Ch.4 WAVES Flashcards
what’s a transverse wave
a type of wave that vibrates perpendicular to the direction of energy transfer
what are longitudinal waves
they’re waves that vibrate parallel to the direction of energy transfer
these consist of compressions and rarefractions in the medium
how can light be blocked using polarising filters
when they are right angle to eachother
and it could be partially polarised when it’s in a 127 degree angle
explain how polarisation happens in tv signals
tv signals are polarised by the orientation of the rods on the broadcasting aerial
to receive a strong signal, the rods on the receiving aerial should line up with the rods of the transmitting aerial
if not align than signal strength will be lower
why can’t sound waves be polarised
because they are longitudinal waves so they don’t polarise and the vibrations move with the energy transfer these consist
what’s the principle of superposition
when two or more waves cross, the resultant displacement equals the vector sum of the individual displacement
what are the two interferences and what do they do
CONSTRUCTIVE :
when a crest and a crest meet to give a bigger crest or trough to trough
DESTRUCTIVE :
when crest and trust meet to make smaller amplitude
how are points in phase or out of phase
when two points phase difference is zero or 360 or a multiple of 360 they’re in phase
when two points phase difference is an odd number multiples of 180 or pi than they’re exactly out of phase
what is coherent
when sources have the same wavelength, same frequency, and a fixed phase difference between them
how can u get constructive and destructive interference based on path difference
Constructive :
if an equal distance from two sources that are coherent and in phase it will give constructive interference
also if the path difference is a whole number of wavelengths
Destructive :
points where path difference is half a wavelength or one and a half wavelength, etc. the waves arrive out of phase and you’d get destructive interference
what is a stationary wave
it’s the superposition of two progressive waves with the same frequency moving in opposite directions
no energy is transferred by it
what are nodes and antinodes
node is when the he vibration is at zero
and anti ode is when vibration is at max amplitude
how does the stationary wave form
when the oscillator produces an exact number of waves in the time it takes for a wave to get to the end and back again, then the original and reflected waves reinforce eachother
how much is the wavelength if the length of string is 2m and and first harmonic freq is 30hz
stationary wave
the length of the string for stationary wave at fundamental freq is half the wavelength of the wave so 2x2=4
how does the variation of amplitudes along the string differ from that of a progressive wave
when string format standing wave it’s amplitude varied from a max at the antinodes to zero at the nodes while in progressive waves all the points vibrate at the same amplitude
