Waves Flashcards
phase difference
The phase difference between two waves is a measure of how much a point or a wave is in front or behind another
And Q are two successive in phase points of tehy are separated by ?
2pi
When are waves in anti-phase ?
When the crest of one wave aligns with the trough of another, they are in antiphase
Simple harmonic motion (SHM) is defined as ?
The motion of an object whose acceleration is directly proportional but opposite in direction to the object’s displacement from a central equilibrium position
The displacement-time graph for an object moving with SHM is a sinusoidal curve if ?
The object starts to oscillate from the equilibrium position.
The displacement-time graph is a cosine curve if ?
The object starts to oscillate from the position of maximum displacement.
Wavefront (2)
A wavefront is a line joining points moving in phase. It is normal ( or perpendicular) to teh direction of energy transfer in Teh wave
Ray
A ray shows teh direction of energy transfer and is perpendicular or a wavefront
Unpolarized light
A light wave that is vibrating in more than one plane is known as unpolarized light
Polarized waves
When a transverse wave is polarised, its electric field is only allowed to oscillate in one fixed plane perpendicular to the direction of motion of the wave
Unpolarized light (long definition)(3)
Unpolarized light consists of short bursts of electromagnetic waves emitted by many different atoms. The electric field directions of these bursts are perpendicular to the direction of wave travel, as in polarized light, but are distributed randomly about it.
transmission axis of the material
The transmission axis of the material is the direction of polarization of the light that passes through the material.
How does polarization work ?(3)
Light waves can be polarised by making them pass through a polarising filter called a polariser. The filter imposes its plane of polarisation on the incident light wave. A polariser with a vertical transmission axis only allows vertical oscillations to be transmitted through the filter (A)
partial plane polarisation (3)
When unpolarised light reflects from a smooth non-metallic surface, partial plane polarisation always occurs
Reflected light is polarised in a plane parallel to the reflecting surface
This means if the surface is horizontal, a proportion of the reflected light will oscillate more in the horizontal plane than the vertical plane
Polarized beams
When beams are polarised, the oscillations of the waves are made to oscillate only in one plane
Reflected beams
When beams are reflected, they bounce back in the direction that they have come in by the same angle
Plane polarisation
Plane polarisation is when the direction of the vibrations stays constant over time, and the vibrations are 100 % restricted in that direction
Partial polarisation
Partial polarisation is when there is some restriction to the direction of the vibrations but not 100 %
Intensity of Polarised Light(2)
The intensity of unpolarised light is reduced as a result of polarisation
If unpolarised light of intensity I0 passes through a polariser, the intensity of the transmitted polarised light falls by a half
polariser
The first filter that the unpolarised light goes through is the polariser
analyser
A second polarising filter placed after the first one is known as an analyser
Why do ultrasound images have lower resolution (in comparison to EM imaging ) in medicine ?(2)
Ultrasound has a larger wavelength than x-rays; [1 mark]
Speed of ultrasound varies with different densities of tissues (Speed varying with greater ratios between tissues means that different tissues in the body (e.g. muscle in your leg compared to your arm) will transmit ultrasound in different waves.)
Damping
The reduction in energy and amplitude of oscillations due to resistive forces on the oscillating system
Light Damping
When oscillations are lightly damped, the amplitude does not decrease linearly
It decays exponentially with time
Critical Damping
When a critically damped oscillator is displaced from the equilibrium, it will return to rest at its equilibrium position in the shortest possible time without oscillating
Heavy Damping
When a heavily damped oscillator is displaced from the equilibrium, it will take a long time to return to its equilibrium position without oscillating
Resistive force
Force that opposes the motion of the oscillator and causes damping
When does maximum amplitude of the oscillations occur ?
The maximum amplitude of the oscillations occurs when the driving frequency is equal to the natural frequency of the oscillator
free oscillation
An oscillation where there are only internal forces (and no external forces) acting and there is no energy input
forced oscillations
Oscillations which are produced by a periodic external force
natural frequency f0
The frequency of an oscillation when the oscillating system is allowed to oscillate freely
driving frequency f
The frequency of the forced oscillations on a system is referred to as the driving frequency f
