Progressive and stationary waves Flashcards
displacement
distance and direction an oscillating particle moves from its rest position
metre (m)
amplitude A
maximum displacement an oscillating particle in the medium moves from its rest position
metre (m)
wavelength , lambda
distance between any point on a wave to an adjacent one that is exactly in phase with it
metre (m)
period T
time taken for one complete wave to pass a fixed point
second (s)
frequencyf
number of complete
waves passing a fixed point per second
hertz (Hz)
define the PHASE of a particle on a wave
the phase of a particle on a wave is the fraction of a cycle it has completed since the start of the cycle.
define the PHASE DIFFERENCE of two particles?
the phase difference of two particles on a wave, or on two waves is the fraction of a cycle by which their oscillations are separated.
what can phase difference be expressed in?
-fraction of the wavelength, lambda
-in degrees
-in radians
how many degrees and radians is 1 cycle?
1 cycle or 1 lambda = 360° = 2 π radians
if two points on a wave are separated by a horizontal distance, d ….. what’s is the phase difference in radians?
phase difference in radians= 2 πd/ wavelength
ONLY FOR PROGRESSIVE WAVES
what is a WAVEFRONT ?
a wavefront is a line or a surface on which the vibrations of the medium all have the same phase at all points.
how to convert between degrees and radians?
x 180/π
____>
π = 180
< ____
x π/180
how many degrees is 1 radian?
360° = 2 π radians
360°/ 2π = 1 radian
57.3° = 1 radian
how many radians is 90°?
π / 2
how many radians is 180°?
π
how many radians is 270° ?
3 π/ 2
how many radians is 360° ?
2 π
what are waves caused by?
Waves are caused by something oscillating the particles in the medium (or oscillating the field) through which the wave travels.
what is a PROGRESSIVE wave?
A progressive wave transfers energy from one place to another without transferring matter.
what equation are frequency and period related by
f= 1/T
what equation are the speed, frequency and wavelength of a wave related?
wave speed c = f x lambda
what are mechanical waves?
Mechanical waves require a physical substance to move through.
what are electromagnetic waves?
Electromagnetic waves can travel through a vacuum - they are oscillations in electric and magnetic fields that permeate space. All electromagnetic waves travel at the same speed in a vacuum:
3.00X109 m/s
what are longitudinal waves?
Longitudinal waves - oscillations of the medium are parallel to the direction of energy transfer. For example, sound waves.
what are transverse waves?
Transverse waves - oscillations of the medium are perpendicular to the direction of energy transfer. For example, electromagnetic waves and waves on a string.
what is the principle of superposition?
The principle of superposition states that when two waves meet, the total displacement at a point is equal to the sum of the individual displacements at that point.
what is reinforcement?
It two waves meet exactly in phase, they will add together CONSTRUCTIVELY to form a double height wave (reinforcement)
what is cancellation?
It two waves meet exactly out of phase (antiphase), they will add together DESTRUCTIVELY and cancel each other out
what is polarisation?
when the oscillation of a a transverse wave are restricted into a single plane, they are polarised.
if a wave can be polarised, it must be…
a transverse wave (longitudinal waves can’t be polarised)
how do transverse waves passing through a slit on a board become polarised?
only oscillations parallel to the slit pass through it
how are glares caused?
Light reflected from some surfaces (wate/ glan) is partially polarised. this reflected light causes glare.
how can glare be reduced?
by filtering out the polarised light using polarising filters
how is a stationary wave formed?
A stationary wave is formed when two progressive waves with the same frequency and amplitude, moving in opposite directions, superpose.
how are stationary waves most commonly formed?
Stationary waves are often the result of the reflection of a progressive wave superposing with the original wave.
what is a node?
A node is a point where there is no oscillation - the two waves always meet with a phase difference of 180° (pi radians).
what is antinode?
An antinode is a point where oscillation is at maximum amplitude - the two waves always meet in phase at that point.
distance between two nodes in a stationary wave is
distance between two node = 1/2 wavelength
what does it mean when all the point between two nosed oscillate in phase…
All the points between two nodes oscillate in phase, meaning they reach their maximum displacements at the same time.
do stationary waves that oscillate freely transfer energy to their surrounding?
Stationary waves that oscillate freely do not transfer energy to their surroundings. When stationary waves are formed:
• by sound waves, there is silence at the nodes and maximum volume at the antinodes
• in a microwave oven, there is no heating at the nodes, and maximum heating at the antinodes.
describe the first harmonic
The first harmonic:
As the frequency of oscillation is increased from zero, the first harmonic is seen at the lowest frequency that gives a pattern.
what equation is The frequency f of the first harmonic related to the length l, tension T, and mass per unit length u of the string by ?
f = 1/2 l square root (T/u)
describe the second and third harmonic….
The second harmonic occurs at twice the frequency of the first harmonic; the third harmonic occurs at three times the frequency of the first harmonic; etc.
what is the wavelength and frequency at the first harmonic?
wavelength= 2L (length of string)
frequency= f0
what is the wavelength and frequency at the second harmonic?
wavelength= L
frequency= 2f0
what is the wavelength and frequency at the third harmonic?
wavelength = 2L/3
frequency = 3f0
