*WavesW RichardsThe Weald School

*Simple Harmonic MotionDefinition: simple harmonic motion is when acceleration is proportional to displacement and is always directed towards equilibrium.

*Simple Harmonic MotionConsider a pendulum bob:Lets draw a graph of displacement against time:

*SHM GraphsTimeDisplacementVelocityAccelerationTimeTime

*Waves revisionWatch a Mexican Wave

*Some definitions1) 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)

*Transverse vs. longitudinal wavesTransverse waves are when the displacement is at right angles to the direction of the waveLongitudinal waves are when the displacement is parallel to the direction of the wave

*The Wave EquationThe 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

*A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is it moving?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?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?Purple light has a wavelength of around 6x10-7m and a frequency of 5x1014Hz. What is the speed of purple light?Some example wave equation questions0.2m0.5m0.6m/s3x108m/s

*Refraction Revision

*Refraction through a glass block:Wave slows down but is not bent, due to entering along the normal

*Finding the Critical Angle1) Ray gets refracted4) Ray gets internally reflected3) Ray still gets refracted (just!)2) Ray still gets refracted

*Uses of Total Internal ReflectionOptical 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 informationOptical 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

*Wave diagrams1) Reflection4) Diffraction3) Refraction2) Refraction

*DiffractionMore diffraction if the size of the gap is similar to the wavelengthMore diffraction if wavelength is increased (or frequency decreased)

*Sound can also be diffractedThe explosion cant 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.

*Diffraction depends on frequencyA high frequency (short wavelength) wave doesnt get diffracted much the house wont be able to receive it

*Diffraction depends on frequencyA low frequency (long wavelength) wave will get diffracted more, so the house can receive it

*Phase DifferencePhase 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 phaseThese two waves start opposite to each other they are in antiphase or out of phase by radians

*Phase DifferenceWhat is the phase difference between each of these waves?