Waves Flashcards
All electromagnetic waves are what type of waves?
Transverse waves
All electromagnetic waves can be what?
Polarised
What can be said about the speed of electromagnetic waves?
All electromagnetic waves travel at the same speed, c, in a vacuum
What are electromagnetic waves?
Transverse waves with a range of wavelengths
In diffraction, when is the wavefront more curved?
When the wavelength is about the same size as the gap, and diffraction is at its greatest
A progressive wave carries what?
In what way?
It carries energy from one place to another without transferring any material
What are the wavelengths for gamma, X-ray, ultraviolet, infrared, micro and radio waves?
10^-12m, 10^-10m, 10^-8m, 10^-5m, 10^-2m, 1-1000m
What is phase difference?
The amount one wave lags behind another
What is displacement in terms of waves?
How far a point on the wave has moved from its undisturbed position
Which electromagnetic waves are more ionising?
Ones with a higher frequency and a shorter wavelength
Which electromagnetic waves are more ionising?
Ones with a higher frequency and a shorter wavelength
What is the difference between transverse and longitudinal waves?
Transverse waves- oscillations are at right angles to direction of propagation
Longitudinal waves- oscillations are in the same direction as the direction of propagation
In the first harmonic equation, what is mu the symbol for?
Mass per unit length
How many wavelengths are in the first harmonic?
1/2
How many wavelengths are in the second harmonic?
1
How many nodes and antinodes are there in the first harmonic?
2 nodes and 1 antinode
How many nodes and antinodes are there in the second harmonic?
3 nodes and two antinodes
In terms of waves, what does period mean?
The time taken for a whole cycle to complete, or to pass a given point
What do the wavelengths of visible light range from?
From 400nm for violet to 700nm for red
What is diffraction?
The spreading out of waves when they pass through an aperture or round an obstacle
Define antinode
A fixed point in a stationary wave pattern where the amplitude is a maximum
What is the principle of superposition?
If two waves are superposed, the resulting displacement at any point is the vector sum of the individual displacements.
What is phase?
A measurement of the position of a certain point along the wave cycle
What is frequency?
The number of cycles per second passing a given point
What is amplitude?
Maximum magnitude of displacement
What is a cycle?
One complete vibration of the wave
What is the value of c?
3.00 x 10^8 ms^-1
What do all the symbols mean in the equation: n x lamda = d x sin(theta)
n = order lamda = wavelength d = diffraction grating spacing theta = angle
What is the equation relating f and T?
f = 1/T
Intensity is proportional to what?
(Amplitude of wave motion)^2
What is wavelength?
The length of one whole wave cycle.
What is a wave?
The oscillation of particles or fields
What is the equation relating the speed of light, wavelength and frequency?
c = lamda x f
Why do optical fibres used for communications need to have cladding?
To keep signals secure To maintain quality It keeps light rays in It prevents scratching of the core Helps to prevent crossover of information to other fibres Provides strength for fibre
Why is a stationary wave formed on a string when plucked in the centre?
Progressive waves travel from the centre to the end and reflect .
These waves have the same frequency.
And the same/similar amplitudes
Superposition of the waves causes the stationary wave to be formed.
In Young’s Double Slit, if white light is used instead of red light, how does the appearance of the fringes differ?
Central bright fringe would be white
Side fringes are continuous spectra
Dark fringes would be closer together because the wavelength of red light is longer than the average wavelength of white light
The bring fringes would be blue on the side nearest the centre
The bright fringes would be wider.
How many degrees are there in one cycle of a wave?
360
What is the inside bit of an optical fibre called?
The core
What happens when light enters an optically denser medium?
It is refracted towards the normal.
Why does the core of an optical fibre need to be as narrow as possible?
To reduce multi path dispersion.
To prevent light loss from core.
How does multipath dispersion affect the light in optical fibres?
It cause light travelling at different angles to arrive at different times.
How does light loss from the core affect the signal from an optical fibre?
It causes the signal to get weaker.
What did Young’s double slit demonstration suggest about the nature of light?
That light was a wave rather than a particle.
What does monochromatic light mean?
Light of a single wavelength
What does coherent mean?
When waves have constant phase difference.
What are 5 examples of a transverse wave?
Electromagnetic radiation Surface of water in ripple tank Rope Slinky (when oscillated up and down like a transverse wave) Secondary waves
What happens when you direct light through two polarising filters that are at right angles to each other?
No light gets through.
Why are polarising filters used in sunglasses?
To reduce glare.
In the diffraction grating equation what is d?
The distance between the centres of two slits.
In single slit diffraction, how does making the slit narrower affect the fringes?
They have a lower intensity and are wider/have an increased separation.
In single slit diffraction, how do the side fringes compare to the central fringe?
They are narrower.
Why does material dispersion happen?
The refractive index of the optical fibre varies with frequency
Light consists of different frequencies which results in it travelling at different speeds in the fibre- this causes different wavelengths of light to reach the end of the fibre at different times.
What does material dispersion lead to?
Material pulse broadening.
How can material dispersion be reduced?
Use of monochromatic light so speed of pulse is constant.
How can multipath dispersion be reduced?
By using a monoxide fibre, which have a very narrow core, so that light is very nearly confined to one single path along the core.
When can total internal reflection happen?
When light goes from an optically more dense to an optically less dense material.
