Topic 4 - Waves Flashcards
What are waves?
- Waves are one way in which energy may be transferred between stores.
- Both mechanical and electromagnetic waves will transfer energy but not matter.
What is frequency?
The number of waves passing a point each second.
What is the wave length?
- The distance covered by a full cycle of the wave.
- Usually measured from peak to peak, or trough to trough.
What is the rest position?
The undisturbed position of particles or fields when they are not vibrating.
What is the Displacement?
The distance that a certain point in the medium has moved from its rest position.
What is the Peak?
The number of waves passing a point each second. The highest point above the rest position.
What is the Trough?
The lowest point below the rest position.
What is the Amplitude?
The maximum displacement of a point of a wave from its rest position.
What is the time period?
- The time taken for a full cycle of the wave.
- Usually measured from peak to peak, or trough to trough
What is the difference between transverse and longitudinal waves?
- In longitudinal waves, the vibrations are parallel to the direction of wave travel.
- In transverse waves, the vibrations are at right angles to the direction of wave travel.
List examples of longitudinal. (3)
- sound waves
- ultrasound waves
- seismic P-waves
List examples of transverse waves. (5)
- ripples on the surface of water
- vibrations in a guitar string
- a Mexican wave in a sports stadium
- electromagnetic waves – eg light waves, microwaves, radio waves
- seismic S-waves
How do you work out wave speed?(2)
Wave speed (m/s) = frequency (Hz) x wavelength (m)
Or
Wave speed = distance (m) / time (s)
How do you measure the velocity of sound in air? (4)
1) Set up the oscilloscope so the detected waves each microphone are shown as separate waves.
2) Start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display, but have moved exactly one wavelength apart.
3) Measure the distance between the microphones to find one wavelength.
4) Use the formula wave speed = frequency (look on signal generator) x wavelength
How do you measure the speed of water ripples? (5)
1) Using a signal generator attached to the dipper of a ripple tank you can create water waves at a set frequency.
2) Dim the lights and turn on the strobe light - you’ll see wave pattern made by the shadows of the wave crests on the screen below the tank.
3) Alter the frequency of the strobe light until the wave pattern on the screen appears to ‘freeze’ and stop moving. This happens when the frequency of the waves and the strobe light are equal - the waves appear not to move because they are being lit at the same point in their cycle each time.
4) The distance between each shadow line is equal to one wavelength. Measure the distance between lines that are 10 wavelengths apart, then find the average wavelength
5) Use wave speed = frequency x wavelength to calculate the speed of the waves.