Interference Interference of Waves Material objects cannot occupy
Interference
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
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
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
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
b. Destructive Interference • (add) When the crest of one wave overlaps the trough of another wave, their individual effects are reduced.
• Destructive interference does not always result in waves completely cancelling: • (p 270) Constructive and destructive interference of sound waves results in beats
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.
Standing Wave • (add to margin of p 271) Standing waves are created when 2 pulses with equal and opposite amplitudes meet • Diagram:
Diffraction • (p 269) 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
Diffraction depends on the size of the opening: the smaller the opening the greater the diffraction
Diffraction depends on wavelength: the longer the wavelength the greater the diffraction
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
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.
- Slides: 18