3.1 Progressive And Stationary Waves Flashcards
Define frequency and give units
Number of waves passing a point per second
Hz (Hertz)
Define wavelength
The distance between 2 adjacent peaks/troughs on a wave
Define amplitude
Max. displacement of wave from equilibrium position
How can you find out time period of a wave using its frequency
T= 1/f
What’s phase difference and what’s it measured in
How much a wave lags behind another wave
Measured in radians, degrees or fraction of a cycle
What’s a longitudinal wave
Where oscillation of particles is parallel to direction of energy transfer
Rarefactions (low pressure areas)
Compressions (high pressure areas)
What’s a transverse wave
Waves where particle oscillations are perpendicular to direction of energy transfer
How fast do EM waves travel in a vacuum
3x10^8 m/s
True or False? Magnetic field and electric field in an EM wave are parallel to each other
False
Electric and magnetic field are at 90 to each other (perpendicular)
What does a polarising filter do
Only allows oscillations in one plane
How is polarisation used as evidence of nature of transverse waves
It can only occur if a waves oscillation are perpendicular to its direction of travel (as they are in transverse waves)
How’s polarisation used in antennas
TV and radio signals are usually plane-polarised by orientation of rods on transmitting aerial, so receiving aerial must be aligned in same plane of polarisation to receive signal at full strength
What’s a stationary wave
Wave which transfers no energy and whose positions of max. and min. amplitude are constant
What’s a node
Point on a stationary wave where the displacement is 0
What’s an antinode
Point on a stationary wave with max. displacement
What are conditions for a stationary wave to be produced
Waves must be of same frequency, wavelength and amplitude
Must be travelling in opposite directions
Conditions are often met when a wave is reflected back onto itself
How are stationary waves produced
When 2 progressive waves that are travelling in opposite directions in same plane superpose each other and have the same frequency, wavelength and amplitude
What’s constructive interference
Where waves meet in phase and so antinodes (regions of max. amplitude) form
What’s destructive interference
Where waves are completely out of phase and so nodes (regions of no displacement) form
Describe first harmonic for a stationary wave with 2 closed ends
Consists of 2 nodes at either end and an antinode in the middle
Describe second harmonic with one open end and one closed end
Consists of 2 nodes and 2 antinodes with one of the nodes at closed end and one antinode at open end
What’s a progressive wave
Transfers energy from one point to another without transfer of material
Diff between progressive and stationary
Progressive transfers energy and stationary doesn’t
