4.2- Waves Flashcards
What is a wave?
The transfer of energy from one place to another without transferring any material
How can you tell the waves carry energy? (three-ways)
Electromagnetic waves cause things to heat up
X-rays and gamma rays can cause ionisation
Loud sound can make things vibrate
What is the definition of displacement?
How far are point on a wave have moved from its undisturbed position
What is the definition of amplitude?
The maximum magnitude of the displacement
What is the definition of wavelength?
The length of one whole wave cycle eg. crest to crest
What is the definition of a period of a wave?
The time taken for a whole cycle to complete
What is the definition of frequency?
The number of cycles per second passing a given point
What is a wave phase?
A measurement of the position of a certain point along the way cycle
What is the definition of phase difference?
The amount one way lags behind the other.
It is measured in degrees or radians
How do you measure wavelength on a longitudinal wave?
You measure compression to compression or rarefaction to rarefaction
What is the formula that links frequency and wave period?
F =1/P
What is the equation that links wave speed frequency and wavelength?
V=fλ
Tony is using an oscilloscope. He sees a wave on this oscilloscope. What is this displayed wave called?
A trace
What does an oscilloscope display?
Waves from a signal generator as a function of voltage over time
Gertrude is using an oscilloscope. She cannot read the time Dials clearly. Suggest how she could get an accurate measurement from her oscilloscope.
Gertrude could adjust the gain dial and the time base dial to make the wave easier to measure
How can you measure sound waves?
You can plug a microphone into an oscilloscope
What is a transverse waves?
A way that oscillate perpendicular to the direction of wave propagation
What is a longitudinal wave?
A wave that oscillate parallel to the direction of wave propagation
What are the two main ways of drawing transverse waves?
Displacement against distance
Displacement Against Time
How can we draw a longitudinal waves?
By plotting displacement Against Time
What is the definition of intensity?
The rate of flow of energy per unit area perpendicular to the direction of travel of the wave.
What are the units of intensity?
Wm^-2
What is the formula that links intensity power and area?
Intensity= Power/Area
What is the formula that links intensity and amplitude?
Intensity= amplitude^2
What properties do all the electromagnetic waves have in common?
They all travel at the same speed in a vacuum
They all carry energy
They can all be polarised
They can all be refracted, reflected and diffracted
Jenny is trying to create a polarizing filter for sound. Explain why this is impossible?
Polarisation can only happen for transverse waves sound is a longitudinal wave
What will happen if you have 2 polarising filters at right angles to each other?
No light will get through
What is plane polarisation?
Polarising a wave so that it only oscillates in One Direction
What is the definition of polarisation?
Restricting the oscillation of a transverse wave to One Direction
Can you polarise microwaves?
Yes, as they are a transverse wave
What do you use polarise microwaves? Why can’t you use polarising filters?
Do you use metal grills to polarised microwave because their wavelength is too long 4 polarising filters
What equipment would you need to investigate polarisation of microwaves?
A metal grill
A microwave transmitter transmitting polarised wave
Microwave receiver attached to a voltmeter
Rakesh is doing an experiment to polarised microwaves. His microwave receiver reads 0. Rakesh makes the assumption that is microwave transmitter is not working. Explain why Rakesh is wrong.
The grill could be aligned perfectly with the direction of the microwave and absorbs their energy
Explain how a metal grill can polarised microwaves?
The vibrating electric field of the microwave excites electrons in the metal grille
The energy of the incoming microwaves is absorbed and re emitted in all directions
Only a few of these remitter wave vibrating in the direction of the microwave receiver
Give two uses of polarising filters.
3D films use polarised light create depth
Polaroid sunglasses help prevent glare
What is the diffraction?
The way the waves spread out as they pass through a narrow gap or go around obstacles
What does diffraction depend on?
The size of the gap in comparison to the wavelength of the wave
What piece of equipment can you use to investigate diffraction?
A ripple tank
How can you demonstrate diffraction using a laser pointer?
You can shine it through a very narrow slit and observe how many dots are made
When do you get the most diffraction?
When the gap is the same size as the wavelength
What is the definition of reflection of a wave?
The wave is bounced back when it hits the boundary
When a wave reflects off a surface, the angle of incidence is always equal to…
The angle of refraction
What is the definition of refraction?
The bending of a wave as it passes through a different medium
A student says “ when a wave refracts it’s frequency must change “. Explain why the student is wrong.
The Frequency stays constant but the wavelength changes, which causes the wave speed to change
What is the definition of refractive index?
The ratio between the speed of light in a vacuum and the speed of light in that material
What is the formula for refractive index?
n=c/v
What is Snell’s Law?
n sinX = n sinX
If you had a glass block, how would you measure the refractive index accurately?
You could use a refractometer to measure the refractive index
What is the definition of the critical angle?
The angle of incidence when angle of refraction is 90 degrees
Why is refraction impossible at angles greater than the critical angle?
Because then total internal reflection will occur
Why are Critical angles important in life?
It allows optical fibre cables to work and diamonds to Sparkle
How does superposition occur?
2 or more waves interfere with each other and their displacements combine
What are the 2 types of wave interference?
Constructive interference
Destructive interference
2 identical waves interfere with each other. What kind of interference is this?
Constructive interference
2 waves with equal magnitudes of displacement in opposite direction interfere with each other. What type of interference is this?
Total destructive interference
A large wave interferes with a small wave with a negative displacement. What type of interference occurs?
Partial destructive interference
2 waves are in phase. What does this mean?
They are at the same point in the wave cycle.
They have the same displacement.
How many degrees and radians is 1 complete wave cycle?
360 degrees
2 pie radians
2 points on a wave have a phase difference of 180 degrees. What is their phase position?
exactly out of phase
What is the definition of 2 coherent sources?
2 sources with the same wavelength and frequency and a fixed phase difference between them
Tony can see a clear interference pattern. What does this mean about the sources of the wave?
They are coherent
Dillon measures a path difference of nλ. What kind of interference is occurring?
Constructive interference
Dillon measures a path difference of (n+1/2)λ. What kind of interference occurs?
Destructive interference
What is the definition of the principle of superposition?
When 2 waves cross, the resultant displacement equals the vector sum of the individual displacements
Frank sets up 2 speakers in a row playing the same sound and the walks past slowly. what will frank observe as he walks past?
Varying volumes of sound as constructive and destructive interference occurs in different places.
2 speakers are connected to an oscilator. Roger walks past and notices the sound is quiet in a certain area. What is the path difference in this area?
λ/2
Andrew is trying to prove that 2 water waves interfere with each other. How should she do this?
Hit a still lake with 2 dippers at the same time and watch the waves interfere with each other
What experiment do you need to do to prove that Light waves can interfere with each other?
Youngs double-slit experiment
What does monochromantic mean?
There is only 1 wavelength present
What is young’s double slit formula?
λ=ax/D λ=wavelength x=fringe spacing a=slit spacing d=distance from slits to screen
What dis youngs double slit experiment provide evidence for?
Light being a wave (able to diffract and interfere) and not tiny particle called corpuscles like newton suggested
Rodger shines a light through 600 slits. What will happen to his interference pattern compared to 1 slit?
His interference pattern will get sharper as there are more beams reinforcing the pattern. Brighter fringes become brighter and darker fringes become darker
How can you measure the wavelength of light using a diffraction grating?
By measuring fringe width and distance to the screen, you can work out the angle of the first order fringe.
Then, if you know the slit separation, you can find out the wavelength of the light
In youngs double slit experiment, How does wavelength affect fringe spacing?
A greater wavelength increases the fringe spacing so the pattern will spread out more
In youngs double slit experiment, How does Slit spacing affect fringe spacing?
if slit spacing is larger, the patterns will spread out less
How is a stationary wave created?
when a progressive wave reflects at a boundary and interferes with itself
What is the definition of a stationary wave?
The superposition of 2 progressive waves with the same wavelength moving in opposite directions
Is energy transmitted on a stationary wave?
nope
In a stationary wave, the pattern is normally jumbled. However, what happens at a resonant frequency?
the transducer produces an exact number of waves for the time it takes for a wave to be reflected. These waves then reinforce each other
