Waves Exam Questions Flashcards
Suggest how stationary waves are formed in a microwave oven (2)
The microwaves hit the oven wall and is reflected. The two waves moving in opposite directions interfere and produce a stationary wave
Why does chocolate only melt at certain points in a microwave (2)
It melts at the antinodes as these are the positions with highest energy and amplitude
Suggest why the amount of reflected light changes as the fibre bends (2)
The amount of reflected light increases since the angle of incidence may become less than the critical angle . The light may encounter impurities at different angles
What property of microwaves is shown by a change in current (1)
Microwaves can be polarised as they are transverse waves
How can a transmitter, a receiver and a vertical metal rod be used to demonstrate that the waves from the transmitter are vertically polarised (3)
Rotate the aerial in the vertical plane
When the aerial is vertical, the signal is at max
When the aerial is horizontal, the signal is at a minimum
What happens to the signal detected by the receiver as a vertical metal plate is moved slowly towards a point x (4)
Received signal goes through max and min
Reflected and direct microwaves interfere
Path length of reflected wave/path difference increases as the plate is moved
The max is when the aerial is aligned with the plane of polarisation of the microwave
Describe relevant procedures to limit the effect of random error in the result for the diameter of a rod (3)
Repeat readings at different points along the rod and calculate an average
Repeat readings in different directions perpendicular to the rod and calculate an average
Reject anomalous readings before taking the mean
Explain how a stationary wave is produced when a stretched string is plucked (3)
The wave travels to the boundary and the reflected wave and original wave moving in opposite directions meet and superpose.
Nodes are formed where destructive interference occurs.
Antinodes are formed when constructive interference occurs
Explain why the minimum reading on an ammeter is not zero when 2 waves combine
They did not have the same amplitude
State the conditions needed for the formation of a stationary wave
Waves must be moving in opposite directions
Waves must be of the same type with the same frequency, amplitude and equal and opposite velocities
Explain why there is a variation in loudness of sound at the microphone as the moveable tube is slowly pulled out
Initially the path difference is 0 as the waves are in phase when they meet
As the moveable tube is pulled out the path difference increases and the 2 waves are no longer in phase so displacement and loudness decrease
When the path difference is one half wavelength, the two are in antiphase and sound is at its quietest.
As the path difference continues to increase, the 2 waves become more in phase and the sound gets louder again
