Do now! Can you continue/finish the sheet we started at the end of last lesson on POLARISATION? Using ray boxes Reflection Draw around the mirror Reflection normal Reflection normal Reflection normal Reflection normal Angle of incidence Reflection normal Angle of incidence Can you quietly and sensibly follow Mr Porter? Reflection Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror Angle of incidence = Angle of reflection 4.4 Mirrors on the moon!2_RAc 4.4 Mirror Island Aim the laser at the dog! Can you arrange mirrors on the sheet to aim the laser at me? 4.4 Zap the Dog! 4.4 What colour is a mirror? Possible Homework Design your own worksheet using the law of reflection you can do something similar to Mirror Island or even better think of an even more interesting way of testing students knowledge and understanding of the law of reflection. Print your sheet out and complete it yourself. The mug trick! Why does this happen? Marching soldiers! Light waves Light slows down as it goes from air to glass/water Ripple tank Ripple Tank Simulation Snells law There is a relationship between the speed of the wave in the two media and the angles of incidence and refraction 11 22 Ray, NOT wavefronts Snells law speed in substance 1 sin 1 speed in substance 2 sin 2 = Snells law In the case of light only, we usually define a quantity called the index of refraction for a given medium as n m = c = sin 1 /sin 2 c m where c is the speed of light in a vacuum and c m is the speed of light in the medium vacuum c cmcm Snells law Thus for two different media sin 1 /sin 2 = v 1 /v 2 = n 2 /n 1 OR! Thus for two different media sin 1 /sin 2 = v 1 /v 2 = n 2 /n 1 = 1 n 2 Refraction a few notes The wavelength changes, the speed changes, but the frequency stays the same Refraction a few notes When the wave enters at 90, no change of direction takes place. 4.4 Refraction worksheet i 4.4 Measuring refractive index r Critical angle i i i Critical Angleng-lighthttp://phet.colorado.edu/en/simulation/bendi ng-light Critical angle (when angle of refraction is 90) i Critical angle (C) sin 1 /sin 2 = n 2 /n 1 At critical angle (C), 2 = 90, sin 2 = 1 sinC = n 2 /n 1 = 1/n 1 if into air/vacuum Right-angled prisms Right-angled prism? ? Right-angled prisms Bigger than Critical angle Examples of Total Internal Reflection 4.4 Critical angle worksheet Diffraction Waves spread as they pass an obstacle or through an opening Diffraction Diffraction is most when the opening or obstacle is similar in size to the wavelength of the wave Diffraction Diffraction is most when the opening or obstacle is similar in size to the wavelength of the wave Diffraction Ripple Tank Simulation Diffraction Thats why we can hear people around a wall but not see them! Diffraction of radio waves Diffraction patterns b n = 1 n = 2 4.4 Diffraction worksheet Superposition Principle of superposition When two or more waves meet, the resultant displacement is the sum of the individual displacements Constructive and destructive interference When two waves of the same frequency superimpose, we can get constructive interference or destructive interference. + = + = Superposition In general, the displacements of two (or more) waves can be added to produce a resultant wave. (Note, displacements can be negative) Interference patterns Ripple Tank Simulation If we pass a wave through a pair of slits, an interference pattern is produced Can you follow Mr Porter? Path difference Whether there is constructive or destructive interference observed at a particular point depends on the path difference of the two waves Constructive interference if path difference is a whole number of wavelengths antinode Destructive interference if path difference is a half number of wavelengths node Destructive interference if path difference is a half number of wavelengths 4.4 Interference questions Double slit interference s s s s With white (non-monochromatic) light? Youngs original experiment Coloured filter 4.4 Youngs double-slit worksheet Mr Porter is giving you a worksheet