Waves Flashcards
Wavelength - Radio waves
10^6 - 10^-1
Wavelength - Microwaves
10^-1 - 10^-3
Wavelength - Infrared
10^-3 - 7x10^-7
Wavelength - visible
7x10^-7 - 4x10^-7
Wavelength - ultraviolet
4x10^-7 - 10^-8
Wavelength - X rays
10^-8 - 10^-13
Wavelength - gamma rays
10^-10 - 10^-16
Mechanical waves
regular vibration of particles
Electromagnetic waves
oscillating electric and magnetic fields - they do not need particles so can pass through vacuum
Longitudinal waves
displacement of particles is parallel to the direction of propagation of the wave’s energy
Transverse waves
displacement of particles is perpendicular to the direction of propagation of the wave’s energy
Progressive waves
transfer energy from one place to another
Wavelength
distance from any point on the wave to the consecutive point that are in phase
Displacement
distance of the point on the wave from its equilibrium position
Amplitude
maximum displacement of a point on the wave from its equilibrium position
Wave
a series of regular oscillations which transfer energy through matter or space
Intensity of a wave
Rate of energy transmitted per unit area normal to wave velocity
How does intensity of a wave decrease as it travels through space?
The waves spread out, some of the wave may be scattered or absorbed
Phase difference
the fraction of one whole cycle between the vibrations
Doppler effect
the apparent change in frequency (or wavelength) of a wave when the source is moving relative to the observer
principle of superposition of waves
When two waves of the same type meet, they combine together. The total displacement of the resulting wave is the vector sum of the displacements of the individual waves at that point in space.
Nodes
the points on the wave that do not move
Antinodes
the points on the wave that oscillates with maximum amplitude
Explain the formation of antinodes
when two waves arrive at the same point IN PHASE. The two waves superimpose CONSTRUCTIVELY so their two displacements add together to give maximum displacement (constructive interference)
Explain the formation of nodes
when two waves arrive at the same point IN ANTIPHASE. The two waves superimpose DESTRUCTIVELY so their two displacements add together to give ZERO displacement (destructive interference)
wave speed of progressive wave
speed at which energy is transferred
period
time taken for one complete oscillation to pass a point
frequency
number of oscillation per unit time of the source
wave speed of a stationary wave
rate of transfer of energy of the wave fronts of the two progressive waves that superpose to create the stationary wave.
condition for stationary wave to form
- two progressive waves of the same frequency, same type and similar amplitude
- travelling in opposite directions
- overlap so that superposition takes place
how to use CRO
- adjust the time base to get approx. 2 waves on screen
- count the number of divisions for one complete wave
- multiply the number of division by time base setting to get the time
- use equation F=1/T to find the frequency
differences between progressive and stationary waves
- progressive waves do not have nodes or antinodes, stationary waves do
- on progressive waves, two consecutive points are not in phase, on stationary waves, they are in phase
similarities between progressive and stationary waves
air particles vibrate parallel to the direction of wave travel
Suggest how stationary electromagnetic waves might be set up
A microwave transmitter is placed a distance from a metal plate that reflects the emitted waves.
When the position of the transmitter is adjusted to achieve a suitable resonant length between transmitter and reflector, stationary waves would be formed by the superposition of the emitted and reflected waves.
path difference between two constructive waves
nλ
path difference between two destructive waves
(n+1/2) λ
what is meant by the term ‘coherence’
- two waves of same type
- constant phase difference
- overlap
How coherent source is produced?
same source diffracted by double slit
What is observed on screen by double slit?
- bright and dark fringes
How to diffract a white light source?
use a coloured filter then pass through single slit, then double slit
How can fringes be seen more clearly?
- screen is moved further away
- room is dark
- slits are very close together
monochromatic
light of a single wavelength / frequency
How the wavelength can be found using young’s double slit (equation)
λ = ax/D
How to measure λ accurately in Young’s double slit?
large D to give greater fringe spacing. Measure across several fringes, repeat for different distances. Could plot a graph of X v D and find gradient.
What is a diffraction grating?
A large number of equally spaced lines ruled on a glass or plastic slide
What precautions you should take when calculating a value for wavelength using laser?
- protective goggles
- not looking directly into laser
- avoid reflections (shiny surfaces, jewellery)
Explain the term interference (same for principle of superposition)
when two waves meet, the resultant displacement is the sum of individual displacement
Dispersion
The splitting of wave into different wavelengths
