Waves Flashcards
Progressive Wave
A wave that transfers energy without transferring material. Made up of particles of a medium oscillating.
Amplitude
A wave’s maximum displacement from the equilibrium position.
Frequency
The number of complete oscillations passing through a point per second.
Wavelength
The length of one whole oscillation.
Speed
Distance travelled by the wave per unit time.
Phase
The position of a certain point on a wave cycle.
Phase difference
How much a particle/wave lags behind another particle/wave.
Period
Time taken for one full oscillation.
What does it mean when two waves are in phase?
They are both at the same point of the wave cycle. They will have the same displacement and velocity. Phase difference will be a multiple of 360 degrees.
What does it mean when two waves are out of phase?
When they’re an odd integer of half cycles apart.
Transverse waves
Oscillation of particles at right angles to the direction of energy transfer.
What kind of wave is a transverse wave?
All EM waves are trasverse and travel at 3x10^8 in a vacuum.
Longitudinal waves
Oscillation of particles is parallel to the direction of energy transfer.
Polarised
Wave that can only oscillate in only one plane.
What kind of wave can be polarised?
Only transverse waves.
Uses of polarisation
Sunglasses, reduce glare by blocking partially polarised light. TV and radio signals.
Superposition
Where the displacements of two waves are combined as they pass each other. The resultant displacement is the vector sum of each wave’s displacement.
Constructive interference
Occurs when two waves have displacement in the same direction.
Destructive interference
Occurs when one wave has positive displacement and the other has negative displacement, if the wave has equal but opposite displacements, total destructive interference occurs.
Stationary wave
Formed from the superposition of 2 progressive waves travelling in opposite directions with the same frequency, wavelength and amplitude.
Antinodes
Are formed when waves meet in phase, constructive interference occurs. They are regions of maximum amplitude.
Nodes
Waves are completely out of phase. Destructive interference occurs. Regions of no displacement.
First harmonic
Forms a stationary wave with two nodes and a single antinode. The distance between adjacent nodes is half the wavelength.
Stationary microwaves
Can be formed by reflecting a microwave beam at a metal plate, to find the nodes and antinodes use a microwave probe.
Stationary sound waves
Can be formed by placing a speaker at one end of a closed glass tube, lay powder across the bottom of the tube, it will be shaken at the antinodes and settle at the nodes. The distance between each node is half a wavelength, and the frequency of the signal generator to the speaker is known so by c=fλ the speed of sound in air can be found.
Path difference
The difference in the distance travelled by two waves.
Coherent
A light source that has the same frequency and wavelength and a fixed phase difference.
Monochromatic
Emit a single wavelength of light.
Diffraction
The spreading out of waves when they pass through or around a gap.
When does the greatest diffraction occur?
When the gap is the same size as the wavelength.
When do you get less diffraction?
When the gap is smaller than the wavelength. Most of the wavelenght is reflected. When it is larger there is less notable diffraction.
