Unit4 AOS1 - Properties of Mechanical Waves

Question 1

What is a Mechanical Wave

Answer 1

transfer of energy without the net transfer of matter, through a medium

Energy is propagated through the wave, however, the air particles (or whatever medium) doesn’t travel with the wave, rather, the particles oscillate around their respective positions

Question 2

Transverse Waves (name of positions, reference used for the y axis, examples)

Answer 2

Oscillations are perpendicular to direction of travel (up/down)

Crests - Maximum Positive Displacement
Troughs - Maximum Negative Displacement

Displacement is the term used on the y axis

Examples: Strings/Water Waves/Light

Question 3

Longitudinal Waves (name of positions, reference used for the y axis, examples)

Answer 3

Oscillations are parallel to direction of travel (left/right)

Compressions - Maximum Pressure
Rarefactions - Maximum Pressure

Pressure is the term used on the y axis

Examples: Sound, Springs

Question 4

Amplitude

Answer 4

Maximum distance from the equilibrium position

Question 5

Wavelength

Answer 5

Distance from two identical points in the wave

Question 6

Frequency (+period)

Answer 6

Number of cycles completed per unit of time (Hz)

Period = 1/frequency

Question 7

Displacement-Distance Graphs

Answer 7

Plots the displacement of every point, at a specific point in time

Demonstrates Wavelength, Amplitude

Shows no indication of time

Question 8

Displacement-Time Graphs

Answer 8

Plots the displacement of a single point, as the wave move pasts it, over time

Demonstrates Peroid, Amplitude

Shows no indication of wavelength

Question 9

Wave Speed

Answer 9

Speed at which a wave transfers its energy

It depends only on the physical properties of the medium it travels through (material, density, temperature)

Question 10

Constructive Interference

Answer 10

Combination of two waves (of the same sign)

Antinode

p.d. = n * wavelength

Question 11

Destructive Interference

Answer 11

Combination of two waves (of different signs)

Node

p.d. = (n - 0.5) * wavelength

Question 12

Doppler Effect

Answer 12

the detected frequency change due to the relative motion between a wave source and detector

Question 13

Does the Doppler Effect have anything to do with wave speed?

Answer 13

No - as the medium has not changed

Question 14

Doppler Effect - Moving Source

Answer 14

Results in ‘bunching of waves’ in front of the source, and, ‘spreading out of waves’ behind the source

Waves in front of the source - increased frequency (waves are closer together)

Waves behind of the source - decreased frequency (waves are further apart)

Question 15

Doppler Effect - Moving Detector

Answer 15

Results in a change in the detected frequency
(and a change in the detected wave speed)

Moving towards the source - increased frequency
Moving away from the source - decreased frequency

no impact on wavelength

Question 16

Reflection of Waves

Answer 16

When some or all of a waves energy is reflected back

If the ending is fixed - the wave will reflect (vertical) & invert (horizontal)

If the ending is free - the wave will just reflect (vertical)

Question 17

Resonance

Answer 17

Occurs when an external force vibrates a system at a frequency that exactly matches one of the natural frequencies

Each forced external vibration will add energy to the system, as there will be a superposition of the travelling wave and its reflection, drastically increasing the amplitude of the oscillations

Question 18

Standing Wave

Answer 18

A wave that has fixed positions of nodes & antinodes

It is the superposition of two waves travelling in the opposite direction with the same frequency and amplitude

The wave will appear not to travel

Question 19

Fundamental Frequency

Answer 19

The lowest possible frequency in a standing wave

Question 20

Requirement to form a standing wave

Answer 20

The string length must be a multiple of wavelength/2 or wavelength/4 (depending on if its a fixed end or not)

Question 21

Harmonic

Answer 21

A standing wave with a frequency equal to an integer multiple of the fundamental frequency

Question 22

Standing Waves (with 2 Fixed Ends)

Answer 22

Has a node at both ends, and an antinode in the middle

Question 23

Standing Wave (with 1 Fixed End)

Answer 23

Requires a node at the fixed end and an antinode at the free end

Reason that antinodes exist at the end - waves reflected at the free end are not inverted (which causes constructive interference)

Question 24

Diffration

Answer 24

The spread of a wave around an obstacle or through a gap

When a wave interacts with the edge of an obstacle, the wave will spread around it rather being blocked

Question 25

Extent of Diffraction

Answer 25

If diffraction is greater than roughly 0.1, then its considered substantiate