waves Flashcards
Transverse Waves
A type of wave in which the particles oscillate at right angles to the direction the wave travels
Longitudinal Wave
A type of wave in which the particles oscillate parallel to the wave direction
wavelength / lambda
the distance between two matching points on neighbouring waves. in metres
amplitude
the maximum displacement a point moves from the centre of oscillation. in metres
amplitude in comparison to energy
the larger the amplitude, the greater the energy of the wave
Period
the time taken for a point on a wave to move through one complete oscillations. in seconds
Frequency
any wave is the number of oscillations per second measured in hertz
frequency equation
f = 1 / T
Mechanical waves
required a medium for transmission and are generated by vibrating sources
electromagnetic waves
are created when charged particles are accelerated. They require no medium for transmission
Maxwells conclusion
- maxwell found that the speed of the em waves would travel at a speed c = 1/ eu
- light must be an em wave as its same as his answer
- maxwell predicted that waves must also exist with frequencies much bigger and much smaller than light in a continuous spectrum
what did hertz demonstrate + discover
demonstrated - reflected, refracted and polarised
discovered - radio waves
Experiments with radio waves
- by placing a sheet of metal between the transmitter and detector he showed that radio waves are reflected by metal
he discovered that insulators do not absorb radio waves by placing his detector in another room
he strengthened his beam by placing a concave reflector around it
x-rays
had a wavelength of the order 10^-10
electrons emit x rays after high speed collisions or through a high energy transition in an atom
in space, x rays come from very hot stars of from charged particles accelerated to enormous speeds
x rays are produced by making high speed electrons collide with a metal target
EM Waves properties
1) travels at the speed of light
2)can be reflected, refracted and polarised
3)Show interference and diffraction effects
4) can travel through a vacuum
- Different frequencies interact with matter in very different ways
What is interference in physics?
Interference occurs when two or more waves meet and their amplitudes combine either constructively or destructively, resulting in changes in the overall wave pattern.
what is constructive interference?
when two waves are in phase and the amplitude increase when interfere
Destructive intefarance
180 degrees out of phase therefore trough is inligned with peak causing there to be no amplitude
What conditions are necessary for constructive interference?
Constructive interference occurs when waves meet in phase, meaning their peaks and troughs align, and their path differences are whole multiples of the wavelength.
What conditions are necessary for destructive interference?
Destructive interference occurs when waves meet out of phase, meaning their peaks align with troughs, and their path differences are odd multiples of half the wavelength.
What is phase difference?
Phase difference is a measure of how “in step” or out of step two waves are with each other. It’s usually measured in degrees or radians
How is phase difference represented mathematically?
Phase difference (ϕ) can be calculated using the formula: ϕ = (2π / λ) × path difference, where λ is the wavelength of the wave.
the principle of superposition
Where two or more waves meet, the total displacement at any point is the sum of the displacements that each individual wave would cause at that point
refraction definition
when light travels from one transparent material to another it changes direction . This happens because the light changes velocity
What happens when light goes from a less dense material to a more dense
The light slows down and bends towards the normal.
What happens when light goes from a more dense material to a less dense
The light speeds up and bends away from the normal.
What is Snell’s Law
sin i / sin r = 1n2 ( refractive index). It has no units.
also v1/v2 and lamba1/ lamba 2.
Wavelength changes as the wave moves from one material to another
definition of the absolute refractive index
The absolute refractive index of a material is the refractive index for light travelling from a vacuum into that material
what can 1n2 be shown as
n2/n1 = sin1 / sin2
which is rearranged into n1sin1=n2sin2
absolute index in terms of speed
c(speed of light in a vacuum) / Vs( speed of light in substance)
usage of stationary waves
detecting leakage in pipeline systems
x rays standing wave
for calibrating commercial and reference attenuators.
Definition of a node
A point along a standing wave with 0 amplitude
antinode
a point along the wave with maximum amplitude
What is the distance between a node and an antinode
a quater of a wavelength
Definition of a stationary wave
when two waves having equal amplitude and frequency moving in opposite direction along the same line. Waves formed by the reflected wave.
what is a harmonic
a stationary wave can only be produced at resonant frequencies, however there will be more than one for each length of string. These are called harmonics.
Difference between stationary and progressive waves
- each point along a progressive wave as equal amplitude, but for a stationary wave the amplitude varies
- adjacent points on progressive waves vibrate with different phase but all particles between nodes in stationary waves vibrate in phase
3.Energy is transferred through space in progressive waves but not in the case of stationary waves.
velocity of a wave in a string
v= root T/u (mass per unit length)
Equation for the fundamental frequency of a string
lamba =2l
f1= v/2l
General equation of a string
Fn= nv/2l
Fundamental frequency in a closed pipe
v=4 lamba
f1= v/4l
general equation for a stationary wave in a closed pipe
fn= nv/4l
what is an overtone
An overtone is any resonant frequency above the fundamental frequency of a sound.
Fundamental frequency in an open pipe
lamba = 2l
f1= v/2l
General equation for stationary waves in an open pipe
lamba = 2l
fn = nv/2l
state the equation used to calculate intensity
I = P/A Power/Area
What is the refractive index of a material through which light travels a speed of v?
n= c/v
where c is speed of light in vacuum
state the equation linking the refractive indexes and angles at an interface between two mediums
n1sino1= n2sino2
what is the critical angles
the angle of incidence which the angle of refraction is 90 degrees and all the light passes along the boundary between the mediums. Beyond this angle all light will be reflected
state the equation used to calculate a critical angle
sinc = 1/n
what is total internal reflection
total internal reflection is where all the light is reflected back at the boundary between two mediums. It occurs when light is incident at an angle greater than the criticle angle
what is the focal point of a converging lens
the single point where the parrallel rays of light entering the lens converge to
what is the focal length of a lens
the distance between the centre of the lens and the focal point
what is the equation used to calculate the power of a lens
power = 1/ focal length
How do you calculate the total power of a combination of thin lens
p = p1 + P2 + ..
what is a real image
a real image is one that can be projected onto a screen and is always inverted. real images are the consequence of light meeting at a focal point.
what is a virtual image
virtual images are the consequence of rays of light appearing to meet a point. they cannot be projected onto a screen.
state the equation used to calculate the magnification of an image
magnification = image height / object height
What is plane polarisation?
Plane polarisation is when the oscillations of a wave are restricted to a single plane
