4.4 waves Flashcards
coherence
two waves with a constant phase relationship
amplitude
the maximum displacement of a wave from its rest position,
metres (m).
displacement (wave)
the distance moved by a particle from its rest position
electromagnetic wave
a self- spreading transverse wave that does not require a medium to travel through
first harmonic
in the fundamental mode of vibration, the length of the string is half the wavelength.
this produces the lowest possible frequency called the first harmonic
frequency, f
the number of oscillations passing a point per second
1/period
fundamental frequency
the lowest frequency in a harmonic series where a stationary wave forms
progressive wave
waves that transfers energy away from a source
longitudinal wave
vibrations are parallel to the direction of energy transfer
have the direction of oscillation of particles parallel to the direction of the wave.
transverse wave
vibrations are perpendicular to the direction of energy transfer
have the direction of oscillation of particles perpendicular to the direction of travel of the wave.
wavelength
the distance between two identical points on consecutive waves
(metres,m)
period
the time taken by the wave to complete one full oscillation
coherent sources
two waves have a constant phase difference
What do all EM waves have in common?
travel through a vacuum
possess both a magnetic wave and an electrical wave interlocked and at right angles to each other
travel at the speed of light
transverse waves
reflected, refracted and diffracted
demonstrate interference
be polarised
plane-polarised wave
oscillations of the field and the direction of travel are confined to a single plane
polarising filter
produces plane-polarised light by selective absorption of one component of the incident oscillations-
the filter transmits only the component of light polarised perpendicular to that direction
speed of a wave
frequency x wavelength
phase
a measure of how far through an oscillation a point is
phase difference
the proportion of a cycle by which two waves are out of synch
(radians)
wave speed
the rate at which a wave spreads through a medium
speed= wavelength/time perio
speed= frequency x wavelength
frequency formula
frequency = 1/period
wave speed formulas
wave speed = wavelength/period
wave speed= wavelength x frequency
reflection
angle of incidence= angle of refraction
when a wave rebounds from a barrier, changing direction but remaining in the same medium
refraction
the changing of direction of a wave as it enters a different medium due to a change in speed.
The light enters glass from air, the speed decreases which causes the direction to change.
diffraction
the spreading out of a wave when a it passes a gap or obstacle
occurs when the wavelength about the same size as the gap
As a wave passes a gap, the wave will spread outwards.
If there is a small gap, a more rounder wave is produced. (This is due to less point sources interfering).
radio waves
10^6 to 10^1
communication
Microwaves
10^-1 to 10^-3
Communication, cooking
Infrared
10^-3 to 700nm
Remotes, thermal imaging, heaters
Visible light
700nm to 400nm
Sight
Ultraviolet
400nm to 10^-8
Sun tanning, counterfeit detection
X-rays
10^-8 to 10^-13
Security, bone imaging
Gamma rays
10^-10 to 10^-16
Sterilisation, cancer treatment
common electromagnetic feature
All electromagnetic waves travel at c (speed of light), 3×10^8 ms^-1 through a vacuum.
differences and similarities between different regions of the electromagnetic spectrum
All travel at c (speed of light) through a vacuum
All consist of electric fields perpendicular to magnetic fields
All can be described as photons
They have different frequencies
They have different wavelengths
characteristics and dangers of UV-A, UV-B and UV-C radiations
UV-A has the longest wavelength of the UV region. The photons carry the least energy so pose the least danger, over exposure can lead to sunburns
UV-B has photons with higher energies which pose a higher risk and can cause skin cancer.
UV-C has the shortest wavelength and highest energy. However, the Ozone layer in the atmosphere prevents UV-C from penetrating.
role of sunscreen
used to absorb or reflect the UV radiation to prevent the radiation reaching the skin
stationary wave
formed whenever two progressive waves of same amplitude and wavelength travel in opposite directions and superimpose
difference between progressive and stationary waves
Progressive waves carry energy from one point to another
whereas a stationary wave is where this energy is stored within the wave rather than transmitted.
difference between progressive and stationary waves
Both progressive waves and stationary waves cause a displacement in the medium
Nodes
points on a stationary wave where there is no displacement of the particles at any time.
Antinodes
points on a stationary wave where there is maximum displacement at any time for the particles.
The distance between two adjacent nodes
λ/2
The distance between an adjacent node and antinode
λ/4
Fundamental mode of vibration
The lowest frequency in a harmonic series where the stationary wave forms.
Harmonics
Integer number of the fundamental frequency of a stationary wave.
total internal reflection
when light travels from a material of a higher refractive index to one of a lower refractive index
both refraction and a weak reflected ray occur
superposition
when two or more waves of the same type meet,
the resultant wave can be found by adding the displacements of the individual waves
they will overlap and interfere
constructive interference
when waves meet in phase
destructive interference
when waves arrive at a point completely out of phase
