Waves Flashcards
Describe transverse waves.
- the oscillations are perpendicular to the direction of the energy transfer (at right angles)
- the oscillations go up and down
- but direction of energy transfer is sideways
Longitudinal waves
Oscillations are parallel to the direction of energy transfer.
Require a medium to travel in.
Define frequency?
Number of waves that pass a certain point per second.
Describe how sound waves work in a microphone.
- when sound waves hit the paper cone, this causes it to vibrate
- microphone converts this into electrical signals.
Describe how sound waves work in the ear.
- sound waves in the air are funneled into the ear where they hit the eardrum
- ear drum is a thin membrane
- sound waves cause the eardrum and other parts of the inner ear to vibrate
- causes the sensation of sound.
State the normal human frequency range of hearing.
20-20000Hz
-frequencies outside this range may not be able to make the ear drum vibrate
Why do sound waves travel so much faster in solids?
- the particles are much closer together
- the vibrations can pass more easily between them
Why does frequency not change when a wave changes medium?
- this is because the waves would have to be destroyed or created at the boundary
- which isn’t possible
What is the problem with cathode ray oscilloscopes?
- represent sound waves as if they were transverse waves
- but sound waves are longitudinal
What is a reflected sound wave?
An echo.
Why can sound waves only travel through mediums?
- sound waves only move by particles vibrating
- sound waves cannot pass through a vacuum as there are no particles
What is ultrasound?
Sound waves with a frequency higher than the upper limit of human hearing, so it is at least 20,000Hz
Does ultrasound scanning work for any organ surrouned by bone?
No
What is the speed of ultrasound in water?
1600m/s
When can refraction happen?
When any wave changes speed as it passes from one medium to another.
Rays of light entering a glass block.
- when light passes from the air into the glass, the velocity of light decreases
- this causes the direction of the waves to change
- when waves slow down, they bend towards the normal
- light waves now pass through the glass block
- when waves pass from the glass into the air, their velocity increases
- when waves speed up, they bend away from the normal
- causes the image of the object to appear to have shifted position
When do waves NOT change direction when entering/leaving a medium?
If the waves enter or leave the medium at right angles to the surface (along the normal).
Describe ultrasound pulses reflecting off of a kidney
- if we know the time it takes for the ultrasound pulse to leave the probe and bounce off the kidney, and then be collected by the probe
- we can calculate the distance between the porbe and the kidney
Why is ultrasound safer than x-rays?
-doesn’t cause any mutations or increase the risk of cancer
Why are wavefronts used?
Make it easier to visualise lots of waves moving together
Why do earthquakes happen?
- due to a sudden movement between the tectonic plates in the earth’s crust
- these cause seismic waves which carry energy away from the earthquake
Describe p-waves
- longitudinal
- can pass through both solids and liquids
- travel faster than s-waves
Describe s-waves
- transverse waves
- s-waves can only travel through solids
Why do seismic waves travel in curved paths?
-due to density changes in the earth
How do scientists know about the liquid outer core?
- s waves cannot pass through a liquid
Why are there p-wave shadow zones?
- p waves travel faster in solids than in liquids
- they slow down as they enter the liquid outer core
- which causes them to refract as they leave or enter
How did scientists know about the solid inner core?
-faint p-waves can be detected on the p-wave shadow zone.
