interference interference of waves material objects cannot occupy the same place at the same time....

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 size2. the waves will decrease in size3. 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• (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 diffractionb. 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 wavesb. 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.