module 4.4 waves mock revision Flashcards
Progressive Wave
A series of vibrations that transfers energy from one place to another.
Longitudinal Wave
A wave where particle oscillations are in the direction of wave propagation. E.g. Sound Waves
Transverse Wave
A wave where particle oscillations are perpendicular to the direction of wave propagation
Displacement
The distance any part of a wave has moved from its mean or rest position
Amplitude
The maximum displacement of a wave from its mean or rest position
Wavelength
The smallest distance between two points on a wave that are in phase
Period
The time taken for one complete pattern of oscillation
Frequency
The number of oscillations at a given point per unit time
Speed of a wave
Distance travelled by the wave (energy) per unit time
frequency = 1/period
period = 1/frequency
𝑆𝑝𝑒𝑒𝑑(𝑣) =𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑑)/ 𝑇𝑖𝑚𝑒 (𝑡)
→ 𝑆𝑝𝑒𝑒𝑑(𝑣) = 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑀𝑜𝑣𝑒𝑑 (𝜆) /𝑇𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 (1/𝑓)
v = 𝑓𝜆
Reflection
When waves rebound from a barrier, changing direction but remaining in the same medium.
Refraction
When waves change direction when they travel from one medium to another due to the difference in wave speed in each medium.
Diffraction
When a wave spreads out after passing around an obstacle or through a gap
radio waves
used for communication, tv radio
microwaves
used in mobile phones, microwave ovens,
communication, heating
infrared
heating, remote controls
visible light
sight
uv
tanning, counterfeit detection
x-rays
x-ray photography, security scanners, kill cancer cells
gamma rays
cancer treatmet, sterilisation of medical instruments
gamma rays
cancer treatment, sterilization of medical instruments
the role of sunscreen
Protects the skin from sunburn by absorbing UV-B radiation
UV-B also produces vitamin D
All electromagnetic have some properties in common
They all travel at the speed of light in a vacuum and slower speeds in other media
They are transverse waves consisting of vibrating electric and magnetic fields. The electric and magnetic fields are at right angles to each other and the direction of travel.
Like all waves they can be reflected, refracted and diffracted and can undergo interference.
Like all ways they obey v=fλ (v = velocity, f = frequency, λ = wavelength)
Like all progressive waves, progressive EM waves carry energy
Like all transverse waves EM waves can be polarised
Some Properties Vary Across the EM Spectrum
The longer the λ the more obvious the wave characteristics
Energy is directly proportional to the frequency (E = hf)
The higher the energy the more dangerous the wave
The lower the energy the further from the nucleus it comes from.
- Gamma radiation comes from inside the nucleus.
- X-rays to visible light come from energy level transitions in atoms.
- Infrared radiation and microwaves are associated with molecules.
- Radio waves come from oscillations in electric fields.
Plane-Polarised Wave
A transverse wave oscillating in only one plane
Polarisation
The process of turning an un-polarised wave into a plane polarised wave.
wave phenomena that apply to both longitudinal and transverse waves
diffraction
refraction
superposition (interference)
a wave phenomenon that applies only transverse waves but not longitudinal waves.
Polarisation
how polaroid sunglasses can prevent glare from light reflected from a water surface
light reflected from water surface is partially plane polarised
alignment of polaroid lens is at right angles to plane of polarisation of reflected light
polarised reflected light is not transmitted by polaroid lens
Malus’s law
A = A0Cosθ so I = I0Cos2θ
I = 1/2I0 after first filter as ½ light goes through.
Describe and explain an experiment to demonstrate the polarisation of microwaves
place microwave transmitter and receiver facing each other
place two polarising filters (metal grid with bars ~1cm apart) across path of beam
observed signal on receiver is maximum intensity when polarising filters are parallel
the first filter polarises the beam, the beam can pass through the second filter because the plane of polarisation of the beam matches the alignment of the filter.
rotate polarising filter 90^ from parallel to crossed
observed signal on receiver drops to minimum intensity (zero) when polarising filters are
crossed
the beam cannot pass through the second filter when the plane of polarisation of the beam is at 906^ to the alignment of the filter
Principle of Superposition
When two or more waves meet at a point the resultant
displacement at that point is the vector sum of the displacements due to each wave.
Interference
The vector addition of two or more waves (superposition) that results in a new wave pattern
Coherence
Two waves with a constant phase relationship (Same f & λ)
Phase Difference (φ)
The angular distance by which one particle leads or lags behind another particle in its pattern of oscillation.
Path Difference
The distance between the distances travelled from their sources by two waves meeting at a point.
Constructive interference
If two waves exist at the same point and are in phase, the amplitude of the resultant wave will be the sum of the amplitudes of the individual waves
Destructive interference
If two waves exist at the same point and are anti-phase, the amplitude of the resultant wave will be zero as the waves cancel each other out.
𝐼𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑦 =
𝐼𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑦 = 𝑃𝑜𝑤𝑒𝑟/ 𝐶𝑟𝑜𝑠𝑠 𝑆𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝐴𝑟𝑒𝑎
𝐼𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑦 ∝ 𝑎𝑚𝑝𝑙𝑖𝑡𝑢𝑑𝑒2
n = d sin 0
n is order of maximum [ no units ]
λ = wavelength [ m ]
d is spacing between slits [ m ]
0 is angle at which maximum occurs [ degrees ]
Node
A point that always has zero amplitude along a stationary wave, caused by destructive interference
Antinode
A point of maximum amplitude along a stationary wave, caused by constructive interference
Fundamental Mode of Vibration (Frequency)
The lowest frequency in a harmonic series where a stationary wave forms.
Harmonics
Stationary waves for a particular system with higher frequencies than the fundamental.
how a stationary wave is formed
wave travels to end and is reflected
reflected wave superposes with incident wave to produce a resultant wave
at certain points always destructive interference to produce nodes
at certain points always constructive interference to produce antinodes
phase difference
how far ‘out of step’ the oscillations at two points
on the wave are
stationary wave
a wave which traps/stores energy (in pockets)
has nodes and antinodes
how is a stationary wave formed
the wave is reflected
it interferes/superposes with the incident wave
to produce a resultant wave with nodes and antinodes/no energy transfer
