Topic 4 - Waves Flashcards
Waves basics
What do waves do?
Waves transfer energy from one place to another without transferring any matter.
Waves basics
What happens when a wave travels through a medium?
The particles of the medium vibrate and transfer energy between each other e.g. if you drop a twig in a stagnant pool the ripples don’t carry the twig away as the water only moves up and down.
Waves basics
Define amplitude
Maximum displacement from rest position of a wave that measures the amount of energy the wave transfers
Waves basics
Define trough
The lowest point of the wave
Waves basics
Define crest
The highest point of the wave
Waves basics
What is the rest position of a wave
The point of zero displacement on a wave (undisturbed)
Waves basics
What is the wavelength of a wave
The distance from trough to trough or crest to crest measured in metres
Waves basics
Define frequency
Number of oscillations a wave completes every second (Hz). 1 Hz is 1 wave per second
Waves basics
Define period
The time it takes for one oscillation to occur. (seconds)
Period = 1 / frequency
Waves basics
Define wave speed
Wave speed (m/s) = distance (m) / time (seconds)
How far the wave travels every second
Transverse and longitudinal
What is a transverse wave?
Give examples
A wave where the oscillations are perpendicular to the direction the wave travels/perpendicular to the direction of energy transfer.
Examples in include:
* All electromagnetic waves
* S-waves
* Water waves
Transverse and longitudinal
What is a longitudinal wave?
Give examples
A wave where the oscillations are parallel to the direction the wave travels
Examples include:
* Sound waves
* P-waves
Measuring wave speed
How do you measure the speed of sound using on oscilloscope?
- Set up the oscilloscope so the detected waves at each microphone are shown as separate waves.
- Start with both microphones next to the speaker then move one away until the 2 waves are alinged again but 1 wavelength apart.
- Measure distance between 2 microphones which = wavelength.
- Use formula velocity = frequency * wavelength (the frequency = frequency set in the signal generator)
Measuring speed of water waves
How do you measure the speed of water ripples?
- Using a signal generator attached to the dipper of a ripple tank you can create water waves at a set frequency.
- Dim the lights in the room and turn on a strobe light above the ripple tank which will create a wave pattern shadow below.
- Alter the frequency of the strobe light so the shadows appear to be still
- Distance between 2 shadows = wavelength (λ)
- Measure to find average
- Use velocity (m/s) = frequency (Hz) * wavelength (λ) to calculate the speed
Waves at boundaries
What are the 3 possible outcomes when a wave reaches a boundary between 2 materials?
- Absorbed - The wave transfers energy into the material’s energy stores (often thermal)
- Transmitted - The wave carries on travelling through the material (leads to refraction)
- Reflection - The wave is ‘sent back’