Topic 8 waves Flashcards
Give examples of using sound for medical diagnosis
- Stethoscopes = listen to sound in body
- Ultrasonograph
Describe how an ultrasonograph works
- Non- destructive imaging method
- Uses sound = frequency above hearing = image
- Waves sent to object = reflected
- Delay time between transmission of beam + arrival of reflected pulse at detector = relative location of object
Define doppler effect
- Shifting of frequency when ultrasound reflects off moving target
- Basis for measuring blood flow + turbulence + speed
How is a wave formed?
- Each spatial point oscillates in harmonic motion = each oscillator strict phase relationship with other points
Define propagating wave
- Self-sustaining disturbance = medium travels from 1 point > another = carrying energy + momentum
- Particles of medium only oscillate in place
Define direction of propagation
- The direction of energy transport
- Each particle vibrates up/down perpendicular to line of propagation
Define transverse waves
- The medium in the wave is oscillating in direction perpendicular
- E.g EM waves
Define longitudinal waves
- Each spatial point in medium oscillating in same direction as wave propagating
- E.g. sound waves
Describe the structure of the wave
- Top point = crest
- Bottom points = trough
Define amplitude
- Maximal distance = displacement from equilibrium position = during 1 complete wave cycle
- Equilibrium to trough
Define wavelength
- Distance from 1 point in wave to same point on next cycle
Define period of a wave
- Time taken to complete 1 full cycle
- Number of sec per cycle
Define frequency
- Number of cycles per sec
What is the formula connecting period + frequency?
F = 1/T
- F = HZ
- T = sec
Define phase of wave
- Argunment of cos function
- Varying phase by changing point x OR changing time when observed
What is the +/- of the phase?
- Negative = wave travelling in + x direction
- Positive = wave travelling in - x direction
What happens when 2 same type of waves overlap?
- Superpose = new oscillation
Define complete constructive interferance
- Both crests fall in phase = reinforce each other
- High intensity
Define complete destructive interferance
- Cresr falls on a trough = cancel each other out
- No sound produced = 180° out of phase
What happens when 2 different type of waves overlap?
- Superpose different frequencies = beats
1) Actual frequency of resulting disturbance
2) Frequency where max amplitude of superposition changes
Define beat frequency
- Rate at which max amplitude of combined waves oscilates
- 𝒇𝑩 = 𝒇𝟏 − 𝒇2
- The smaller the difference between waves = slower beat frequency
Define reflection
- Waves hit a barrier = wave reflected back
1) Attachment point fixed = inverted = upside down - Equal in magnitude + opposite direction
2) Attachment point not fixed = reflected back in same orientation - Incoming + reflected will superpose = 2x amplitude
Define standing wave
- Identical waves traveling in opposite direction
Define power
- How much energy is transmitted per unit time
Define intensity
- How much power per area
What is the formula linking power + intensity?
I = P/A
