1. 11/11/2015Waves W Richards The Weald School

2. 11/11/2015 Simple Harmonic Motion Definition: simple harmonic motion is when acceleration is proportional to displacement and is always directed towards equilibrium.

3. 11/11/2015 Simple Harmonic Motion Consider a pendulum bob: Let ’ s draw a graph of displacement against time: Displacement Time Equilibrium position “ Sinusoidal ”

4. 11/11/2015 SHM Graphs Time Displacement Velocity Acceleration Time

5. 11/11/2015 Waves revision Watch a “ Mexican Wave ”

6. 11/11/2015 Some definitions… 1) Amplitude – this is “ how high ” the wave is: 2) Wavelength ( ) – this is the distance between two corresponding points on the wave and is measured in metres: 3) Frequency – this is how many waves pass by every second and is measured in Hertz (Hz)

7. 11/11/2015 Transverse vs. longitudinal waves Transverse waves are when the displacement is at right angles to the direction of the wave… Longitudinal waves are when the displacement is parallel to the direction of the wave… Displacement Direction Displacement

8. 11/11/2015 The Wave Equation The wave equation relates the speed of the wave to its frequency and wavelength: Wave speed (v) = frequency (f) x wavelength ( ) in m/s in Hz in m V f

9. 11/11/2015 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

10. 11/11/2015 Refraction Revision

11. 11/11/2015 Refraction through a glass block: Wave slows down and bends towards the normal due to entering a more dense medium Wave speeds up and bends away from the normal due to entering a less dense medium Wave slows down but is not bent, due to entering along the normal

12. 11/11/2015 Finding the Critical Angle… 1) Ray gets refracted 4) Ray gets internally reflected 3) Ray still gets refracted (just!) 2) Ray still gets refracted THE CRITICAL ANGLE

13. 11/11/2015 Uses of Total Internal Reflection Optical fibres: An optical fibre is a long, thin, _______ rod made of glass or plastic. Light is _______ reflected from one end to the other, making it possible to send ____ chunks of information Optical fibres can be used for _________ by sending electrical signals through the cable. The main advantage of this is a reduced ______ loss. Words – communications, internally, large, transparent, signal

14. 11/11/2015 Wave diagrams 1) Reflection 4) Diffraction3) Refraction 2) Refraction

15. 11/11/2015Diffraction More diffraction if the size of the gap is similar to the wavelength More diffraction if wavelength is increased (or frequency decreased)

16. 11/11/2015 Sound can also be diffracted… The explosion can ’ t be seen over the hill, but it can be heard. We know sound travels as waves because sound can be refracted, reflected (echo) and diffracted.

17. 11/11/2015 Diffraction depends on frequency… A high frequency (short wavelength) wave doesn ’ t get diffracted much – the house won ’ t be able to receive it…

18. 11/11/2015 Diffraction depends on frequency… A low frequency (long wavelength) wave will get diffracted more, so the house can receive it…

19. 11/11/2015 Phase Difference Phase difference means when waves have the same frequency but oscillate differently to each other. For example: These two waves have different amplitudes but the same frequency and hit their peaks at the same time – they are “ in phase ” These two waves start opposite to each other – they are “ in antiphase ” or “ out of phase by π radians ”

20. 11/11/2015 Phase Difference What is the phase difference between each of these waves?