1. Do now! Can you discuss with your partner all the things you can remember about the WAVES topic (topic 3)

2. Topic 3 Waves

3. Waves Waves can transfer energy and information without a net motion of the medium through which they travel. They involve vibrations (oscillations) of some sort.

4. Rays Rays highlight the direction of energy transfer.

5. Transverse waves The oscillations are perpendicular to the direction of energy transfer. Direction of energy transfer oscillation

6. Transverse waves peak trough

7. Transverse waves Water ripples Light On a rope/slinky Earthquake

8. Longitudinal waves The oscillations are parallel to the direction of energy transfer. Direction of energy transfer oscillation

9. Longitudinal waves compression rarefraction

10. Longitudinal waves Sound Slinky Earthquake

11. Wave measurements

12. Amplitude - A The maximum displacement from the mean position. amplitude

13. Period - T The time taken (in seconds) for one complete oscillation. It is also the time taken for a complete wave to pass a given point. One complete wave

14. Frequency - f The number of oscillations in one second. Measured in Hertz. 50 Hz = 50 vibrations/waves/oscillations in one second.

15. Period and frequency Period and frequency are reciprocals of each other f = 1/TT = 1/f

16. Wavelength - λ The length of one complete wave. wavelength

17. Wave speed - v The speed at which the wave fronts pass a stationary observer. 330 m.s -1

18. The Wave Equation The time taken for one complete oscillation is the period T. In this time, the wave will have moved one wavelength λ. The speed of the wave therefore is distance/time v = fλ v λ f x

19. 1)A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is it moving? 2)A water wave travels through a pond with a speed of 1m/s and a frequency of 5Hz. What is the wavelength of the waves? 3)The speed of sound is 330m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound? 4)Purple light has a wavelength of around 6x10 -7 m and a frequency of 5x10 14 Hz. What is the speed of purple light? Some example wave equation questions 0.2m 0.5m 0.6m/s 3x10 8 m/s

20. Electromagnetic spectrum Long Wavelength Short Wavelength Low Frequency High Frequency

21. What do they all have in common? They can travel in a vacuum They travel at 3 x 10 8 m.s -1 in a vacuum (the speed of light) They are transverse They are electromagnetic waves (electric and magnetic fields at right angles to each oscillating perpendicularly to the direction of energy transfer)

22. Light travels faster than sound Speed of light = 300 000 000 m/s Speed of sound (in air) = 330 m/s Can you copy this please?

23. Law of Reflection normal Angle of incidence Angle of reflection mirror angle of incidence = angle of reflection Can you copy please?

24. Image in a mirror Upright Same size as object Distance from mirror to object = “distance” from image to mirror Laterally inverted

25. Why?

26. Refraction Glass block Beam of light Light going from air to glass bends towards the normal Light going from glass to air bends away the normal Can you copy this please?

27. Refraction When a wave changes speed (normally when entering another medium) it may refract (change direction)

28. Snell’s law i r Ray, NOT wavefronts speed in substance 1 = sin(i) speed in substance 2 sin(r)

29. Snell’s law i r Ray, NOT wavefronts In the case of light only, this quantity is called the refractive index (η) η = sin(i) sin(r)

30. Critical Angle Critical angle (when angle of refraction is 90º) Copy! 90º

31. Total Internal Reflection Critical angle sin c = 1/η sin(critical angle) = 1/(refractive index)

32. Examples of Total Internal Reflection

34. Diffraction Waves spread as they pass an obstacle or through an opening

35. Diffraction Diffraction is most when the opening or obstacle is similar in size to the wavelength of the wave

36. Diffraction Diffraction is most when the opening or obstacle is similar in size to the wavelength of the wave

37. Analogue and digital Let’s read pages 164 and 165.

38. 10 4 10 3 10 2 10 1 10 0 10 -1 10 -2 10 -3 15 2525 2424 23232 2121 2020 2 -1 2 -2 2 -3 1111

39. 01111001101111001101111011101 111 70111 91001 111011 121100 131101 141110 1110 151111 1111 1111

40. Advantages of digital signals Less affected by interference Interference is not increased when the signal is amplified Uses weaker signals than analogue.

41. Sound Longitudinal waves The oscillations are parallel to the direction of energy transfer. Direction of energy transfer oscillation

42. The Cathode Ray Oscilloscope Can you stick the sheet in?

43. Amplitude = volume Can you copy this CAREFULLY please?

44. Pitch = frequency Can you copy this CAREFULLY too please?

45. Range of hearing Humans can hear up to a frequency of around 20 000 Hz (20 kHz) Can you copy this too please?

46. Your own mind-map