1. Waves Superposition and Standing Waves The Electromagnetic Spectrum Pulse-Echo Techniques Refraction Polarisation Diffraction

2. Understand the terms Amplitude and Wavelength Amplitude: the maximum displacement of a particle from the midpoint of the oscillation. Decreases with distance Wavelength: the distance between 2 consecutive points. Ie: from crest-crest or trough-trough

3. Understand the term Frequency The number of oscillations per second (Hertz)

4. Understand the term Period The time taken for one complete oscillation / wave / vibration to occur. T = 1/f

5. Wave Speed Use the wave equation below Wave speed: the distance travelled by the wave each second (m/s)

6. Identify different regions of EM spectrum and describe some of their applications.

7. Oscillation An oscillation is a regular to-and-fro motion A travelling wave transfers energy by means of oscillations

8. Longitudinal Waves Particles oscillate back and forth along the line in which the wave progresses. Eg: Sound Waves

9. Transverse Wave Particles oscillate at right angles to the direction of propagation of the wave. Eg: Light Waves

10. Displacement-Distance Graphs Shows the position of all the particles at a single instant along a section of the wave. Shows the wavelength of the wave.

11. Displacement-Time Graphs Describes the movement of a single particle within a wave. Shows the time period of the wave.

12. Representing a Longitudinal Wave on a Graph

13. Cycles of a Vibration A complete cycle of a vibration is equivalent to an angle of 360o or 2π radians

14. Phase Difference In Phase: Two points on a wave are in phase if they are both at the same point in the wave cycle. Out of Phase: Two points on a wave are out of phase if they are not on the same point in the wave cycle.

15. Antiphase The amount by which such oscillators are out of step with each other can be expressed in degrees from 0° to 360°, or in radians from 0 to 2π. If the phase difference is 180 degrees (π radians), then the two oscillators are said to be in antiphase causing destructive interference.

16. Wavefront A line joining points in a wave that are in phase with each other. EG: a line joining the crest particles together.

17. Superposition When two waves of the same type (eg: two water waves) arrive at the same point, their displacements will combine to result in a wave of different amplitude Waves do not need to have the same frequency or wavelength

18. Coherence Wave sources are said to be coherent if: 1.The waves are of the same type (eg: light waves) 2.The waves have the same frequency and wavelength 3.The waves have a constant phase difference Interference patterns can only be caused by coherent waves Coherent Incoherent

19. Interference Interference is a specific type of superposition Interference patterns can only be caused by coherent waves and waves of the similar amplitudes

20. Path Difference When one wave has travelled further than another. The difference between the distances from two sources to a given point.

21. Constructive Interference When path difference is a whole number of wavelengths. Eg: 1, 2, 3, etc

22. Destructive Interference When the path difference is ½ or 1½ or 2½, etc

23. Waves reflected off a boundary If a wave travelling along a string is reflected at a fixed end, there is a phase change of 180o (pi radians).

24. Standing (Stationary) Waves If a wave is repeatedly reflected this can produce a standing wave. Caused by the superposition of two waves of the same wavelength, travelling in opposite directions.

25. Standing Waves in a String The lowest frequency is the fundamental frequency 5 th Harmonic 4 th Harmonic 3 rd Harmonic 2 nd Harmonic 1 st Harmonic (Fundamental Frequency)

26. Standing Waves in Closed and Open Tube Closed = node Open = antinode

27. Refractive Index Snell’s Law 1 u 2 = sin incident angle / sin refracted angle 1 u 2 = incident speed / refracted speed Speed decreases Wavelength decreases Frequency unchanged

28. Critical Angle / Total Internal Reflection 1 u 2 = sin n 1 angle / sin n 2 angle sin n 1 = sin 90 = 1 Therefore: 1 u 2 = 1 / sin n 2 angle Predict whether total internal reflection will occur at an interface

29. Optical Fibres Light running through optical fibres is used to transmit phone and cable tv signals. This is better than electricity through a wire because: 1.Light can carry more information 2.Light doesn’t heat up the fibre 3.There is no electrical interference

30. Light Waves Varying Electric and Magnetic fields. Oscillations/vibrations are in all planes at right angles to the direction of travel.

31. Plane Polarised Light When light is passed through a polarising filter, the oscillations in all directions but one will be absorbed. The light emerging from the sheet has its electric/magnetic vector oscillating in one direction and is said to be plane polarised. This is one proof that light is a transverse wave.

32. Optical Activity Explain how to measure the rotation of the plane of polarisation: 1.Optical active substances such as sugar rotate the plane of polarisation. This rotation is proportional to their concentration and the depth of liquid. This can be used to measure the concentration of sugar solutions. 2.Suppose a second filter is held beyond the first filter. As this filter is rotated, alternating maximum and minimum light intensities will be observed every 90 o. If light has been polarised due to a material, this angle will be less/more.

33. Light will get polarised when it: –Reflects off certain materials –Travels through certain materials

34. Diffraction The spreading out of waves as they pass through openings, or the edges of obstacles. Substantial diffraction occurs when the size of the gap or obstacle is similar in wavelength of the wave

35. Evidence for the Wave Nature of Electrons Electrons produced diffraction patterns in experiments. They didn’t produce results you would expect particles to.

36. Discuss how scientific ideas change over time. EG: our ideas on the particle/wave nature of electrons Past → Present

37. Waves are Transmitted and Reflected at an interface between media Boundary between two media is called an interface If the media is very different most of the energy is reflected. If media are quite similar most of the energy is transmitted.

38. Doppler Effect For all waves, movement of the source produces change in the frequency and wavelength that the observer detects. Speed of the wave does not change Sound: high frequency = high pitch (baby cry)

39. Pulse-Echo Technique Distance: Measure the time taken for a pulse to travel a distance to an object and back again. (Speed=Distance/Time) Speed (eg: of bloodstream, fish): Ultrasound beam is reflected from particles in the bloodstream back to the transducer. By measuring the change in frequency of the reflected beam, the rate of flow can be calculated. (Doppler Effect). Velocity=frequency x wavelength

40. Red Shift ● Sources of light moving away from you will shift towards the red part of the spectrum as this indicates an increase in wavelength. ● Big Bang: The further a galaxy is away from Earth, the bigger it’s redshift.

41. Ultrasound If reflected waves reach the transducer while it is transmitting, the information will be lost and image quality reduced. This means: 1.The pulses of ultrasound transmitted must be very short so that reflections don’t return before the pulse has ended. 2.The gap between pulses must be long so that the reflected waves return before the next pulse is transmitted. High frequency/small wavelength sound waves are used to prevent unwanted diffraction effects

42. Diffraction Gratings The more slits you have, the sharper the image The bigger the gap between the slits, the less that pattern will spread out.