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A Level Physics > Waves > Flashcards

Waves Flashcards

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1
Q

Continuous Wave definition

A

Constant amplitude and frequency

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2
Q

Wavelength definition

A

The distance between any point and the next identical point

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3
Q

Frequency definition

A

Number of oscillations in one second

Measured in Hz

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4
Q

Frequency and Time equation

A

f = 1/T

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5
Q

Speed/Frequency/Wavelength equation

A 
c = f * wavelength
m/s = Hz * m
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6
Q

Dispersion definition

A

Waves separate out whilst travelling through a medium

Due to different wavelengths travelling at different speeds

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7
Q

Displacement definition

A

Distance from the centre of the oscillation to the particle

Vector, so can be negative

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8
Q

Amplitude definition

A

Maximum displacement

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9
Q

Energy/Amplitude equation

A

Energy is directly proportional to amplitude squared

E = k A^2

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10
Q

Out of phase definition

A

Two waves with same frequency and wavelength, but one is shifted compared to the other

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11
Q

Single slit diffraction pattern

A

Central maxima

Decreasing height of maxima as you get further from centre

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12
Q

Double slit interference

How to increase fringe separation

A

Distance from slits to screen is increased
Wavelength of light used is increased
Slit spacing (distance between centres of slits) is decreased

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13
Q

Fringe separation equation

A 
w = λD/s
w = fringe separation
λ = wavelength of light
D = distance from slits to screen
s = slit spacing
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14
Q

Slit spacing definition

A

Distance between centres of slits

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15
Q

Why are fringes formed

A

Interference of light

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16
Q

Why are bright fringes formed from double slit

A

Light waves from each slit are in phase

Path difference = lambda

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17
Q

Why are dark fringes formed from double slit

A

Light waves from each slit arrive 180º out of phase

path difference = lambda/2

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18
Q

Why are lasers used in double slit experiments

A

Coherent source of light => no need for a single slit before.
Photons in a laser beam are in phase with each other

Highly monochromatic, meaning its wavelength can be calculated to within a nanometre

19
Q

What happens when white light is used for double slits

A

Central fringe is white
Each component colour of white light produces its own fringe pattern
Each pattern is centred on the screen at the same position

20
Q

Principle of superstition

A 
Exact moment when 2 waves meet
Crest + crest = super crest
Trough + trough = super trough
Crest + trough = 0 displacement
- If waves aren't of equal magnitude, crest + trough = minimum
21
Q

In phase definition

A

Two waves superimpose constructively

22
Q

Anti phase definition

A

two waves superpose destructively

23
Q

Node definition

A

Resultant wave = 0 displacement

No oscillation

24
Q

Anti-node definition

A

Resultant waves has largest amplitude

Maximum oscillation

25
Q

Distance between nodes

A

= distance between antinodes

= wavelength/2

26
Q

Difference between transverse and longitudinal waves

A

Transverse:
vibrations act perpendicular to direction of energy transfer

Longitudinal:
vibrations occur parallel to direction of energy transfer

27
Q

How is light proven as a wave?

A

Interference
- Used if the size of the object is comparable to the wavelength of the light

Or diffraction and polarisation

28
Q

How is light proven as a particle?

A

Photo-electric effect

- Used if the energy is comparable to the energy of the photon (E=hf)

29
Q

Which experiment(s) prove light could be both a wave and a particle?

A

Reflection

Refraction

30
Q

Emission vs absorption

A
  1. Hot object will emit a continuous spectrum of light
  2. Cool gas will absorb some of the photons with specific energies, exciting the orbital electrons
  3. Orbital electrons will return to the ground state and emit photons with the same frequency
31
Q

Forced vibrations definition

A

Vibrations/oscillations of a system subjected to an external periodic force

32
Q

Resonance definition

A

System vibrates such that its velocity is in phase with the periodic force
An oscillating body that is not resonating will return to its natural frequency when the forcing vibration is removed

33
Q

Damped oscillations definition

A

Oscillations that reduce the amplitude for ALL frequencies due to the presence of resistive forces such as friction and drag

  1. Lightly dampened system, amplitude of oscillations decreases gradually
  2. Heavily dampened system displaced from equilibrium then released, the system slowly returns to equilibrium without oscillating
  3. Critically damped system, it returns to equilibrium in the least possible time without oscillating
34
Q

As an applied frequency to a system increases…

A
  1. The amplitude of oscillations increases until it reaches a maximum amplitude at a particular frequency, and then the amplitude decreases again
  2. Phase difference between DISPLACEMENT AND THE PERIODIC FORCE increases from 0 to pi/2 at maximum amplitude, then from pi/2 to pi as the frequency increases further
35
Q

Resonant frequency definition

A

The frequency of a system at the maximum amplitude

36
Q

For an oscillating system with little/no dampening, at resonance…

A

The applied frequency of the periodic force = the natural frequency of the system

37
Q

Diffraction grating definition

A

A plate with may closely ruled parallel slits on it

38
Q

How is the angle of diffraction between each transmitted beam and the central beam increased (diffraction grating)

A

Light with longer wavelength used (e.g. blue filter instead of red filter)
Grating with finer slits is used

39
Q

Diffraction grating equation

A

d * sin theta = n * lambda

d = slit separation (number of slits/metre = 1/d)
theta = angle between central maxima and nth order
n = order number
lambda = wavelength of light used
40
Q

What does an increase of the number of slits do (diffraction grating)

A

Narrower peaks
More precise measurements
Increased intensity
Higher concentration of light

41
Q

Electromagnetic spectrum

A

Smallest frequency => highest frequency
Largest wavelength => shortest wavelength
Radio waves - microwaves - Infared - visible - UV - X-Ray - Gamma Ray

Visible light:
Violet shortest wavelength, red longest
BLUE HAS SHORTER WAVELENGTH THAN RED

42
Q

Types of spectra

A

Continuous
Shows all colours
Most intensive part of the spectrum depends on temperature
- Hotter the light source, the shorter the wavelength of most intensive part
Means that by measuring the wavelength of most intensive part, we can measure the temperature of the light source

Line emission
Glowing gas in a vapour lamp/discharge tube emits light at specific wavelengths
Characterised by the chemical element that produced the light

Line absorption
Continuous spectrum with narrow dark lines at certain wavelengths
Due to elements in glowing gas, which absorb light of the wavelengths they can emit, so the transmitted light is missing these wavelengths

43
Q

Young’s double slit

How is the pattern formed on the screen?

A

Each slit diffracts light, emitting waves
Two slits act as coherent sources of light
Proves light is a wave as interference is a wave property
Bright fringes formed when light from one slit reinforces light from the other
Light from slits is in phase at a maxima, causing reinforcement
Path difference to bright fringe = n lambda (whole number of wavelengths)
Path difference to a dark fringe = (n+1/2) lambda (half wavelengths)

A Level Physics (8 decks)

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