Waves 1 Flashcards
Progressive wave
A wave in which the peaks and troughs, or the compressions and rarefactions, move through the medium as energy is transferred e.g. P-waves (longitudinal seismic waves) and S-waves (transverse seismic waves)
Transverse wave
A wave in which the medium is displaced perpendicular to the direction of energy transfer - the oscillations of the medium particles are perpendicular to the direction of travel of the wave
Longitudinal wave
A wave in which the medium is displaced in the same line as the direction of energy transfer - oscillations of medium particles are parallel to the direction of the wave travel
Displacement
The distance from the equilibrium position in a particular direction - displacement is a vector so it has a positive or negative value
Amplitude
The maximum displacement from the equilibrium position (can be positive or negative)
Wavelength
The minimum distance between two points oscillating in phase, for example the distance from one peak to the next or from one compression to the next
Period
The time taken for one complete wavelength to pass a given point
OR the time taken for a particle to complete one cycle/oscillation
Phase difference
The difference between the displacements of particles along a wave, or the displacements of particles on different waves, measured in degrees or radians, with each complete cycle or a difference of one wavelength representing 360˚ or 2π (360˚ = in phase; 180˚ = antiphase; anything else = out of phase)
OR
How out of phase two points on a wave are
Frequency
The number of wavelengths passing a given point per unit time (f = 1/T)
OR number of cycles per second
Speed
The distance travelled by the wave per unit time (v=fλ)
Reflection
The change in direction of a wave at a boundary between two different media, so that the wave remains in the original medium
Refraction
The change in direction of a wave as it changes speed (due to a change in density) when it passes from one medium to another
Polarisation
The phenomenon in which oscillations of a transverse wave are limited to only one plane (plane polarised)
EM waves need special polarisers to be plane polarised if its electric field oscillates at random planes (unpolarised)
Diffraction
The phenomenon in which waves passing through a gap or around and obstacle spread out (most observed when gap is the size of the wavelength)
Total internal reflection
Reflection that occurs when:
- the light is travelling through the medium with the higher refractive index
- the incidence angle at the boundary is greater than the critical angle
Critical angle
The angle of incidence at the boundary between two media that will produce an angle of refraction of 90˚ (sinC = 1/n)
Electromagnetic wave
- Have oscillating electrical and magnetic components perpendicular to each other
- Travel at speed of light, c = 3x10^8, in a vacuum
- Don’t need a medium to propagate
- Transverse waves, so can be polarised
Gamma rays
Short-wavelength electromagnetic waves, with wavelengths from 10^-10m to 10^-16m
Infrared waves
Electromagnetic waves, with wavelengths from 10^-3m to 7x10^-7m
Intensity
The radiant power passing through a surface per unit area - unit Wm^-2
- I=P/SA, where SA can be a sphere (4πr^2), so I∝1/r^2
- I∝ A^2, where A decreases due to energy spreading out
Law of reflection
The angle of incidence is equal to the angle of reflection
Microwaves
Long-wavelength electromagnetic waves, with wavelengths from 10^-1m to 10^-3,
Radio waves
Long-wavelength electromagnetic waves, with wavelengths greater than 10^-1m
Visible light
Electromagnetic waves with wavelengths from 4x10^-7m to 7x10^-7m
X-rays
Short-wavelength electromagnetic waves with wavelengths from 10^-8m to 10^-13m, which can be used in medical imaging
Refractive index
Measure of the bending of a ray of light when passing from one medium into another (n=c/v)
Using an oscilloscope to determine wave frequency
The timebase (time interval represented by one horizontal square) for one wavelength gives the period
Using f=1/T, the frequency can be calculated with an oscilloscope (displays an electric signal in volts against a time trace)
Law of refraction
Snell’s law: n1sinθ1=n2sinθ2
Polarisation of light
First polaroid filter plane polarises light when held in front of the light source, then second filter when slowly rotated in front of the first filter, allows varying intensities of light, with the maximum and minimum intensities separated by a rotation of 90˚
- Malus’ Law: I = I0Cos^2θ
Polarisation of microwaves
Artificially produced microwaves are already plane polarised. Can place a metal grille in front of the microwave source, to investigate the intensity of microwaves detected by the receiver
Wave effects using a ripple tank
Wavelength - measure wavelength of ten ‘frozen’ waves using a metre ruler and divide by ten
Frequency - measure how long ten waves take to pass a point and divide by ten
Speed - calculate using wave equation
Refraction - slows down and wavelength shortens when wave enters shallower water
Investigating refraction using a transparent rectangular block
Draw around block and a normal line at the boundary between air and glass
Direct a thin slit of light from the ray box to the normal
Draw the direction of the ray as it enters the block and as it leaves the block
Connect the points of entry and exit
Use a protractor to measure the angle of incidence and angle of refraction
Investigate total internal reflection using a transparent semicircular block
Draw around block and a normal line at the centre of the boundary between glass and air
Direct a thin slit of light from the ray box to the normal, adjusting its direction until there is no light leaving the block i.e. the angle of refraction is 90˚
Use a protractor to measure the angle of incidence
Ultraviolet
Electromagnetic waves with wavelengths from 4x10^-7m to 10^-8m
