Waves - The better set of flashcards
How does TIR transmit information along an optic fibre?
light fibre consists of core and cladding with a lower refractive index or optical density. Light is incident at an angle greater than the critical angle which results in TIR.
What happens to the wavelength, frequency and speed of light when a ray of light travels from air into glass?
Wavelength = decreases Frequency = stays the same Speed = decreases
Equation to find out diffracted angles?
N1SINX1 = N2SINX2
State the purpose of the outer sheath in an optical fibre?
Prevent physical damage to the fibre and strengthen it.
Describe the structure of step-index optical fibres outlining the purpose of the core and the classing?
Core is transmission medium for EM waves to progress by total internal reflection, the cladding provides a lower refractive indies to ensure TIR occurs and offered protection of boundary from scratching which could lead to light leaving the core.
What is a longitudinal wave?
A wave with parallel oscillations - sound waves and P waves
What is a transverse wave?
A wave with perpendicular oscillations and it can be polarised! such as electromagnetic waves and S waves
Use wave theory to explain how a pattern of bright and dark patches are formed…
Slits act as coherent sources (1) waves diffract at the slits (1) the waves superpose (1) and bright patches are the constructive interference (1) whilst the dark patches are destructive interference (1)
What is monochromatic light?
Light of a single wavelength
How is a stationary wave formed?
The result of the interference of the two waves above is a new wave pattern known as a standing wave pattern. Stationary waves are produced whenever two waves of identical frequency interfere with one another while traveling opposite directions along the same medium Nodes are produced when crest meets tough and antinodes are produced when a crest+crest or trough+trough
Explain how Young’s interference fringes are formed and why the first slit should be narrow and why the second slits should be coherent.
A narrower slot gives wide diffraction which will ensure that the second slits are illuminated. A narrow first slit also provides coherent light sources so the second slits are illuminated by the same source giving the same wavelength. Constructive and destructive interference occurs.
Properties of a laser light:
Monochromatic (waves of single wavelength)
Collimated (produces an appromixmately parallel beam)
Coherent (waves produced in constant phase)
Polarised (vibrations in one plane only)
Displacement
The distance and direction of a particle from equilibrium position.
Amplitude
Maximum displacement of a vibrating particle
Wavelength
Shortest distance between two particles in phase
Frequency
Number of wave cycles occurring each second
Wavespeed
Distance travelled by a wave each second
Phase difference
Measured in degrees or radians ( the amount by which one wave lags behind another wave)
Path difference
The differences in lengths of 2 waves
Progressive waves
Waves whose oscillations travel and transfer energy.
Give an example of how polarisation can be used
Polarisation can be used in things such as Polaroid sunglasses to reduce glare or in a camera to enhance an image
what is superposition?
The point where waves meet - the total displacement at a point is equal to the sum of the individual displacements at that point
Is energy transferred in stationary waves
No
What is diffraction?
Is the spreading out of waves when they pass through a gap or over an edge - increasing the lit width creates an intense but narrow central maximum and vice Verda
In diffraction gratings…
The more slits, the sharper the interference pattern. Constructive interference patterns are called maxima
N = C1/C2
The absolute refractive index of a material measured by how much it slows down light and is a ratio.
What must happen for TIR to occur?
The light must travel form a more optically dense medium to a less optically dense medium. The angle of incidence of the light ray must exceed the critical angle of the interference
Step- index optical fibres…
Core = high refractive index (more dense) Cladding = pow refractive index (less dense)
What is modal dispersion?
Some rays take longer to get to the receiver based on the path they take.
What is material dispersion?
Different frequencies travel at different speeds in the core which means they reach the receiver at different times.
