1. Light Waves

2. Learning Objectives Know why light is said to travel in waves.
Know what polarisation is.
Know how diffraction patterns occur.

3. 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)

4. Starter
Video

5. 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.

6. 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.

7. Further evidence for the wave theory of light Remember

8.  When two waves from the same source meet in step (in phase)...
...constructive interference occurs.

9. When two waves from the same source meet out of step (in antiphase)...
...destructive interference occurs.

10. This gives a characteristic diffraction pattern
Young’s experiment (1801)
This gives a characteristic diffraction pattern

11. Young’s experiment is evidence for the wave nature of light
Young’s experiment is evidence for the wave nature of light. Destructive interference cannot be explained by light being a particle.

12. 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.

14. Tasks
Foundation:
Answers questions 7-10 on pages – 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?

15. Learning Objectives Know why light is said to travel in waves.
Know what polarisation is.
Know how diffraction patterns occur.

16. 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)

17. Plenary In a few sentences.. BE PREPARED TO READ OUT YOUR ANSWER
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