P12 - Wave properties Flashcards
What do waves do?
transfer energy, but not matter
The matter only oscillates, but will eventually return to its original position
Name some differences between transverse and longitudinal waves:
transverse - peaks and troughs, matter oscillates perpendicular to energy transfer direction
longitudinal - compressions and rarefactions, matter oscillates parallel to energy transfer direction
The λ of a longitudinal wave is just the distance from compression to compression
What is the amplitude of a wave?
the maximum displacement of a point on a wave from its undisturbed position
State the wave equations for period, and wave velocity:
T = 1/f
v = f λ
What is wave speed?
the speed at which energy is transferred by a wave through a medium
RP8a - How can you find the speed of a wave in water?
-fill ripple tank to 5mm, and stand it over a white card, with a lamp above, then start motor to move the rod periodically
-for λ, measure between a few wavefronts and divide by the number of wavefronts
-for frequency, time how long it takes for a certain amount of wavefronts to pass a point, do #wavefronts/time
-multiply to get wave speed (v = f λ)
The water level must be 5mm otherwise it would be too high and the waves wouldn’t project well
RP8b - What is a standing wave, and what is its wavelength?
-when a wave doesn’t appear to move horizontally, and only appears to oscillate vertically
-distance between 2 loops
RP8b - How could you find the speed of a standing wave from a string?
-attach string to vibration generator, and hang over an edge across a bridge then a pulley with a mass attached for tension
-for λ, measure distance between as many stationary points as possible and divide by number of loops and multiply result by 2
-take frequency from generator
-multiply to get wave speed (v = f λ)
Remember for λ, the distance between 2 loops is one full cycle
What can happen to a wave at the boundary between 2 materials?
-transmitted
-absorbed
-reflected/refracted
How do humans hear sound?
-sound waves cause ear drum and other parts to vibrate
-causes the sensation of sound
-only works over a frequency range of 20Hz to 20kHz
Give 2 pieces of evidence that shows when a sound wave travels through the air, it is the wave and not the air itself that travels:
-a loudspeaker doesn’t cause a gust of wind
-a vibrating drum skin doesn’t move the air away to create a vacuum around the drum
What is ultrasound, and why is it useful?
-sound with a frequency higher than 20kHz
-partially reflected between the boundary of 2 media
-time taken for reflections to come back to detector can be used to find how far the change in media is
Give an example of how ultrasound is used in water:
-echo sounding
-used to detect objects in deep water and measure water depth
What are some advantages of using ultrasound over X-rays when scanning human tissue?
-can scan softer tissues which don’t absorb X-rays
-non-ionising, no damage to the body
What are seismic waves? Explain how they help us:
-waves in Earth’s crust produced by EQs
-they provide evidence for the structure and size of the Earth’s inner layers that aren’t directly observable
Why does refraction happen at the boundary between the 2 depths?
-wave velocity is slower in shallow water
-so the edge of the wavefront that is entering shallow water first slows down before the other edge
-the other edge continues at a higher speed until it also crosses the boundary, and thus changes the wave’s direction
Why don’t the water waves refract here?
-every point along each wavefront enters the shallow water at the same time
-this means every point along the wavefront slows down at the exact same time, and so no change in direction occurs
