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Waves Flashcards

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1
Q

Define frequency and its unit

A

Number of waves passing through a point per second
Hertz

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2
Q

Define wavelength

A

Distance between two adjacent points anywhere on a wave
Metres

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3
Q

Define amplitude

A

Maximum displacement from equilibrium position

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4
Q

Explain why it is important to correctly align the aerial of a TV in order to receive the
strongest signal

A

Radio waves are often polarised
Aerial must be aligned in same plane of the wave

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5
Q

Longitudinal wave

A

wave in which the particles oscillate parallel to the direction of the wave travel (and energy transfer)

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6
Q

Transverse wave

A

Oscillates parallel

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7
Q

What is the fundamental frequency?

A

The first harmonic

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8
Q

What causes a stationary wave?

A

Same amplitude
Same frequency
Opposite directions
Superpose

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9
Q

What is polarisation?

A

When there is only one plane of oscillation

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10
Q

State a use of polarisation

A

Sunglasses - reduces intensity by removing many planes of oscillation
Privacy screens- light from monitors polarised, filter prevents different viewing angles

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11
Q

Constructive interference

A

R=nlamda
Path difference of a whole wavelength

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12
Q

Destructive interference

A

R=n+1lamda
Path difference of a half wavelength

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13
Q

Slit spacing equation

A

d=W/n
Width/number of lines

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14
Q

Single slit diffraction

A

Double width central maxima
Central white light, rest coloured/ dark and light fringes
Equally spaced
Slit width must be approximately same as wavelength

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15
Q

Diffraction grating

A

Intense narrow lines (sharper and brighter)
Central maxima is the 0 order

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16
Q

Youngs double slit experiment with monochromatic loght

A

Shine a coherent light source through 2 slits roughly same size as wavelength so light diffracts
Each slit acts as a coherent light source make areas of light and dark
Light fringe is formed when they interfere constructively and are in phase
Dark fringe is formed when they are completely out of phase so interferes destructively

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17
Q

Laser safety

A

Wear laser safety goggles
Do not shine at reflective surfaces
Warning sign
Never shine at people

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18
Q

Proof of em radiation as wave

A

Youngs slit (diffraction and interference)

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19
Q

What is diffraction?

A

The spreading out of waves as they pass through or around a gap.
Greatest diffraction when gap is equal size
If gap smaller then most light reflects

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20
Q

If you use white light why do you see a range of colours diffracting?

A

Different wavelengths of light have different wavelengths which diffract different amounts

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21
Q

Increasing slit width….

A

Decreases amount of diffraction

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22
Q

Increasing the wavelength of light…..

A

Increases the amount of diffraction

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23
Q

Uses of diffraction gratings

A

Line absorption spectra (split light from stars)
X-ray crystallography

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24
Q

What does monochromatic light mean?

A

Light of same frequency

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25
What does coherent mean?
Constant phase difference
26
Define the phase of a wave
Its position in the cycle Radians/degrees/fractions of a cycle
27
Define phase difference
how much a point or a wave is in front or behind another
28
What is a progressive wave?
A wave that transfers energy form one point to another
29
Examples of longitudinal waves
Slinky Sound wave
30
Example of a transverse wave
EM Waves Water Mexican
31
How do you receive the best signal from a tv aerial
Point it towards the source of waves so it is in the same plane. Therefore they will receive strongest signal
32
Describe constructive interference
Crests or troughs are aligned Waves are in phase (path difference of n) Double the amplitude
33
Describe destructive interference
Crest and trough align Antiphase (path difference of n+0.5) Waves must be coherent
34
Features of stationary wave
No energy transfer Opposite directions of waves Nodes and anti nodes
35
Example of stationary waves
Microwaves ( microwave probe can find nodes and anti nodes, or put a chocolate in but don’t rotate) Harmonics Speakers (speaker at end of tube of glass, nodes will cause powder to sit still, anti nodes will cause powder to shake)
36
Equation for mu
Mass per unit length So density x area
37
Definition of coherence
Same freq, amplitude, same wavelength, same polarisation Constant phase relationship
38
Example of a coherent light source and one that is not
Laser is Light bulb is not
39
What is diffraction
The bending of a wave as it moves through a narrow opening or around an obstacle
40
How to increase diffraction
Smaller gap (closer to wavelength) Increase the wavelength Make obstacle a closer size to wavelength
41
When will the most diffraction occur
When gap equals the wavelength of the light
42
How to decrease diffraction?
Wider gap Increase frequency (decrease wavelength)
43
Diffraction pattern of single slit
Bright central maxima, double the width of the rest Ares of bright ( constructive) and dark (destructive) Intensity decrease over time
44
What order is the central maxima
0
45
What happens if white light is used
Spectra created as light has different wavelengths Violet diffracts least so closest to centre Red diffracts most so furthest from centre Central maxima still white
46
What happens if you increase slit width on diffraction pattern
Less diffraction but narrower and more intense maxima
47
What happens if pay increase the wavelength
More diffraction occurs and the central maxima is less intense
48
What is a diffraction grating
Lots of equally spaced lots of same width. More rays reinforcing pattern so it is sharper and brighter
49
Why use a grating with more slits?
There are more rays reinforcing pattern so it is easier to measure fringes as narrower, sharper and brighter
50
What can fringe spacing formula be used for?
Double slit
51
What can the dsintheta=nwavelength
Diffraction gratings (Single slit)
52
How do Polaroid glasses reduce glare from puddle?
When light is reflected from a reflective surface e.g. the surface of water or a wet road, it undergoes partial plane polarisation This means if the surface is horizontal, a proportion of the reflected light will oscillate more in the horizontal plane than the vertical plane Therefore, polaroid sunglasses are useful in reducing the glare on the surface of the water (or any reflective surface) as the partially-polarised light will be eliminated by the polarising filter As a result of this, objects under the surface of the water can be viewed more clearly
53
What is a free vibration?
Involve no energy transfer to or from surroundings If you release a mass on a string it will oscillate at resonant frequency It should oscillate forever In practice this does not happen
54
What is a forced vibration?
External driving force Driving frequency much less than natural frequency of oscillator than driver and oscillator in phase If driving frequency much greater than natural frequency, oscillator can’t keep up and so out of phase (antiphase)
55
When does resonance occur?
Driving frequency = natural frequency
56
What happens when driving frequency = natural frequency ?
More and more energy transferred to system and so system oscillates with increasing amplitude The two are 90 degrees out of phase
57
What are some examples of resonance?
Radio tuned so electric circuit resonates at same frequency of radio station Glass resonates when driven by a sound wave at right frequency Column of air resonates in an organ pipe, driven by the motion of air at base. This creates a stationary wave. Swing resonates if pushed at natural frequency
58
What are the four types of damping?
Light Heavy Critical Over
59
What is damping?
Damping forces act causing amplitude to reduce over time. These can be forces like friction or air resistance
60
How does light damping compare to heavy damping?
Light damping causes amplitude to reduce by a small amount each period Heavy damping takes much less time to stop oscillations
61
What does the period of a pendulum not depend on?
Mass
62
What is critical damping?
Reduces amplitude in quickest way possible
63
What is over damping?
They take longer to return to equilibrium as damping is too heavy
64
Definition of SHM
An oscillation in which the acceleration of an object is directly proportional to its displacement from its equilibrium position, and it’s directed towards the equilibrium

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