Chapter 11 Waves 1 Flashcards
What are primary and secondary waves?
They are both forms of progressive waves
What is an S-wave?
A secondary wave that is transverse
What is a P-wave?
A primary wave that is longitudinal
What is a progressive wave?
It is a wave that moves through matter or a vacuum and It transfers energy without transferring matter.
What is an equilibrium position in terms of waves?
It is the position that particles are in when there is no wave passing through it. Any deviation from this position is a deviation from the equilibrium
What is a restoring force?
This is the force that a particle experiences when it is restored back to its original position
What is a transverse wave?
It is a wave that oscillates perpendicular to the direction of travel of the wave.
What are some examples of transverse waves?(4)
Waves on the surface of water
Any electromagnetic wave
Waves on a stretched string
Swaves produced by earthquakes
What is a peak and what is a trough?
These are both the maximum displacement of a particle from equilibrium. Peak is the positive displacement and a trough is the negative displacement
What is a longitudinal wave?
It is a wave that oscillates parallel to the direction that the waves travel
What are some examples of longitudinal waves?(2)
Sound
pwaves from earthquakes
What is a compression and a rarefaction?
A compression is an area of high pressure and a rarefaction is an area of low pressure
What is displacement?
It is the distance that a particle is from equilibirum
What is amplitude?
It is the maximum displacement from equilibrium
What is wavelength?
This is the minimum distance between two identical points on a wave
What is the period of oscillation?
This is the time it takes for one oscillation
What is the frequency?
It is the number of wavelengths passing a point in a second, also the number of oscillations per second
What is wave speed?
It is the distance travelled by a wave per unit of time
What is the wave equation?
V = Fλ
What is the equation to find frequency from time period?
f = 1/t f = frequency t = timeperiod
What is phase difference?
it is Difference between the displacements of particles on a wave
What does in phase mean?
This is when particles are oscillating perfectly in step with each other. The reach there maximum displacements at the same time
What is the opposite of in phase and what does it mean?
Antiphase is when the particles are completely (180*) out of step and when one particle reaches it maximum positive displacement the other (equivalent) particle reaches its most negative displacement
What is a displacement-distance graph show?
It is a graph of the displacement per distance the wave has traveled. And it can also be interpreted as a snapshot of the wave. The wavelength can be calculated by measuring the distance between any two points on the graph
What is a displacement-time graph?
It shows the displacement of a particle on a wave as time varies. The frequency can be worked out by counting the number of waves per interval of time (second)
What is a reflection?
It is when a wave changes direction at a boundary between two different media whilst still remaining in the original medium
What is the law of reflection?
The angle of incidence is equal to the angle of reflection
How can light be represented?
It can be represented as a ray ( a straight line) or a wave front (perpendicular lines to the direction that the light moves)
What is refraction?
This is when light changes the medium it flows through and due to the change in speed it changes direction
What happens if the speed of the wave slows down when changing medium?
Refract towards the normal
What happens if the speed of the wave increases when changing medium?
It refracts away from the normal
What happens if a) light or b) sound enters a denser medium?
a) When light enters a denser medium it slows down
b) when sound enters a denser medium it speeds up
What happens when light enters water from air?
It bends towards the normal and the wavelength gets smaller
What is diffraction and what is the property unique to?
Diffraction is unique to waves and is when it spreads out as it passes through a gap
What is polarisation? and plane polarisation?
This is when particles oscillate in a single direction. along a single plane
What does unpolarised light look like?
It is light that oscillates in multiple directions.
What does the amount of diffraction rely on?
It relies on the size of the gap that it passes through and the wavelength
What does partial polarisation? and when does it happen?
This is when light oscillates in more than one plane but it not fully unpolarised. its sort of half way between
This happens when light reflects off a surface like a lake
What is intensity and what is its equation and units?
It is the radiant power passing through a surface per unit of area.
I = P / A
Units: Wm^-2
What is the equation for intensity from a sphere?
I = P / 4πr^2
What happens to the intensity if the distance from a source doubles?what is the general equation
The intensity is 1/4
I ∝ 1/r^2
How is amplitude and intensity related?
Intensity ∝ (amplitude)^2
What is special about electromagnetic waves vs other waves?
It does not need a medium to pass through
What is the order of the electromagnetic spectrum from large to small wavelength?
Radio wave Microwave Infrared Visible Ultraviolet Xray Gamma Ray
What is the wave equation for electromagnetic waves?
c = fλ
What is the speed of light? and symbol?
c = 3x10^8
What is a polarising filter and how does it work?
It is a filter that polarises light. It acts like a gate and so only the light that is oscillating with the direction of the rails is allowed through.
Light that oscillated differently is simply cut out
What is a use for polarising filters and explain how this is usefull?
It is used for ariels where the wave is polarised to reduce interference between different transmitters.
What is a refractive index?
This is a measure of how light bends when changing between mediums. Each medium is given a factor
What is the equation for the refractive index?
n = c / v n = refractive index factor c = speed of light in vacuum v = speed of light in the medium
What medium has a refractive index of 1?
A vacuum
What is the refraction law equation?
n1Sinθ1 = n2Sinθ2
n1 is the refractive index of medium 1 and θ1 is the angle of incidence against the normal
n2 is the refractive index of medium 2 and θ2 is the angle of incidence against the normal
What medium has the highest refractive index?
Diamond with an index of 2.42
What is total internal reflection?
This is when light leaving a medium is at such an angle that when it strikes the boundary and reflects instead of refracts
What are the two conditions of total internal reflection?
The light must be travelling from a medium of high refractive index towards one of low refractive index
The angle at which the light strikes the boundary must be above the critical angle
What is the critical angle?
This is the smallest angle that produces a total internal reflection. It is dependent on the medium involved
What is the equation for the critical angle?
Sinθ = 1 / n
n is the refractive index of the medium that the light is travelling through
How can the refractive index be calculated?
A ray box is used to put light into a semicircular box and then the angle of incident is change with the ray box until it totally internally reflects at an angle of 90* to the normal. The angle between the incident light from the ray box and the normal is calculated. Then the equation Sin θ = 1 / n is used
