2. Interference

3. Interference of Waves Material objects cannot occupy the same place at the same time. for example 2 rocks cannot be at the same spot at the same time But waves can exist at the same time in the same space Take those 2 rocks and drop them in water, the waves can overlap and form in interference pattern

4. Interference Patterns As these waves interfere with each other, one of three things will happen: 1.the waves will increase in size 2.the waves will decrease in size 3.the waves will cancel

5. Superposition Principal (p 269) The superposition principal states that when there are 2 sources of waves in a medium, these waves will combine to give a resultant wave that is the algebraic sum of all the waves (add) this can only happen with waves, not particles The superposition principal explains constructive and destructive interference

6. a. Constructive Interference (add) When the crest of one wave overlaps the crest of another, their individual effects add together. (add) Once the waves have passed through each other they continue in their original directions

7. b. Destructive Interference (add) When the crest of one wave overlaps the trough of another wave, their individual effects are reduced.

8. Destructive interference does not always result in waves completely cancelling: (p 270) Constructive and destructive interference of sound waves results in beats

10. Reflection of Waves If you tied a piece of rope to a wall and shook the free end up and down, you would produce a wave in the rope. Since the wall is too rigid to shake, the wave is reflected back along the rope. by shaking rope at the proper frequency you can cause the incident (original) and reflected waves to form a standing wave.

11. Standing Wave (add to margin of p 271) Standing waves are created when 2 pulses with equal and opposite amplitudes meet Diagram:

15. Diffraction (p269) Only waves diffract (particles do not) Diffraction is the spreading out of a wave as it passes through a small opening or around an obstacle The amount of diffraction depends on: a. the size of the opening: the smaller the opening the greater the diffraction b. the wavelength: the longer the wavelength the greater the diffraction Huygen’s explained diffraction in his principle

16. Diffraction depends on the size of the opening: the smaller the opening the greater the diffraction

17. Diffraction depends on wavelength: the longer the wavelength the greater the diffraction

18. Review A wave is a wiggle is space and time Waves carry energy without transferring matter Wavelength is the distance between two identical parts of the wave (crest-crest or trough-trough) Waves can be classified based on how they travel: a. In a vacuum: electromagnetic waves b. Needs a medium: mechanical waves

19. Review continued There are two main types of mechanical waves: i) Transverse ii) Longitudinal In constructive interference, crests overlap In destructive interference, a crest overlaps a trough In a standing wave, points of complete destructive interference (nodes) remain stationary.