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Physics > Chapter 11, 12 - Waves > Flashcards

Chapter 11, 12 - Waves Flashcards

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1
Q

What are Progressive Waves?

A

Progressive waves are waves which transfer energy in the same direction as the wave.

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2
Q

Define Displacement of a Wave.

A

How far the oscillating particle moves from it neutral position, measured in metres.

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3
Q

Define Amplitude.

A

Amplitude is the maximum magnitude of displacement of the oscillating particles, measured in metres.

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4
Q

Define Wavelength.

A

Wavelength is the length of one whole wave cycle (peak to peak), measured in metres.

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5
Q

Define Period of a Wave.

A

The Period of a Wave is the time taken for 1 whole wavelength, measure in seconds.

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6
Q

Define Frequency.

A

Frequency is the number of complete cycles passing a point per second, measured in Hertz.

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7
Q

Define Phase.

A

Phase is a measure of the position of a certain point along the wave cycle, measured in degrees or radian.

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8
Q

Define Phase Difference.

A

Phase Difference is the amount 1 wave lags behind another, measured in degrees or radians.

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9
Q

How are Frequency and Period related?

A

Frequency equals the reciprocal of the period.

f = T⁻¹

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10
Q

What is the equation for Wave Speed?

A

Wave speed (ms⁻¹) = Frequency (Hz) x Wavelength (m)

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11
Q

What are the Key Features of a Transverse Wave?

A
  • Progressive Wave.
  • Oscillations are perpendicular to the direction of Motion.
  • Made up of Peaks and Troughs.
  • Shape is like a Sine Graph.
  • Can Travel in a Vacuum.
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12
Q

What are the Key Feature of Longitudinal Wave?

A
  • Progressive Wave.
  • Oscillations are parallel to the direction of motion.
  • Made up of Compressions and Rarefactions.
  • Cannot travel in a Vacuum.
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13
Q

Define Intensity.

A

Intensity is defined as the rate of flow of energy per unit of area at right angles to the direction of travel of the wave.
Intensity (Wm⁻²) = Power (W) / Area (m²)

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14
Q

How is Intensity proportional to Amplitude?

A

Intensity ∝ (amplitude)²

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15
Q

What Properties do EM Waves have in Common?

A
  • Travel at 3 x 10⁸ ms⁻¹.
  • Transverse waves, so progressive.
  • Oscillating electric and magnetic field perpendicular to each other and the direction of the wave.
  • Can be reflected, refracted, diffracted.
  • Can be Polarised.
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16
Q

What is the Electromagnetic Spectrum?

A 
Royal Marines Invade Vietnam Using X-ray Guns
Radio
Micro
Infrared 
Visible 
Ultra Violet
X-ray
Gamma
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17
Q

What are the Wavelength Boundaries for the EM Spectrum?

A 
Radio: 10⁻¹ - 10⁶
Micro: 10⁻³ - 10⁻¹
Infrared: 7x10⁻⁷ - 10⁻³
Visible: 4x10⁻⁷ - 7x10⁻⁷
Ultraviolet: 10⁻⁸ - 4x10⁻⁷
X-ray: 10⁻¹³ - 10⁻⁸
Gamma: 10⁻¹⁶ - 10⁻¹⁰
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18
Q

What is Polarisation?

A

Polarisation is when you pass a transverse wave through a filter, restricting it to only 1 plane.

19
Q

What happens when you pass a transverse wave through a filter then another filter but rotated 90°?

A

When the wave places through the first filter it will be restricted to 1 plane, however when it passes through the next filter it will be restricted to a different plane, with no energy. Ergo, there will be no remaining wave.

20
Q

How does a polarising grid polarise Microwaves?

A
  • The wavelength of microwave is too long to be polarised by a filter, so a metal grid is used.
  • Electric field excites the electrons in the metal grill.
  • Energy of wave is absorbed and re-emitted on 1 plane in all directions.
  • Only a few of the re-emitted waves are in the same direction as the original wave.
21
Q

What is Diffraction?

A

Diffraction is when a wave passes through a small gap causing the wave to ‘spread’ out.
Diffraction is at its greatest when the gap is width as the wavelength.

22
Q

How can diffraction be investigated?

A
  • Using a ripple tank and an oscillating paddle.

- Using different sized gaps, you can visually see diffraction and what effects it.

23
Q

What is reflection?

A

Reflection is when a wave bounces off a surface boundary causing it to change direction.
The angle of incidence is equal the the angle of reflection.

24
Q

What is Refraction?

A

Refraction is when a wave change direction as it is slowed or sped up as it enters a different medium.
Ray bends towards normal, the ray has entered a slower medium. And Vice Versa.
Angles crossing the boundary are equal, incident.
Angles after crossing the boundary are equal, refraction.

25
Q

Define Refractive Index?

A

Refractive Index is defined as the ratio between the speed of light in a vacuum and speed of light in that medium.
n = c / v

26
Q

What is Snell’s Law?

A 
Snell's Law tells us that:
nsinθ = constant
where n: refractive index, θ: angle to the normal
We can then derive:
n₁sinθ₁ = n₂sinθ₂
27
Q

What is the Critical Angle?

A

At the Critical angle, the wave is refracted and runs alongs the edge the boundary.
When this happens Snell’s Law can be simplified to:
sinC = 1/n
This can be used to find the critical angle.

28
Q

What is Superposition?

A

When two waves of the same type meet and pass through each other, producing a single resultant wave.

29
Q

What is the Principle of Superposition of waves?

A

When two waves meet at a point the resultant displacement at that point is equal to the sum of the displacement of individual waves.

30
Q

What is Interference?

A

When two progressive waves continuously pass through pass through it each other they superpose and form a resultant wave.

31
Q

What is constructive interference?

A

Resultant waves amplitude is greater than the original two waves.

32
Q

What is destructive interference?

A

Resultant waves amplitude is less than the original two waves.

33
Q

What is Coherence?

A

When waves emitted from two sources having a constant phase different. Waves must have the same frequency.

34
Q

What is maxima and minima?

A

Maxima - waves interfere constructively.

Minima - waves interfere deconstructive.

35
Q

How can you calculate wavelength from Young double slit experiment?

A

Wavelength = (Distance between slits x Distance between adjacent fringes) / Distance between screen and slits

36
Q

What are Stationary Waves?

A

When two progressive waves with the same frequency travelling in opposite directions superpose each other. Producing a resultant wave with nodes and antinodes.

37
Q

What are nodes and antinodes?

A

Nodes - A point on a stationary wave where the displacement is always zero.
Antinodes - A point on a stationary with maximum displacement.

38
Q

What is Phase Difference?

A

A measure of the difference in position of two point on a wave. Measure in degrees or radians (where 360* or 2π is a full wavelength).

39
Q

What is Path Difference?

A

Is the difference in distance travelled by the two wave from respective sources to given point on the pattern.

40
Q

What is Fundamental frequency?

A

It is the minimum frequency of stationary waves for a string.

41
Q

How can you create a stationary wave on a string?

A

The string needs tension between 2 fixed points. When the string is plucked a progressive wave travels along the string. The wave reflects, leaving 2 identical progressive waves on the string. These superpose each other, forming a stationary wave.

42
Q

State the differences between Stationary and Progressive waves?

A

Energy Transfer: P waves transfer energy, S waves don’t.
Wavelength: P waves distance of two adjacent points, S waves twice the distance between adjacent nodes.
Amplitude: P waves same amplitude at all points (all particles move the same distance), S waves maximum amplitude occur at antinode and then drops to zero at nodes.
Phase Difference: P waves phase changes across one complete wavelength, S waves all parts between nodes are in phase.

43
Q

How can you get Stationary waves in an air column with closed end?

A

The air at the closed end cannot move, so must be a node.

The air at the open end can move, and the oscillation will have the greatest amplitude. Therefore must be an antinode.

44
Q

How can Stationary waves form in an air column open at both ends?

A

An antinode needs to be at both ends in order to form a stationary wave.

Physics (20 decks)

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