Mod 4: Waves Flashcards
Define the term progressive wave
A wave which transfers energy from one place to another with a wave front which travels through the material
What is a longitudinal wave
Waves which the particles oscillate parallel to the energy propagation. They have refractions (areas of low pressure0 and compressions ( areas of high pressure)
What is the question for frequency
F= 1/t
What is the phase difference of a wave and what is it measured in
The amount of wave lags behind another as a proportion of the wavelength.
It is measured in radian
When Can waves be reflected and refracted at the same time
At low angles of incidence, most of the waves will be refracted however some will reflect
When is the most diffraction seen
When the gap and wavelength are the same size
What will happen to wave if the gap is much bigger than the wavelength of the waves
The waves will mostly be reflected however some will be diffracted
Can all waves be polarised
Only transverse waves
What is the difference between polarised and unpolarised waves
Polarised waves only contains waves oscillating along one axis.
Unpolarised waves can be oscillating in any direction perpendicular to the axis of propagation
How can a ripple tank be used to investigate diffraction
Create waves in the tank
Vary the size of a gap for the waves to pass through
Note how the direction of the waves [passing through the gap changes
What is a progressive wave
A progressive wave carries energy from one place to another without transferring any material. the transfer of energy is in the same direction as the wave is travelling 
What do x-rays and gamma do?
They knock electrons out of their orbits, causing ionisation
Define displacement in the terms of waves
How far apart on the wave has moved from it, undisturbed position
Define wavelength
 the length of one whole wave cycle
Define period
The time taken for a whole cycle to complete
Define frequency
The number of cycles per second passing through a given point
Define a phase
A measurement of the position of a certain point along the wave cycle
Define phase difference
The amount one wave lags behind another
What is a phase and the difference measured in?
They are measured in angles in degrees or radians
What does a cathode ray oscilloscope measure?
Voltage
What does a cathode ray oscilloscope display on its screen?
Display waves generated from a signal generator as a function of voltage overtime
What is the displayed wave called on an oscilloscope?
A trace
What is the vertical axis on the oscilloscope and what is it controlled by?
The vertical access is the volt and it is controlled by the gain dial
What is the horizontal axis of an oscilloscope?
It is the seconds / timebase
What are the units for amplitude?
Metres 
What dials can you alter to make an oscilloscope wave trace easier to measure?
The base and the gain dial
Name some examples of transverse waves
Electromagnetic waves
Ripples on water
Waves on strings
 light waves
Define intensity , in terms of waves. And give the equation.
 intensity is the rate of flow of energy per unit area at right angles to the direction of travel of the wave
I=P/A
mEnsured in wm^-2
What is intensity proportional to?
Intensity is proportional to amplitude, squared
Why is intensity, proportional to amplitude? Squared
Intensity is proportional to energy, and the energy of a wave depends on the square of the amplitude
Give two similarities of EMM waves
They can all travel in a vacuum, and they all have a speed of 3× 10 to the power of, eight
What do EMM waves consist of?
Waves consist of vibrating electric and magnetic fields which are at right angles to each other in the direction of travel
 what is energy directly proportional to?
Energy is directly proportional to the frequency
What is the wavelength of radio waves what is the penetration and what is the uses?
Wavelength equals 10 ^-1 - 10^6
Penetration- passes through matter
The uses are radio transmissions 
What is the wavelength penetration and uses of microwaves?
Wavelength = 10^-3 - 10^-1
Penetration is it mostly passes through matter however, it can cause some heating
The uses are for the radar microwave, cooking, and TV transmissions 
What is the wavelength penetration and uses of infrared radiation?
Wavelength = 7 x 10^-7. - 7 x 10^-3
Penetration is that it is mostly absorbed by matter, causing the matter to heat up
The uses are for heat, detectors, night, vision, cameras, remote, control, and optical fires 
What are the wavelength penetration and uses of visible light?
Wavelength = 4 x 10^-7 - 7 x 10^-7
Penetration is that is absorbed by matter, causing some heating
It’s uses as human site and optical fibbers 
What are the wavelength of penetration and uses of ultraviolet light?
Wavelength = 10^-8 - 4*10^-7
Penetration is that it is absorbed by matter and has a slight ionisation
It is used for sunbeds and security marks that show up under UV

What is the penetration and uses of x-rays?
The penetration is that it mostly passes through matter, but causes ionisation as they pass
They are used to see damage to bones and teeth. They are using airport, security scanners and to kill cancer cells.
What is a penetration and uses for gamma rays
The penetration is that they mostly passed through matter, but cause ionisation as they pass
The uses are for the irradiation of food, sterilisation of medical instruments, and to kill cancer cells
Define plane polarisation
Polarising a wave so that it’s only oscillates in One Direction
What does a polarising filter do?
They only transmits vibrations in one direction
How can you arrange polarising filters, so that no light can pass through
By placing two polarising filters at right angles to each other
How can you prove if a wave is transverse or long tunnel?
You can check if the wave can be polarised as only transverse waves can be polarised
Define wave speed
The distance travelled by the wave per unit time
Define an unpolarised wave
Transverse waves with oscillations in many direction, which are all perpendicular to the direction of energy transfer
Define a plain polarised wave
A transverse wave with oscillations in One Direction, which is always perpendicular to the direction of energy transfer
How can you design an experiment to investigate the polarisation of light using two polarising filters
 align the transmission axes of two polarising filters, so they are both vertical. Then shine unpolarised the light on the first filter.. keep the first filter position fixed and rotate the second filter.
As you rotate the second filter, the amount of light that can pass through will vary, and when the filters are perpendicular to each other, no lights will be able to pass through .
Explain how you can use two polarising filters to vary delight that is able to pass through
When both the polarising filters are aligned, all of the light can pass through the first, and the second, however, as you rotate the second filter, the amount of lights that can pass through wheel vary.
Of the component of the rotating filter, the more vertically polarised light can pass through .
 This means the intensity of the light getting through the second filter will gradually decrease as you shy away from the vertical components.
What happens if the two transmission axes of two polarising filters are at 45° to each other
The intensity will be half in the second filter than the first filter
Name some examples of polarising filters
3-D. Films
Polaroid sunglasses
Why do polarising filters not work on microwaves?
Because that wavelength is too long
What is used instead of polarising filters on microwaves?
Metal grills
Describe an experiment used to polarise microwaves
Place a metal grille in between a microwave, transmitter and the receiver attached to a voltmeter
The microwave transmitter will always transmit vertically, polarised microwaves therefore, you will only need one metal grille
Then turn on the microwave transmitter and read the signal on the voltmeter
In the polarisation of microwaves experiment, when will the intensity of the microwaves passing through the grille be at a maximum
When the direction of the vibrations of the microwaves and the wires on the grille
Perpendicular to each other, therefore the grille will need to be placed horizontally as microwave, transmitters, always transmit, vertically, polarised waves
In the polarisation of microwaves experiment, when will there be no signal of microwaves?
When the wires of the metals grille are aligned with the direction of the polarised waves
What happens to the intensity of the polarised microwaves when you rotate the grille
As you rotate the grille the intensity of the polarised microwaves able to pass through it decreases therefore the reading on the volt meter decreases
Why does the intensity of the microwave drop to 0, when the wires of the grille are aligned with the direction of microwaves
Because the grille Is absorbing their energy
Explain how the grille absorbs the energy of the microwaves in the polarisation of microwaves experiment
The vibrating electric field of the microwaves will excite the electrons in the metal grille
The energy of the incoming microwaves are absorbed and remitted in all directions
However, only a few of those remitted waves are vibrating in the direction of the microwave, receiver as the microwave receiver, only receives microwaves in one plane
However, when the wires and vibrations of the waves are aligned, more electrons are excited, therefore this causes a drop in intensity .
Define diffraction
The spreading out of waves as they pass through a gap or around an obstacle
What does the amount of diffraction depend upon?
It depends on the size of the gap in comparison to the wavelength of the wave
What are ripple tanks?
Ripple tanks are shallow tanks of water that you can generate a wave in
How are waves created in a ripple tank and what do the wave fronts look like
This is done by an oscillating paddle, which continually dips into the water and creates regular waves with straight parallel wave fronts
When do you get the most diffraction
When the gap is the same as the size of the wavelength
When are water waves reflected back on themselves instead of diffracting
When the size of the gap becomes too small and the water waves cannot pass through it anymore
Describe the waves when moving around an obstacle
When a wave meets an obstacle, you get defraction around the edges however, behind the obstacle will be a shadow where the wave is blocked
The wider the obstacle compared to the wavelength of the wave, the less diffraction you get therefore a longer shadow
Define reflection
When a wave bounces back when it hits a boundary,
What is the angle of incidents equal to when a wave is reflected
The angle of incident is always equal to the angle of reflection
How can you set up an experiment to show that waves can be reflected?
Set up a ripple tank so that the oscillating paddle is creating regular waves with straight parallel wave fronts
Then place a barrier in the tank at an angle to the wave fronts
The angle of the incoming waves that are made with the normal to the barrier are called the angle of incidents . Normal is perpendicular to the barrier .
You should be able to see the waves reflecting of the barrier and travelling in a different direction to the way they arrived
The angle between the direction of the reflected waves and the normal to the barrier is called the angle of reflection
You can then change the angle of incident to see the angle of reflection 
Define refraction
The change in direction of a wave when it changes speed as it passes from one medium to another
How can you tell if a wave is slowing down from observations
If the ray bends towards the normal, it is slowing down, and the rays is growing from a less optically, dense material to a more optically dense material
Why does the speed change when entering a different optical dense material?
Because the wavelength of the wave is changing, and the frequency stays constant speed is directly proportional to the wavelength
How can you use a box and a glass block to investigate refraction
Place a glass block on a piece of paper and draw around it
Use the ray box to shine a beam of light into the glass block and turn off any other lights in the room
Trace of the incoming and outgoing, beams of the light on either side of the block
Then remove the block and join up the tooth path with a straight line
From the diagram, you should be able to see how the path of the ray bent when entering and leaving the block
Measure the angles of incident and refraction, where the light enters and exit the block
Describe the pathway of the ray of light in the box and glass block experiment when entering and exiting the glass block
There is less optically dense than the glass therefore, as the light enters the glass block, it will bend towards the normal, and the angle of incident would be greater than the angle of refraction as it slows down however, when exits the block it will bend away from the normal, and the angle of refraction will be greater than the angle of incident as it is speeding up.
When does light travel the fastest?
When it is in a vacuum
Why does light not travel as fast in other materials than when it travels in a vacuum?
Because it interacts with particles in the materials
What is the absolute refractive index?
The ratio between the speed of light in a vacuum and the speed of light in a material
Give the equation for the absolute refractive index and explain, explain what they are
Absolute refractive index(n) = speed of light in a vacuum(c) / speed of light in that material (v)
The speed of light in a Vacuum(c) always equals 3×10 to the power of eight
When the refractive index of air is not given, what do you assume it is?
1
Give the equation from snell’s don’t law
N1 x sin theta1 = n2 sin theta2
Where N1 is the refractive index of the first material and theta one is the angle of incident
And N2 is the refractive index of the second material, and theta two is the angle of refraction
What device can you use to act accurately, measure the refractive index of a material and how can you use it?
A refractometer will shine a beam of light. At the sample you can then view the refracted beam through a microscope to measure its angle of refraction.
Define total internal reflection
All of the waves reflect when they meet a boundary between two media
What is the critical angle C and why does it happen?
This is the angle for which the angle of refraction equals 90° and the light is reflected along the boundary.  this happens when you increase the angle of incident and the angle of refractions gets closer and closer to 90°.
Give the equation from snails law for light, hitting a material to air boundary
Sin C (critical angle) = 1/n (refractive index)
When does total internal reflection happen?
When the angle of incident is greater than the critical angle
Describe an experiment to investigate critical angles and total internal reflection
Shine a light ray into the curved surface of a semi circular glass block so that the light always enters at right angles to the edge. This is so that the ray won’t refract as it enters the block and only when it leaves from the straight edge.
Then vary the angle of incidents until the light beam refracts so much, so that it exits the block at a straight edge in which you have found the critical angle sea
When the angle of incident is greater than the critical angle, total internal reflection will be reached
Define the critical angle C
The angle of incident, which gives an angle of refraction of 90°
What is the refractive index of glass
1.52
What is the refractive index of a vacuum?
1
What is the refractive index of water?
1.33
What is the refractive index of a diamond?
2.42
An exploding star in a distant galaxy omitted. A burst of electromagnetic radiation, x-rays and ultraviolet radiation from this burst were detected simultaneously at earth. Why were these waves detected simultaneously?
Because they both travel at the same speed
In an experiment using microwaves a metal grille consisting of a series of long metal rods is placed between a transmitter and a detector. The grille is slowly rotated through 180° about about the line, the detective signals at the varies from 0 to maximum and back to 0 again, explain why this happens
Microwaves are polarised from the transmitter. At 0° or 180° The grille block the waves and at 90° the grille allows all the microwaves to pass
How can you demonstrate that reflected light is plain polarised?
Use a polarising filter, and as you rotate the filter, the intensity will change, therefore light can be plain polarised
You are provided with a Ray box, a semi circular block of plastic and other normal laboratory equipment, describe how you could measure the refractive index of the block, using the critical angle method.
Increase the angle of incidents until the rate of light runs along the boundary of the semicircular block. Then use this angle to determine N using the equation.
N=1/sin C
Light travels from air to water. The refractive index of water is greater than the refractive index of air, compare the speed, frequency and wavelength of light in air and in water.
Speed of light decreases in water, as it is more optically dense
Frequency always remains constant therefore, it’s the same in both water and air
Wavelength is now smaller in water as wavelength and wave speed are directly proportional
Describe how you can use a box and a rectangular block of plastic to accurately determine the refractive index of the plastic block
Place the plastic block on paper and trace around it, then shine a light ray and trace, the pathway of the light, the incoming and outgoing light rays. Then connect these paths with a straight line and measure the angle of incident and refractions relative to the normal using a protractor, then used
n= sin theta i / sin theta r
Describe and explain how you could demonstrate the diffraction of soundwaves in a laboratory
Use a loudspeaker and a slit such as a doorway
Then switch on the loudspeaker
The sounds should spread from the slit
Then compare the size of the slit to the wavelength of the
Explain why longitudinal ways cannot be polarised but transverse waves can
Longitudinal waves only oscillate in one direction, which is parallel to propagation, however, the transverse waves oscillate in any direction. Therefore, you can polarise them to only oscillate in One Direction.
A child removes the plastic lenses from 3-D glasses. She holds one lens in front of the other with the transmission axis perpendicular to each other. She then proceeds to rotate one of the lenses through 90° describe what the child observes when light is passed through.
Initially no light can transmit through both of the lenses as their transmission axis is perpendicular to each other however, as the lens is rotated, an increasing amount of light can flow through, and when the axis align at 90°, all of the lights can flow through
What is the wavelength of radio waves?
10^-1 to 10^6
What is the wavelength of microwaves?
10^-1 to 10^-3
What is the wavelength of infrared radiation?
10^-3 to 7x10^-7
What is the wavelength of visible light?
7x10^-7 to 10 to 4x10^-7
What is the wavelength of ultraviolet light?
4x10^-7 to 10^-8
What is the wavelength of x-rays?
10^-8 to 10^-13
Define path difference
A measure of how far ahead a wave is compared to another wave, which is usually expressed in terms of wavelength
If particles are oscillating in step with each other ( they are a whole wave cycle away from wachother)what are they?
They are in phase and their phase fdifference will usually be a multiple of two pi or 360°
When particles are oscillating out of phase, what equation can be used to calculate the phase difference?
X divided by lambda multiplied by two pi.
Where X is the separation in wavelength between the two particles?
Describe the distance between two particles when they are in anti-phase
When two particles are oscillating with the phase difference of pi. and half a wavelength out of step with each other, they are said to be in anti-phase.
At what phase difference will two points on a wave be completely out of phase
When they are half a wavelength apart, so the phase difference is pi radians, this is called anti-phase
What is the principle of superposition?
The principal states that when two or more waves cross the resultant displacement equals the vector sum of the individual displacement
What is interference?
When you are more waves, suppose with each other this effect is called interference
What happens when a crest meets another crest and when a trough meets another trough and what are these expense examples of?
When a crest of a wave meets another crest, this gives the resultant crest, which is the sum of the two amplitude of the two crusts
This is the same for troughs
These are both examples of constructive interference
What happens when a crest and a trough of equal size are superposed with each other and what is this called?
When when a crest of a wave and a trough of another wave, meet the two displacement of the waves, cancel each other out completely, this is called destructive interference
What should the condition be so that the interference of two waves or more should be noticeable
The waves must have similar amplitudes, which are nearly equal meaning the the sources of the waves must be coherent
What is meant when two points on a wave are in phase
This means they are both at the same point in the wave cycles, and they had the same displacement and velocity
What can we say about two points with a phase difference of zero or a multiple of 360°?
We can say that these two points are in phase
What can we say about points with the phase difference of the odd number multiples of 180°?
We can say that these points are exactly out of phase
Describe what is meant by coherent
Two sources are coherent if they have the same wavelength and frequency and a fixed phase difference between them
When do you get constructive interference?
When both sources are an equal distance from each other at any point
And when the path difference is a whole number of wavelength
What is the equation for path difference when constructive interference occurs
Path difference = n x wavelength. N is an integer 
What is the equation for past difference when destructive interference occurs
Path diff = (n+ 1/2) x wavelength
How can you observe the interference with soundwaves?
Connect to speakers to the same oscillator, so they are coherent, then place them in line with each other
Walk slowly across the room in front of them and you will hear varying volumes of sound at the point where the sound is the loudest. The past difference is a whole wavelength or 0 paths difference in the middle , and when the sound is the quietest is at the point where the path different is an odd number of half wavelength.
Why is it important to correctly align the aerial of a TV in order to receive the strongest signal
The waves are polarised
So aerial must be aligned with the plane of polarisation of the wave
Define intensity of a wave
The power per m^2
An investigation of a single loudspeaker was positioned behind a wall with a narrow gap, this was to investigate refraction. The reading on the oscilloscope was a wave with a short wavelength and a high amplitude, the experiment was done again with the sound waves at the same amplitude but a higher frequency. Explain how the wave would look
As the amplitudes the same however the frequency has increased. This means the particles will have to travel a further displacement in a shorter amount of time. This means the wave speed would be smaller and as wave speed is proportional to wavelength ,The wavelength of the sound wave would also be smaller
The peak would have a smaller spread however the same energy is concentrated over a smaller area therefore the peak would be higher
Explain how total internal reflection is used to transmit information along an optical fibre
An optic fibre has cladding on the outside and a core in the middle, the cladding has a refractive index less than the core, therfore the angle of incidence is greater than the critical angle so total internal reflection happens repeatedly.
State one application, other than in education of a polarising filter and give a reason for it to use
They are used in sunglasses to reduce glare
Explain why total internal reflection will not occur when the ray travels from water to glass. Water has a lower refractive index and glass.
Total internal reflection only occurs when a ray travels from a higher refractive index to a lower refractive index
