4.3- WAVE PROPERTIES 1 Flashcards
Examples of wave properties? (3)
reflection
refraction
diffraction
What can be used to study wave properties?
ripple tank
What is a ripple tank?
shallow transparent tray of water with slopping sides
What do the slopes of a ripple tank do?
prevent waves reflecting off sides of tank
What would happen if the waves did reflect in a ripple tank?
would be difficult to see waves
What are waves observed in a ripple tank called?
wavefronts
What are wavefronts?
lines of constant phase (e.g. crests)
What is the direction in which a wave travels like in comparison to the wavefront?
direction in which a wave travels is at right angles to wavefront
What do waves directed at a certain angle to a hard flat surface (reflector) do? (hint- reflect)
reflect off at same angle
angle between reflected wavefront + surface is same as angle between incident wavefront + surface
What can be said about the direction of the reflected wave as the angle between the reflected wavefront + surface is the same as the angle between the incident wavefront + surface? (reflection)
direction of reflected wave at same angle to reflector as direction of incident wave
When is the effect of reflection observed?
when light ray directed at plane mirror
What is the angle between the incident ray and the mirror like when a light ray is directed at a plane mirror? (reflection)
equal to angle between reflected ray + mirror
What changes when waves pass across a boundary? (2)
wave speed changes
wavelength changes
What happens if a wavefront approaches a boundary at an angle? (reflection)
change direction as well as changing speed- refraction
Why does refraction happen when water waves in a ripple tank pass across a boundary from deep to shallow water at an angle to the boundary?
they move more slowly in shallow water, wavelength is smaller in shallow water so change direction
When is refraction of light observed?
when light ray directed into glass block at an angle
What happens when light ray is directed into a glass block at an angle?
light ray changes direction when it crosses glass boundary
Why does the light ray change direction when it crosses the glass boundary? (refraction)
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
When can the effect of diffraction be seen?
in ripple tank when straight waves directed at gap
What happens when diffraction is being observed in a ripple tank (straight waves directed at gap) and the gap is now narrower?
narrower the gap, the more the waves spreads out
What happens when diffraction is being observed in a ripple tank (straight waves directed at a gap) and the wavelength is now longer?
longer the wavelength, the more the waves spread out
To consider why waves are diffracted on passing through the gap, what should each point on a wavefront be considered as?
as a secondary emitter of wavelets
How do the wavelets from the points along a wavefront travel? (diffraction)
only in direction in which wave travelling, not in reverse direction, + combine to form new wavefront spreading beyond gap
Where do satellite TV dishes in Europe need to point?
south
Why do satellite TV dishes in Europe need to point south?
as satellites orbit Earth directly above the equator
What happens the bigger the satellite TV dish?
the stronger the signal it can receive
Why can bigger satellite TV dishes receive stronger signals?
as more radio waves are reflected by the dish onto the aerial
What is a disadvantage of a bigger satellite TV dish?
reflects radio waves to smaller focus, as it diffracts waves less
What happens as bigger satellite TV dishes reflect radio waves to a smaller focus?
dish needs to be aligned more carefully than smaller dish, otherwise it will not focus radio waves on aerial
