Waves Flashcards
Define a period.
The time it takes for a wave to complete one cycle.
What may happen to the a) wave speed b) frequency and c) wavelength of a wave when the wave travels from one medium to another.
a) changes
b) always stays the same
b) changes
What moves when someone is speaking?
The voice box vibrates, producing sound waves that travel through the air.
The air does not move.
What moves when a stone is dropped into water?
Ripples are produced.
The water and the stone do not move.
On a longitudinal wave, what are compressions and rarefactions.
Compressions = areas of high pressure
Rarefactions = areas of low pressure
Define a mechanical wave.
An oscillation that has to travel through matter (medium) transferring energy from one point to another e.g. sound waves.
How may you investigate the properties of waves?
- Have two people stand 100m apart, measured using a trundle wheel.
- Have one person make a loud noise e.g. by banging together two cymbals.
- The other person starts a stopwatch when they see the other person make the noise and stop it when they hear it.
- Repeat the experiment two more times and calculate the mean.
- Use v = s / t to calculate the speed of sound in air.
How do you measure the velocity of ripples on a water surface?
- Set up a ripple tank with water to a depth of 5 cm.
- Shine a lamp on the ripple tank and get the bobber to dip in and out of the water/adjust the height of a wooden rod to just touch the water surface and turn the motor on so that low frequency waves are observed.
- Wait until the first ripple reaches the end of the tank and take a photo.
- Use a metre ruler to measure the total length of five waves and divide by the number of ripples (five) to calculate the mean wavelength.
- Count the numer of ripples that pass a point in 10 seconds (measured with a stop watch). Divide this by 10 to calculate the mean frequency.
- Calculate the wave speed using v = f λ
Define wave absorption.
The energy of the wave is transferred into energy stores within the material it travels into.
Define wave transmission.
The waves continue to move into the substance after crossing the boundary between two materials.
What causes the sensation of sound?
Sound waves cause the ear drum and then other parts of the ear (three small bones) to vibrate. These vibrations are transmitted to the cochlea, where they produce electrical signals. These are passed to the brain, which interprets them as sound.
What restricts the limits of human hearing?
The conversion of sound waves to vibrations of solids only works over a limited frequency range.
Give three uses of ultrasound.
- Imaging of foetuses
- Cleaning jewellery
- Breaking down kidney stones
When an ultrasound wave meets a boundary between two materials, it is ____.
partially reflected
How can ultrasound be used to form a medical image?
Ultraound is emitted and sent through the skin. They travel through the body and are reflected by different boundaries between tissues.
The time taken for the reflections to reach a detector can be used to determine how far away a boundary is using s = v t.
The distance is halved to find the depth.
Define sonar.
A technique using ultrasound to detect underwater objects, their distances and their directions.
How are wave fronts affected if a wave slows down when crossing a boundary?
The wave fronts become closer together.
How are wave fronts affected if a wave crosses a boundary at an angle?
One end of the wave front changes speed before the other, making the wave refract (change direction).
How can radio wabes be produced?
They can be produced by oscillations in electrical
circuits.
What happens when radio waves are absorbed by an object?
They may create an alternating current with the same frequency as the radio wave itself, so radio waves can induce oscillations in an electrical circuit.
Is energy level 2 closer or further away from the nucleus than energy level 4?
Closer to.
