waves Flashcards
what do waves do
transfer energy without transferring matter
what is a progressive wave
a wave which carries energy from one place to another
how can you make a wave
having a particle or a field oscillate
what happens to the source of a wave as the wave moves
the source of the wave loses energy as the wave transfers the energy
how can you tell a wave carries energy?
things heat up, ionisation occurs, you can hear sounds
what is refraction
when a wave changes speed and direction as it moves from one medium into a different medium
what is reflection
when a wave bounces back
what causes the change in direction during refraction
as the speed of the wave slows down when it hits another medium at an angle.wave hits the medium at an angle one part of the wave slows down first before the other parts of the wave
what is diffraction
when a wave spread out as it passes through a gap or round an obstacle
what is displacement and what is it measured in
how far along a wave has moved from an undisturbed position. measured in metres,m. Displacement is usually the y - axis on a graph
What is amplitude
the maximum possible displacement of a wave. measured in metres
what is the crest
amplitude name for positive displacement
what is the trough
amplitude name for negative displacement
What is wavelength and what is it measured in
The distance of one whole wave cycle/oscillation. Measured in metres
what is a period of a wave and what is it measured in
The time taken for one whole wave cycle. measured in seconds
What is frequency and what is it measured in
The number of one whole wave cycle in 1 seconds. measured in hertz
what is phase
A measurement of a wave at one particular point
what is the phase difference
The amount by which one wave lags behind the other
Have to be on the same graph
At the same point of the waves e.g 2 crests
How do you calculate frequency? (period)
f = 1/period
what is the symbol for wavelength
lambda
What are the 2 ways to measure the parts of a wave cycle (not in metres)
degrees and radians (as in pi = 3.1415926535)
Give me 1/4 , 1/2, 3/4 and 1 wave cycle in degrees
1/4 = 90 degrees
1/2 = 180 degrees
3/4 = 270 degrees
1 = 360 degrees
give me 1/4, 1/2, 3/4 and 1 wave cycle in radians
1/4 = pi/2
1/2 = pi
3/4 = 1.5 pi or 3 pi/2
1 = 2 pi
What is phase difference measured in
degrees
Whta happens if you have 2 waves with different amplitudes but the same frequencyin terms of phase difference
You get a phase difference of 0 degrees as amplitude doesnt matter when calculating phase difference
What is a transverse wave
A wave which has oscillations perpendicular to the energy propagation (transfer) of the wave
Are em waves transverse waves
yes all of them are
What are em waves
they are vibrating electric and magnetic fields
What are some examples of transverse waves
- em waves
- ripples in water
- earthquake shock waves (S-waves)
What is a longitudinal wave
A wave where the oscillation is parallel or along the energy propagation
What are examples of a longitudinal wave
sound and earthquake shock waves (P-waves)
What are the 2 main parts of a sound wave
rarefactions and compressions of the medium
what is a rarefaction
when the matter along a sound wave is spaced out
what is a compression in a sound wave
the bit of the wave when the matter is compressed
What is a polarised wave
a wave that only oscillates in one direction
what does a polarising filter do
it only transmits vibrations in one direction
What is light (in terms of wave vibrations)
a mixture of waves that have different directions of vibrations
what happens if you have two polarising filters at right angles
then no light will get through
Why does 2 polarising filters at right angles not let light through
theres a lot to explain which wont fit in the card so heres a video that explains it: https://www.youtube.com/watch?v=JWy0QsBZgbk&list=PLlDtVvefFYT9NxoJ70Ns7Htg9Um2gUPRP&index=9
What happens if 2 polarsing waves arent at right angles
The intensity of the wave will just be reduced
Can polarisation happen for all waves
no, only for transverse waves
What are some applications of polarised light
glare reduction, TV and radio signals
What evidence proves the nature of transverse waves
light was discovered to be slightly polarised by reflection in 1808. Light was thought of as a longitudinal wave back then so it confused the scientists but in 1817 a scientist suggested light was a transverse wave made up of magnetic and electrical field which oscillate perpendicular to the direction of energy propagation which explains why light can be polarised
How does glare reduction work
Light reflected of objects light water or tarmac or glass is partially polarised which can enter your eyes to cause glare. With a polarising filter at the right angle you can block out some of the light reducing the light intensity while still allowing some light through.
How does TV and radio signals work with polarised waves
TV and other aerial signals are partially polarised cause of the orientation of the transmitting rod. This means to get a strong signal you have to align the receiving and transmitting rods together to get the strongest signal.
What is antiphase
When the phase differences is exactly 180 degrees
What is a stationary wave
A wave caused by 2 progressive waves with the same frequency and amplitude moving in opposing directions superposing; causing no energy to be transferred
What is destructive superposition
When there is a phase difference of 180 degrees causing a wave to be formed which has the amplitudes subtracted
what is constructive superposition
when there’s a phase difference of 0 degrees causing a wave to be formed where the amplitudes are added
How can you demonstrate a stationary wave
a piece of string with an oscillator on one end and an object which can reflect the wave on the other end.
What is resonant frequency
The amount of waves it takes for the wave produced by an oscillator to be reflected in time for another wave to be produced. Then the original and reflected wave will interfere constructively at antinodes and destructively at nodes. link: https://www.youtube.com/watch?v=pBHxnf7k7PU
what is a node
point on a wave where the amplitude is 0m
what is an antinode
The crest on a wave (the points of maximum amplitude
what interference happens at nodes
destructive interference
what interference happens at antinodes
constructive interference
When is a stationary wave formed at resonant frequency
hint: wavelengths
When an exact number of half wavelengths fit on a string
what are the harmonic and how many nodes and antinodes do they each have
harmonics are how many half wavelengths there are. e.g 3rd harmonic= 3 half wavelengths
nodes per harmonic = harmonic +number 1 e.g 3rd harmonic = 3 + 1 = 4 nodes
antinodes = harmonic number e.g 3rd harmonic = 3 anitnodes 1st harmonic = 1 antinode
How do you setup for a stationary microwave
by having a microwave transmitter emit microwaves at a metal plate which reflect the plate. The nodes and antinodes can be detected by having a probe connected to a loudspeaker
how do you setup for a stationary soundwave
loudspeaker connected to a tube of glass with air and powder.
How can u calculate the speed of sound in a stationary soundwave
the powder in the glass are the nodes which are half of the wavelength so you can measure that distance and double it to get the distance of 1 full wave cycle
What is the equation for the frequency of any harmonic
f = (1/2L)(square root of (T/mu))
L = length of string
T = tension of the string
mu = mass per unit length
