Learning Objectives Know why light is said to travel in waves Know what polarisation is Know how diffraction patterns occur Success criteria Explain how experiments show that light travels in waves ID: 495368
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Slide1
Light WavesSlide2
Learning Objectives
Know why light is said to travel in waves.
Know what polarisation is.
Know how diffraction patterns occur.Slide3
Success criteria
Explain how experiments show that light travels in waves.
(Grade C)
Explain how polarisation occurs.
(Grade C)
Explain how diffraction patterns are formed.
(Grade A)Slide4
Starter
VideoSlide5
So light travels in straight lines...
...but it we know its path can also be bent by refraction and diffraction, just like sound and water.Slide6
Wave and particle theories of light
Particle theory:
Isaac Newton described light as particles which he called
corpuscles
.
Different colours were due to
different sized corpuscles.
His theory predicted light would travel
faster in a denser medium
.
Wave theory:
Christiaan
Huygens described light as waves which spread out in all directions.Different colours were due to different wavelengths.His theory predicted light would travel slower in a denser medium.
When the speed of light could eventually be measured, Newton was shown to be wrong.Slide7
Further evidence for the wave theory of light
RememberSlide8
When two waves from the same source meet in step (in phase)...
...
constructive
interference occurs.Slide9
When two waves from the same source meet out of step (in
antiphase
)...
...
destructive
interference occurs.Slide10
Young’s experiment (1801)
This gives a characteristic diffraction patternSlide11
Young’s experiment is evidence for the wave nature of light. Destructive interference cannot be explained by light being a particle.Slide12
Light can be Polarised
Polarized light
waves are
those which are only oscillating in
one plane
(angle)
Usually, light is unpolarised and waves
oscilliate
at
all angles
.
A
polarising filter
will
block
all but one plane of light wave.What would happen if a second polarising filter was placed in the path of the light, but at 90o to the first one.
List some used of polarising filters.Slide13Slide14
Tasks
Foundation:
Answers questions 7-10 on pages 198-199 – old course.
Higher:
Sketch figure 13 on page 199 (old course), and explain how the bands are formed.
Why is Polaroid good for use in sunglasses?Slide15
Learning Objectives
Know why light is said to travel in waves.
Know what polarisation is.
Know how diffraction patterns occur.Slide16
Success criteria
Explain how experiments show that light travels in waves.
(Grade C)
Explain how polarisation occurs.
(Grade C)
Explain how diffraction patterns are formed.
(Grade A)Slide17
Plenary
In a few sentences..
Summarise the ideas of Newton, Huygens and Young.
State why the wave theory of light is now accepted.
BE PREPARED TO READ OUT YOUR ANSWER