Chapter 11, 12 - Waves Flashcards
What are Progressive Waves?
Progressive waves are waves which transfer energy in the same direction as the wave.
Define Displacement of a Wave.
How far the oscillating particle moves from it neutral position, measured in metres.
Define Amplitude.
Amplitude is the maximum magnitude of displacement of the oscillating particles, measured in metres.
Define Wavelength.
Wavelength is the length of one whole wave cycle (peak to peak), measured in metres.
Define Period of a Wave.
The Period of a Wave is the time taken for 1 whole wavelength, measure in seconds.
Define Frequency.
Frequency is the number of complete cycles passing a point per second, measured in Hertz.
Define Phase.
Phase is a measure of the position of a certain point along the wave cycle, measured in degrees or radian.
Define Phase Difference.
Phase Difference is the amount 1 wave lags behind another, measured in degrees or radians.
How are Frequency and Period related?
Frequency equals the reciprocal of the period.
f = T⁻¹
What is the equation for Wave Speed?
Wave speed (ms⁻¹) = Frequency (Hz) x Wavelength (m)
What are the Key Features of a Transverse Wave?
- 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.
What are the Key Feature of Longitudinal Wave?
- Progressive Wave.
- Oscillations are parallel to the direction of motion.
- Made up of Compressions and Rarefactions.
- Cannot travel in a Vacuum.
Define Intensity.
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)
How is Intensity proportional to Amplitude?
Intensity ∝ (amplitude)²
What Properties do EM Waves have in Common?
- 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.
What is the Electromagnetic Spectrum?
Royal Marines Invade Vietnam Using X-ray Guns Radio Micro Infrared Visible Ultra Violet X-ray Gamma
What are the Wavelength Boundaries for the EM Spectrum?
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
What is Polarisation?
Polarisation is when you pass a transverse wave through a filter, restricting it to only 1 plane.
What happens when you pass a transverse wave through a filter then another filter but rotated 90°?
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.
How does a polarising grid polarise Microwaves?
- 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.
What is Diffraction?
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.
How can diffraction be investigated?
- Using a ripple tank and an oscillating paddle.
- Using different sized gaps, you can visually see diffraction and what effects it.
What is reflection?
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.
What is Refraction?
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.
Define Refractive Index?
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
What is Snell’s Law?
Snell's Law tells us that: nsinθ = constant where n: refractive index, θ: angle to the normal We can then derive: n₁sinθ₁ = n₂sinθ₂
What is the Critical Angle?
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.
What is Superposition?
When two waves of the same type meet and pass through each other, producing a single resultant wave.
What is the Principle of Superposition of waves?
When two waves meet at a point the resultant displacement at that point is equal to the sum of the displacement of individual waves.
What is Interference?
When two progressive waves continuously pass through pass through it each other they superpose and form a resultant wave.
What is constructive interference?
Resultant waves amplitude is greater than the original two waves.
What is destructive interference?
Resultant waves amplitude is less than the original two waves.
What is Coherence?
When waves emitted from two sources having a constant phase different. Waves must have the same frequency.
What is maxima and minima?
Maxima - waves interfere constructively.
Minima - waves interfere deconstructive.
How can you calculate wavelength from Young double slit experiment?
Wavelength = (Distance between slits x Distance between adjacent fringes) / Distance between screen and slits
What are Stationary Waves?
When two progressive waves with the same frequency travelling in opposite directions superpose each other. Producing a resultant wave with nodes and antinodes.
What are nodes and antinodes?
Nodes - A point on a stationary wave where the displacement is always zero.
Antinodes - A point on a stationary with maximum displacement.
What is Phase Difference?
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).
What is Path Difference?
Is the difference in distance travelled by the two wave from respective sources to given point on the pattern.
What is Fundamental frequency?
It is the minimum frequency of stationary waves for a string.
How can you create a stationary wave on a string?
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.
State the differences between Stationary and Progressive waves?
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.
How can you get Stationary waves in an air column with closed end?
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.
How can Stationary waves form in an air column open at both ends?
An antinode needs to be at both ends in order to form a stationary wave.
