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

Snell’s law There is a relationship between the speed of the wave in the two media and the angles of incidence and refraction θ1θ1 θ2θ2 Ray, NOT wavefronts

Snell’s law speed in substance 1 sinθ 1 speed in substance 2 sinθ 2 =

Snell’s 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 = sinθ 1 /sinθ 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

Snell’s law Thus for two different media sinθ 1 /sinθ 2 = v 1 /v 2 = n 2 /n 1

OR! Thus for two different media sinθ 1 /sinθ 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 Angle ng-lighthttp://phet.colorado.edu/en/simulation/bendi ng-light Critical angle (when angle of refraction is 90º) i

Critical angle (C) sinθ 1 /sinθ 2 = n 2 /n 1 At critical angle (C), θ 2 = 90, sinθ 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 That’s why we can hear people around a wall but not see them!

Diffraction of radio waves

Diffraction patterns

b θ 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?

Young’s original experiment Coloured filter

4.4 Young’s double-slit worksheet Mr Porter is giving you a worksheet