Waves Flashcards
What is a progressive?
A progressive wave transfers energy without transferring material and is made up of particles of a medium oscillating.
Define frequency
Number of completed oscillations passing through a point per second
Define wavelength
The length of one whole oscillation
Define Phase
A position of a certain point on a wave cycle
Define Phase difference?
How much a particle lags behind another particle/wave
Define Period
Time taken to complete one full oscillation
State characteristics of two points that are in phase
- they’re at the same point of a wave cycle
- same displacement and velocity
- phase difference of a multiple of 2pi
- same frequency and same wavelength
- do not need the same amplitude
In terms of half cycles how do you determine if two waves are out of phase?
If they’re at odd integers of half cycles apart e.g 5 half cycles (one half cycle is pi)
Formula for wave speed (c)
speed = frequency * wavelength (c = f * lander)
Define transverse wave and give examples:
An oscillation of particles perpendicular to direction of energy transfer e.g all electromagnetic waves (radio waves, microwaves, light waves) , ripples in water, guitar strings etc
Define longitudinal waves and give examples:
- An oscillation of particles parallel to direction of energy transfer
- Made up of compressions and rarefractions that can’t travel in vacuums
e.g sound waves
What can transverse waves only do and what is its functions?
Can be polarised into one plane, which gives evidence to its perpendicular nature
- used in sunglasses to reduce glare or in TV signals where its strength is determined by the orientation of the rods.
What is superposition? and give me the two types.
When the displacements of two waves combine with each other as they pass:
Constructive interference - when 2 waves have displacement in the same direction
Destructive interference - when opposite displacements but equal in magnitude combine
How is a stationary wave formed?
From the superposition of two progressive waves, travelling in opposite directions in the same plane with the same frequency, wavelength and amplitude.
No energy is transferred in the stationary wave.
In a stationary wave what happens to points in the waves that meet completely out of phase and in phase?
- in phase, constructive interference occurs where antipodes are formed at maximum amplitudes.
- Completely out of phase, destructive interference occurs where nodes are formed at equilibrium.
Give an example of stationary waves?
Guitar strings and microwaves.
- a string fixed to one end where the wave travelling down due to the oscillator is reflected at the fixed end causing two progressive waves of the same wavelength, frequency and amplitude causing superposition so a stationary wave is formed.
What is the first harmonic and how can frequency be calculated?
It is the lowest frequency at which a stationary wave is formed, with two nodes and one antinode. The distance between adjacent nodes is half a wavelength.
f = 1/2L * Square root T/mass per unit length (in formula sheet)
Describe how stationary microwaves are formed
formed by reflecting microwave beams at a metal plate
you find nodes and antinodes using a microwave probe
Describe stationary sound waves:in a glass tube with sand
formed by placing speakers at one end of a closed glass tube where power lays across the tube.
It will be shaken at antinodes and settle at nodes.
How does increasing the wavelength change the pattern produced on the screen in diffraction?
- the central maxima would become wider
- the distance between central maxima and consecutive maxima become greater
how do convert 500 lines per mm into what you need for d
(1/500) *10^-3
DO NOT DO: (1/500*10^-3)
How do you work out max acceleration of a wave
- Use the max acceleration formula on the simple harmonic section
How does a pattern prove an electron has wave properties
- Diffraction and interference
- waves superpose to form bright and dark fringes when in phase
- Slit causes waves to spread out
How does a fluorescent screen show that electrons behave as particles
- electrons provide enough kinetic energy for instant excitation
- light emission due to excitation and de-excitation
- collision between incident electrons and moving electrons
How would the diffraction pattern of white light differ from red laser light
= central white bring
- all subsidiary maxima are of the spectrum
- less spaced out fringe
What has higher index core or cladding
core
If blue light has a greater refractive index which is faster blue or red light
Red light
What type of problem occurs due to red and blue light in a core
Red reaches before blue causing material pulse broadening
What is a progressive wave?`
When waves transfer energy from one point to another without transferring material
Can sound waves interfere
Yes, all waves must be able to diffract and interfere
