Waves Flashcards
What is the phase difference between between two points on a wave?
It’s the difference in their positions in the wave’s cycles
Describe the phase difference between two waves
It’s how much one lags behind the other
Describe stationary waves
All points between consecutive nodes are vibrating in phase as they all reach their maximum displacement at the same time
What is superposition?
When similar waves meet the total displacement of the wave is the vector sum of the individual displacements
What is the first harmonic?
The lowest frequency at which a standing wave is formed, it has an antinode in the centre. It has 1/2 a wavelength
What happens when you blow into a pipe like a flute?
A stationary wave is formed in the pipe with nodes at the closed ends and antinodes at the open ends.
What is a polarised wave?
A transverse wave whose oscillations are confined to one plane
Name two uses of polarising filters
Sunglasses to reduce glare
TV signals, the alignment of the receiving aerial must match the polarisation direction of the transmitted waves
When is diffraction most noticeable?
When the aperture is a similar size to the wavelength of the wave
Describe the diffraction pattern from a single slit
There is a central maxima which is twice as wide and much more intense than the other maxima. The smaller the gap, the wider the central maxima.
What happens when white light passes through the slit?
Each colour diffracts a different amount which leads to a rainbow effect in all but the central maximum
What does it mean if two waves are coherent
Two sources of waves are coherent if they have the same frequency, are polarised in the same plane and they maintain a constant phase difference
When does constructive interference occur?
When the path difference from the source is a integer number of wavelengths
When do you get destructive interference?
When the path difference is a half number of wavelengths (n+0.5) wavelengths
Define w=λD/s
Fringe spacing=wavelength×distance between slits and screen/spacing between slits
Define dsinx=nλ
Distance between slits×sin(angle between incident beam and nth maximum)=order of maximum×wavelength
d=1/number of slits in 1m
What are the two layers of optical fibres?
The inner layer, the core, where the light is transmitted and the outer layer, the cladding, which protects the cable
How does light pass through the fibre?
Total internal reflection
What is the critical angle?
The angle of incidence at which the light is refracted along the boundary
What is snell’s law
n1sinx1=n2sinx2
Critical angle equation?
Sinxc=n2/n1
What are 4 problems that can occur with optical fibres?
Absorption, some of the signals energy is absorbed by the material of the fibre which reduced the signal amplitude
If a fibre is bent too sharply, the angle the ray makes with the normal will be altered and the light can strike the cladding at less than the critical angle and leave the fibre
Modal dispersion, rays enter at different angles so they take different times to leave the fibre, use a narrower fibre
Chromatic dispersion, white light splits into a spectrum, use monochromatic light
