Maximum displacement from the equilibrium position
What is frequency?
The number of waves passing a point per second (or number of wave oscillations per second)
What is period?
The time for one complete wave oscillation
Period= 1/frequency
What is wavelength?
The distance between two points that are in phase
What is the wave equation?
What is ment by the phase of a wave ?
The fraction of a cycle where one oscillation lags (or leads) another. Phase (or "phase difference") is often expressed as an angle.
"In phase" means oscillating exactly together (i.e. Phase difference =0^{o})
"In anti-phase" means oscillating in exact opposition (i.e. Phase difference 180^{o})
What is a wave front ?
A wave front is a line on which all the points are in phase
Define a transverse wave
The particles oscillate at right-angles to the direction of energy transfer (e.g. Light)
Define a longitudinal wave
The particles oscillate backwards and forwards in the direction of energy transfer (e.g. sound)
Define a progressive wave
Transmits energy. Where particles are involved: adjacent particles oscillate uot of phase and evergy particle takes its turn to reach the same maximum displacement as the wave passes through.
Define a stationary wave
A wave that stores energy (rather than transmits). Caused when two identical waves pass through each other in opposite directions. Contains nodes and anti-nodes
Define Interference
The combination of two or more waves.
Constructive interference is when waves meet in phase and produce a new oscillation of greater amplitude.
Destructive interference is when waves meet antiphase to produce a new oscillation of smaller amplitude.
State the principle of superposition
The resultant displacement of 2 or more waves is the vector sum of their displacements.
What is path difference ?
It is the difference in distance travelled by two waves to a single point. Used to calculated the phase-difference between the two waves. If the path-difference is half a wavelenght (or an odd number of half wavelengths) the two waves will arrive '180^{o} out of phase. If the path difference is a multiple of the wavelength they arrive in phase.
What is refraction ?
The change in speed of a wave as it passes into a different medium causing a change in wavelength.
What is the Refractive index ?
The Ratio of the speed of the wave i medium 1 to the speed of the wave inÂ medium 2. Also measures the ration of sine (angle of incidence) to sine (angle of refraction).
What is Snell's Law ?
The refractive index of medium 1 to medium 2 = (speed in medium 1)/ (speed in medium 2) = sin(i)/sin(r)
What is total internal reflection ?
Occurs inside a medium when a ray fails to exit (transmit) and is reflected back in because the angle of incidence is greater than the `critical angle`
What is the critical angle ?
It is the greatest angle of incidence that allows a ray to exit a medium and gives an angle of 90^{o} (i.e. "the angle of incidence that causes and angle of refractionÂ = 90^{o}) Common equation used is C=sin^{-1}(1/_{1}μ_{2 }, where _{1}μ_{2 }is the refractive index going from air into the material the wave is now in.
Describe Pulse-Echo
Pulse of speed, v, is emitted, travels a distance, d, reflects off an object and travels back in a time, t. An equation can be used to find v, d or t : v=2d/t (or d=vt/2)
What is the Doppler Effect ?
The apparent change in frequency or wavelength caused by relative motion of source and observer.
Describe Wave-Particle duality:
Electrons show diffraction and interference effect when passed through a crystal lattice. This means electrons are not 'just' particles. They must also have wave properties.
Describe Plane Polarisation
Transvers waves are restricted to oscillate in one plane only and at right angles to the direction of energy transfer.
Describe scan resolution
Detail recorded is limited by wavelength and pulse time. (Shorter the better to avoid poor focus from diffraction spread and from interference between outward and return pulses)
Define Diffraction
The spreading of a wave through a gap or around an obstacle. Maximum diffraction occurs when gap width equals wavelength (More spreading occurs if the wavelength is made larger or the gaqp is made smaller)