waves Flashcards
progressive wave is
example?
oscillation that travels through matter
all transfer energy, but not matter
sound
transverse waves? e.g.?
oscillations are perpendicular to the direction of energy transfer
em waves
longitudinal waves
example
oscillations are parallel to the direction of energy transfer
sound
amplitude definition
wavelength definition
maximum displacement from the equilibrium position
distance on a wave from peak to peak
frequency definition
the number of wavelengths passing a given point per unit time
when is a wave in phase/antiphase
in phase= particles oscillating perfectly in step with one another
antiphase= 180 degrees out of phase
reflection definition
law of reflection
when a wave changes direction at a boundary between two different media
angle of incidence = angle of reflection
refraction definition
where will it refract towards the normal?
when a wave changes direction as it changes speed (some reflection - partial reflection- will occur)
if it speeds up, it will refract towards the normal
what does refraction have an affect on
the wavelength but not its frequency
wave slows down - wavelength decreases
diffraction definition
diffraction occurs the most when?
when waves pass through a gap or travel round an object, they spread out
the size of the gap or obstacle is about the same as the wavelength of the wave
What is polarisation
The particles oscillate in one direction only- the wave is confined to a single plane
Which waves can be plane polarised
Transverse
Longitudinal cannot as oscillations already limited to one plane
What does partial polarised mean
When does this happen?
There are more waves oscillating in one particular plane but the wave is not completely plane polarised
When waves reflect off a surface
What is the intensity of a wave
UNITS
The radiant power passing through a surface per unit area
Wm-2
How to calculate intensity
Intensity and amplitude relationship
POWER / Cross sectional area
Intensity directly proportional to amplitude squared
order of the em spectrum (biggest wavelength to smallest wavelength)
Properties
1.Radiowaves 10’2low freq, high wavelength
2.Microwaves 10-2
3. Infra red 10-4
4. Visible light 400-700nm
5.Ultraviolet 10-8
6.X-rays 10-10
7. Gamma rays 10-12
High freq, low wavelength High E (dangerous)
properties of em waves
Can be reflected, rarefracted and diffracted.
Can be plane polarised.
Travel at the same speed through a vacuum
What is the relationship between rarefractive index and the normal
The higher the rarefactive index, the closer the refracted line to the normal
What is total internal reflection
When light strikes a boundary and all the light is reflected back into the original medium
What are the two condition required for total internal reflection
- Light must be travelling from a medium with a higher refractive index into a medium with a lower refractive index.
2.Angle that the light strikes the boundary must be above the critical angle
Angle of * at a * that produces
What is a critical angle
The angle of incidence at a boundary between two different media that will produce an angle of refraction of 90 degrees
what does superpose mean and principle of superposition
when waves overlap
When two waves meet at a point the resultant displacement at that point is equal to the sum of displacements of the individual points
difference between superposition and interference
interference is when the waves continuously pass through each other
difference between constructive and destructive interference
constructive is when the two waves are in phase
destructive is when the waves are in antiphase
coherence definition
waves emitted from two sources that have a constant phase difference
difference between path difference and phase difference
path difference to do with the distance travelled
phase distance to do with how out of sync the waves are - degrees
describe youngs double slit experiment
Used a monochromatic source of light and a narrow slit to diffract the light.
Light diffracting from the single slit reaches the double slit in phase, which then diffracts again
how is a stationary wave formed
when two progressive waves with same frequency and amplitude, moving in opposite directions superpose (which means overlap) to create nodes and antinodes which do not move
what is a node
a point on a wave with no displacement at all times
what is an antinode
point on a wave that oscillates with maximum amplitude
(in sound and microwaves)
where is the energy in stationary waves
SOUND- silence at nodes, maximum volume at antinodes
MICROWAVE - no heating at nodes maximum heating at antinodes
Fundamental wave (on a rope) properties
1st Harmonic
F0 frequency
Wavelength 2L
A
N. N
Fundamental wave (1 end open) properties
1st harmonic
F0 frequency
Wavelength 4L
A
N
How do the harmonics on a wave 1 end open differ from harmonics of wave on a rope
Harmonics wave on a rope increase by 1
Harmonica 1 end open only have odd harmonics
Fundamental wave (both ends open) properties
1st harmonic
F0
Wavelength 2L
A A
N
How to test polarisation
2 polarising filters one horizontal one vertical should have 0 intensity
Time period
time taken for one complete oscillation
Polarisation of microwaves practical
Place a metal grille in between a microwave receiver and a microwave transmitter. Slowly rotate the grille. Voltage across receiver will be ,maximum when the microwaves pass through the grille
