All Knowledge Flashcards
What is the definition of SHM
The restoring force acting on the object, when displaced from equilibrium position, is directed towards the centre and proportional to displacement from the equilibrium position
For an object undergoing SHM, where are the velocity and acceleration respectively at there maximum
Velocity - centre point
Acceleration - extremities
State the equation which defines SHM
acceleration = - (constant (angular velocity))*displacement
Describe critical damping
Where the resistance to oscillation of the object is just sufficient to prevent any further oscillations without excessive time taken to return to equilibrium position
Describe overdamping
Where the resistance to oscillation of the object is too great and so the object takes excessive time to return to equilibrium position
Describe underdamping
Where the resistance to oscillation of the object is too little and so the object will oscillate multiple times before coming to rest at equilibrium position
Describe the principle of superposition
The resultant disturbance from two or more waves can be represented by a single periodic wave which is given by the algebraic sum of all the individual waves.
Describe how standing waves are formed
The interference of two waves of equal frequency travelling in opposite directions produces standing waves
What is an anti-node
A point of maximum displacement
What is a node
A point of no displacment
What is the difference between a travelling wave and a stationary wave
A travelling wave radiates energy whereas a standing wave does not. Also, the crests of a standing wave are independent of time whereas the crests of a travelling wave change with time
What condition makes two waves coherent
Constant phase difference
What is the definition of optical path difference
optical path difference = refractive index * geometrical path difference
What occurs when light, travelling through air, reflects off a medium of greater optical density
Pi rad phase change
What occurs when light reflects off a medium of lower optical density
No phase change
When does interference by division of amplitude occur
When a ray of light splits into two beams, by a material of greater optical density,with one ray being transmitted and other ray being reflected. When focused by an eye, both rays will combine and interfere.
What is the condition for constructive interference in thin-film interference
2nt = (m+1/2)*wavelength
What is the condition for destructive interference in thin-film interference
2nt = m*wavelength
Why does a puddle with oil on it appear multi-coloured in the sunlight
The oil on the puddle acts as a thin-film hence it produces interference by division of amplitude. Sunlight is a continuous source and do is made up of all wavelengths of light which will all refract through oil differently produced coloured fringes. Also, differences in thickness of the oil produce a complex pattern of fringes.
Why can an extended (non-coherent) source be used for interference by division of amplitude
Division of amplitude splits a single wave into two before recombining. The two beams that result from splitting a wave will always be coherent which means that we do not require a source of two coherent waves as only one wave is required.
Why do glasses with a non-reflective coating appear purple
Complete cancellation of reflected light only occurs at a specific wavelength. For maximum coverage, this wavelength is often chosen in the middle of the visible spectrum. Hence, the wavelengths at the extremities of the spectrum, purple and blue, do not undergo destructive interference and instead combine producing a purple-reddish colour on the glasses.
What kind of source must be used for interference by division of wavefront
A point source
What is the difference between interference by division of amplitude and interference by division of wavefront?
Interference by division of amplitude involves splitting a single wave which is then combined producing interference effects whereas interference by division of wavefront involves the interference of two separate, coherent waves.
Describe the Young’s Slit Experiment
A monochromatic source is incident on the double slit producing two secondary sources by division of wavefront. The slit separation must be in the order of the wavelength of light used and the distance to the screen must be much greater. The two secondary sources act as point sources and the overlap of the beams will produce an interference pattern.
What is the difference between unpolarised and linearly polarised light?
The electric field vector of unpolarised light has equal probability of oscillating in every direction whereas polarised light only oscillates in a single plane.
What type of waves can be polarised?
Transverse waves
Describe Brewster’s Law of Polarisation
Brewster’s Law says that at a certain angle of incidence, the light reflected off a dielectric medium will be completely polarised. At all other angles, the light will be partially polarised.
What is the angle between the reflected and transmitted ray at the Brewster Angle?
90 degrees
Describe some applications of polarisation
Reduction of glare by polaroid sunglasses and camera lenses. When sunlight is reflected off the road or a body of water it will be partially polarised in the horizontal transmission axis therefore, a polariod in the vertical transmission axis will block glare from the road or water.
