Chapter 4.3-4.4 wave properties

wavefronts

lines of constant phase - waves observed in a ripple tank

the direction that waves travel in a ripple tank

at right angles to the wavefront

what is the angles between the reflected wavefront and the surface the same as

the angle between the incident wavefront and the surface - so the direction of the reflected wave is at the same angle to the reflectors as the direction of the incident wave

what is observed when a light ray is directed at a plane mirror, in terms of the angles seen

the angle between the incident ray and the mirror is equal to the angle between the reflected ray and mirror

what happens if wavefronts approach at an angle to a boundary

they change direction as well as changing speed = refraction

what happens when waves pass across a boundary at which the wave speed changes

the wavelength changes

why is the wavelength of water waves smaller in shallow water

they move more slowly in shallow water, and so also change direction

when is refraction of light observed

when a light ray is directed into a glass block at an angle

why does a light ray change direction when it crosses the boundary into a glass block

because light waves travel more slowly in glass than in air

when does diffraction occur

when waves spread out after passing through a gap or round an obstacle

how does the gap that a waves pass through effect diffraction

the narrower the gap, the more the waves spread out

how does the wavelength effect diffraction

the longer the wavelength, the more the waves spread out

how does the size of a satellite dish affect the signal it can receieve

the bigger the dish, the stronger the signal it can receive, because more radio waves are reflected by the dish onto the aerial

why would a larger satellite dish need to be aligned more carefully than a smaller dish

a bigger dish reflects the radio waves to a smaller focus, because it diffracts the waves less - so if its not aligned carefully, it won't focus the radio waves onto the aerial

the principle of superposition

when 2 waves meet, the total displacement at a point is equal to the sum of the individual displacements at that point

supercrest

where a crest meets a crest, and the 2 waves reinforce each other

super trough

where a trough meets a trough, and the 2 waves reinforce each other

what happens when a crest meets a trough of the same amplitude

the resultant displacement is zero, as the 2 waves cancel each other out

what happens when a crest meets a trough of a different amplitude

the resultant is a minimum

node

point of no displacement - at each node, the 2 sets of waves are always 180 degrees out of phase, so the cancel each other out

when are points of cancellation created in a ripple tank

where a crest from one wave meets a trough from the other wave - the points of cancellation are seen as gaps in the wavefront

when are points of reinforcement created in a ripple tank

where a crest from one wave meets a crest from the other wave, or where a trough from one wave meets a trough from the other

interference

cancellation and reinforcement occurs at fixed positions because the waves are continuously passing through each other at constant frequency and at constant phase difference

what pattern of waves do coherent wave sources produce

produce an interference patter when the waves overlap, because they vibrate at the same frequency with a constant phase difference

how to show that microwaves become weaker as they travel away from a transmitter

place a receiver in the path of a microwave beam from a transmitter, and move the receiver gradually away from the transmitter - the receiver signal decreases with distance from the transmitter

how to show that microwaves cannot pass through metal

place a metal plate between a transmitter and a receiver

how does the width of a slit effect diffraction

the wider the slit, the less diffraction that occurs