1. Physics Day 37 Waves LO: Calculate wave Speed LO: Constructive & Destructive Interference LO: Superposition of waves AGENDA Do Now Notes Worksheet Homework HW14 Thursday Do Now: Waves have a frequency 2 Hz and wavelength 20 meters. What is the wave speed?

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

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

6. Wave A Wave B Output CONSTRUCTIVECONSTRUCTIVE INTERFERENCEINTERFERENCE

7. Wave A Wave B Output DESTRUCTIVEDESTRUCTIVE INTERFERENCEINTERFERENCE

8. Wave A Wave B Resultant Wave Interference of Waves

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

10. Peak meets Trough Destructive Interference Interference of overlapping waves

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

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

14. SOLIDLIQUIDGAS GLASS/PERSPEXWATERAIR SLOWESTFASTEST MOST DENSE LEAST DENSE

15. AIR GLASS/WATER AIR (LESS DENSE) (MORE 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. A B B When 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 D C & D When light travels from air to glass or glass to air along the line of normal it does not change direction What happens to light when it changes speed (LESS DENSE)

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

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

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

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

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

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

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

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

25. A B C D Air (less dense) Glass (more 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)

26. Total Internal Reflection through a fibre optic cable

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

29. 0s 1s 0s 1s Frequency is the number of complete cycles or vibrations occurring every second. It is measured in HERTZ (Hz) 2 cycles in 1s = 2Hz 4 cycles in 1s = 4Hz

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

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

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

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

34. 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

35. 2.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

36. 3.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

37. 4. 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

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

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

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