Waves Flashcards

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1
Q

For a moving observer: When do you add or subtract Uo

A

Towards: Add
Away: Subtract

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2
Q

For a moving source: when do you add and subtract Us

A

Towards: Subtract
Away: Add

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3
Q

What is a travelling wave?

A

A wave that transfers energy but not matter

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4
Q

What is a transverse and longitudinal wave

A

Transverse: Particles oscillate perpendicular to direction of energy transfer

Longitudinal: particles oscillate parallel to direction of energy transfer

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5
Q

What is time period and frequency

A

Time Period: Time taken for 1 complete oscillation

Frequency: Number of oscillations that pass a point in 1s

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6
Q

For a Displacement-Distance Graph:

Which direction shows a positive and negative displacement

What can you find with the graph

A
  1. Positive = Right
    Negative = Left
  2. Wavelength and amplitude
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7
Q

For a Displacement-Time Graph:

What does the graph represent

What can you find using the graph

A
  1. Movement of 1 particle
  2. Amplitude, Time Period, Frequency
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8
Q

Phase Difference:

What is the definition

What multiples of pi means is in phase and completely out of phase

A
  1. Fraction of a wavelength that one lags
    the other
  2. In phase: 2π, 4π…
    Completely out of phase: 1π, 3π…
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9
Q

What are rays and wavefronts

A

Wavefront: Shows parts of waves that are
in phase with each other

Rays: Are perpendicular to the wavefronts
and show direction of energy
transfer

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10
Q

What is refraction

A

Change of wavelength, speed and direction of a wave as it passes into a new medium

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11
Q

What is the equation for index of refraction

A

n1 = c / v1

c = speed of light in vacuum
v1 = speed of light in medium

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12
Q

What are the 6 things that happens when a wave meets a boundary

A

Transmission
Reflection
Refraction
Diffraction
Absorption
Scattering

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13
Q

What happens to speed, wavelength, change in angle and frequency as a wave enters a dense medium

A

Speed: Decreases
Wavelength: Decreases
Change in Angle: 0̷1 > 0̷2
Frequency: Same

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14
Q

What is the angle of refraction at the critical angle

A

90°

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15
Q

What is superposition

A

When 2 or more waves cross, the resultant displacement equals the vector sum of individual displacements

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16
Q

What is interference

A

The result of superposition of 2 or more waves

17
Q

What is constructive/destructive interference

A

When 2 waves meet to make a larger/smaller displacement

18
Q

What happens if interference occurs between:

2 Crests
2 Troughs
Crest and Trough

A

2 Crests: Constructive, in phase
2 Trough: Constructive, in phase
Crests and Trough: Destructive,
Completely out of
phase

19
Q

What does it mean for 2 wave to be coherent

A

If they have a constant phase difference between them

Requires both to have the same speed, frequency and wavelength

20
Q

How is a standing wave formed

A

When 2 coherent waves with the same amplitude, travelling in opposite directions, interfere with each other, superposition occurs

21
Q

What are nodes and antinodes

A

Nodes: points of zero displacement
Antinodes: points that oscillate with
maximum displacement

22
Q

What points on a standing wave are:
In phase
Completely out of phase

A

In phase: Area between 2 nodes
Completely out of phase: Sides next to a
node

23
Q

Let n be the harmonic number and c be wave speed

What is the equation for Length and Frequency for:
2 Closed Ends
2 Open Ends
1 Open and 1 Closed End

A

2C: L = 0.5nλ
F = nc/2L

2O: L = 0.5nλ
F = nc/2L

1O1C: L = 0.25nλ
F = nc/4L

24
Q

What does a closed and open end form

A

Closed: Node
Open: Antinode

25
Q

What is the Doppler effect

A

The apparent change in frequency of a wave due to relative motion between source and observer

26
Q

How does measured wavelength, apparent wave speed and apparent frequency change with a:

Moving Source
Moving Observer

A

MS: Changes, Same, Changes
MO: Same, Changes, Changes

27
Q

What are the conditions for constructive/destructive interference

A

Constructive:
Must be in phase (2nπ)
Path difference must be nλ

Destructive:
Must be out of phase [(2n+1)π]
Path difference must be (n+0.5)λ

Both:
Both waves must have the same frequency and wavelength
Waves must be coherent