Topic 8 waves

Question 1

Give examples of using sound for medical diagnosis

Answer 1

• Stethoscopes = listen to sound in body
• Ultrasonograph

Question 2

Describe how an ultrasonograph works

Answer 2

• 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

Question 3

Define doppler effect

Answer 3

• Shifting of frequency when ultrasound reflects off moving target
• Basis for measuring blood flow + turbulence + speed

Question 4

How is a wave formed?

Answer 4

• Each spatial point oscillates in harmonic motion = each oscillator strict phase relationship with other points

Question 5

Define propagating wave

Answer 5

• Self-sustaining disturbance = medium travels from 1 point > another = carrying energy + momentum
• Particles of medium only oscillate in place

Question 6

Define direction of propagation

Answer 6

• The direction of energy transport
• Each particle vibrates up/down perpendicular to line of propagation

Question 7

Define transverse waves

Answer 7

• The medium in the wave is oscillating in direction perpendicular
• E.g EM waves

Question 8

Define longitudinal waves

Answer 8

• Each spatial point in medium oscillating in same direction as wave propagating
• E.g. sound waves

Question 9

Describe the structure of the wave

Answer 9

• Top point = crest
• Bottom points = trough

Question 10

Define amplitude

Answer 10

• Maximal distance = displacement from equilibrium position = during 1 complete wave cycle
• Equilibrium to trough

Question 11

Define wavelength

Answer 11

• Distance from 1 point in wave to same point on next cycle

Question 12

Define period of a wave

Answer 12

• Time taken to complete 1 full cycle
• Number of sec per cycle

Question 13

Define frequency

Answer 13

• Number of cycles per sec

Question 14

What is the formula connecting period + frequency?

Answer 14

F = 1/T
- F = HZ
- T = sec

Question 15

Define phase of wave

Answer 15

• Argunment of cos function
• Varying phase by changing point x OR changing time when observed

Question 16

What is the +/- of the phase?

Answer 16

• Negative = wave travelling in + x direction
• Positive = wave travelling in - x direction

Question 17

What happens when 2 same type of waves overlap?

Answer 17

• Superpose = new oscillation

Question 18

Define complete constructive interferance

Answer 18

• Both crests fall in phase = reinforce each other
• High intensity

Question 19

Define complete destructive interferance

Answer 19

• Cresr falls on a trough = cancel each other out
• No sound produced = 180° out of phase

Question 20

What happens when 2 different type of waves overlap?

Answer 20

• Superpose different frequencies = beats
  1) Actual frequency of resulting disturbance
  2) Frequency where max amplitude of superposition changes

Question 21

Define beat frequency

Answer 21

• Rate at which max amplitude of combined waves oscilates
• 𝒇𝑩 = 𝒇𝟏 − 𝒇2
• The smaller the difference between waves = slower beat frequency

Question 22

Define reflection

Answer 22

• 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

Question 23

Define standing wave

Answer 23

• Identical waves traveling in opposite direction

Question 24

Define power

Answer 24

• How much energy is transmitted per unit time

Question 25

Define intensity

Answer 25

• How much power per area

Question 26

What is the formula linking power + intensity?

Answer 26

I = P/A