeds up and bends away from line of normal (refracts)

  35. Total Internal Reflection through a fibre optic cable

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