4.3 Wave properties 1 Flashcards
What can be used to study wave properties
A ripple tank
What is a ripple tank
A shallow transparent tray of water with sloping sides. The slopes prevent waves reflecting off the sides of the tank. The direction in which a wave travels is perpendicular to the wavefront
What are the waves observed in a ripple tank referred to as
Wavefronts
Which are lines of constant phase (eg. crests)
Observing reflection
When a light ray is directed at a plane mirror
Straight waves directed at a certain angle to a hard flat surface reflect off at the same angle
The angle between the reflected wavefront and the surface is the same as the angle between the incident wavefront and the surface.
What happens when waves pass across a boundary at which the wave speed changes
The wavelength also changes
If the wavefronts approach at an angle to the boundary…
…they change direction as well as changing speed
Where does refraction happen in a ripple tank
When waves pass across a boundary from deep to shallow water at an angle to the boundary
What is the refraction in a ripple tank
The waves move more slowly in the shallow water, the wavelength is smaller in shallow water and so they change direction when going from the deeper water to shallower
When is refraction of light observed
When a light ray is directed into a glass block at an angle
The light ray changes direction when it crosses the glass boundary. This happens because light waves travel more slowly in glass than in air
Diffraction occurs when…
…waves spread out after passing through a gap or round an obstacle
Diffraction - the narrower the gap, the…
…more the waves spread out
Diffraction - the longer the wavelength, the…
…more the waves spread out
Why are the waves diffracted on passing through the gap
Each point on a wavefront can be considered to be an emitter of wavelets. The wavelets from the points along a wavefront travel only in the direction in which the wave is travelling, not in the reverse direction, and they combine to form a new wavefront spreading beyond the gap.
Why do satellite TV dishes in Europe need to point south?
Because the satellites orbit the Earth directly above the equator
Why are bigger satellite TV dishes able to receive stronger signals
Because more radio waves are reflected by the dish onto the aerial. But a bigger dish reflects the radio waves to a smaller focus, because it diffracts the waves less. The dish therefore needs to be aligned more carefully than a smaller dish otherwise the radio waves will not focus onto the aerial
