Waves Flashcards
Described transverse wave.
A type of wave in which the particles oscillate perpendicular to the direction the wave travels.
Examples of transverse waves.
EM waves, water and s-waves.
Describe a longitudinal wave.
A type of wave in which the particles oscillate parallel to the direction of wave travel.
Examples of longitudinal waves.
Sound waves and p-waves.
What is the wavelength of a wave?
It is the distance between two matching points on neighbouring waves, measured in metres.
What is the amplitude of a wave?
Amplitude is the maximum displacement of a point from the centre of oscillation, measured in metres.
The larger the amplitude the greater the what of the wave?
The greater the energy of the wave.
The period of a wave, T, is what?
The time taken for a point on the wave to move through one complete oscillation.
Frequency of a wave is measured in what?
Hertz, Hz.
Equation linking time period and frequency of a wave:
f=1/T
Where:
f is frequency in Hz.
T is time period in s.
Frequency is a measure of what?
Number of waves that pass a point in 1 second.
The wave equation is:
v=fλ Where: v is velocity in ms^-1. f is frequency in Hz. λ is wavelength in m.
Electromagnetic waves are transverse, true or false?
True.
True or false, electromagnetic waves travel at different speeds?
False, they all travel at the same speed (speed of light).
What speed do electromagnetic waves travel through a vacuum at?
3x10^8ms^-1
Typical wavelength for a radiowave is what?
10^3m to a few metres.
Typical wavelength for a microwave is what?
10^-2m
Typical wavelength for an infrared wave is what?
10^-5m
Typical wavelength of visible light is what?
10^-7m
Typical wavelength of ultraviolet light is what?
10^-8m
Typical wavelength of X-ray radiation is what?
10^-10m
Typical wavelength of a gamma ray is what?
10^-12m
EM radiation travels by what?
Oscillations in both the electric and magnetic fields.
Superposition of waves is what?
Where the waves are both causing the same particle to oscillate causing the amplitudes to be summed.
If two waves of the same wavelength and amplitude are perfectly in phase, what can be said about the amplitude of the resultant wave?
It is twice the amplitude of one of the initial waves.
When waves cause a resultant wave with a greater amplitude than the initial waves what kind of interference is this?
Constructive interference.
When two waves have the same amplitude and wavelength but are perfectly out of phase what can be said about the resultant wave?
There isn’t one. The oscillations of the waves cancel each other perfectly leaving no wave.
When two waves cause a resultant wave with less energy than the initial wave what kind of interference is that?
Destructive interference.
Waves that are perfectly out of phase have a phase difference of what?
π
Calculate what 1 rad is in degrees.
1 rad = 360/2π = 57.3 degrees
Calculate what 1 degree is in radians.
1 degree = 2π/360
Diffraction is what?
The spreading out of a wave as it passes an obstacle or goes through a gap.
In order for diffraction to occur what must be said to be true about the size of obstacle/gap and wavelength?
The obstacle/gap must be a similar size to the wavelength else the diffraction is negligible.
What happens to the energy per length of wavefront as a wavefront is being spread out by diffraction?
The energy per length of wavefront decreases.
What can be said about the overall energy of the wave as it is diffracted?
The overall energy of the wave remains the same (conservation of energy).
What happens to the amplitude of the wavefront during diffraction?
The amplitude decreases.
Huygen constructs work by assuming what?
A wavefront can be modelled as a row of oscillating particles that cause wavelets which can be connected to show a wavefront.
Diffraction grating equation linking d and N.
d=1/N
Where:
d is the distance between the slits, m.
N is the line density, m^-1.
What is the diffraction grating formula?
dsinθ=nλ Where: d is the distance between the slits, m. n is the order of the maxima. λis the wavelength, m.
Define refraction.
The changing of the direction of a wave as it changes medium.
What happens if a wave travels from a less dense into a more dense medium?
The wave bends towards the normal.
What happens if the wave travels from a more dense into a less dense medium?
The wave bends away from the normal.
What is a normal?
The perpendicular to the surface being studied.
Snell’s Law using angles:
sini/sinr = n
Or
n1sinθ1 = n2sinθ2
Snell’s Law using velocities:
v1/v2 = n
What is the absolute refractive index of a material?
The absolute refractive index for a material is the refractive index of light travelling from a vacuum into a particular substance.
Equation for finding the critical angle:
sinc = 1/n
Where:
c is critical angle.
n is the absolute refractive index of the material light is travelling out of.
What happens when i
Refraction occurs.
What happens when I=θc?
The ray is split part of it is refracted along the very edge of the prism, part is reflected back into the prism.
What happens if i>θc?
Total internal reflection occurs.
Give everyday uses of total internal reflection (excluding optical fibres).
Telescopes (lens). Medical keyhole cameras. Diamonds. Bike reflectors. Cats eyes on the road.
What are the two types of lenses?
Convex (converging) and concave (diverging).
What happens when you look at a close object (within the focal length) through a convex (converging) lens?
The image is:
Magnified
Upright
Virtual
What happens if you look at a far object (beyond focal length) through a convex (converging) lens?
The image is:
Inverted
Diminished
Real
What happens if you look at an object through a concave (diverging) lens?
The image is:
Diminished
Upright
Virtual
What is the centre of a lens known as?
The optical centre.
Where is the principle focus on a convex (converging) lens?
Where all rays converge (cross).
Where is the principle focus on a concave (diverging) lens?
When the diverging rays are traced backwards and the they all converge, this is where the principle focus is.
What is a node on a stationary wave?
A point of minimum displacement.
What is an antinode on a stationary wave?
A point of maximum displacement.
What does the first harmonic look like on a string?
The first harmonic on a string is when the wave is stationary and there is a node at each end with one antinode in the middle.
What can be said about the wavelength of the wave if the first harmonic is produced in a string?
The wavelength will be 2x the length of the string.
The fundamental frequency of a wave is the frequency when…
…the first harmonic is produced as a standing wave.
Wave speed in a string depends on what?
Length, tension and material.
Stationary waves in strings always start and end in what?
Nodes.
What can be said about the wavelength of the second harmonic in a string?
The wavelength is equal to the length of the string.
What can be said about the wavelength of the third harmonic in a string?
It is equal to 2/3 length of the string.
What can be said about the frequencies of the 2 and 3rd harmonics for a stationary wave in a string?
The frequency of the second is 2x the fundamental frequency.
The frequency of the third is 3x the fundamental frequency.
What can be said is at the start and end of a stationary wave in a closed pipe?
There is always an antinode at the open end (start) and a node at the closed end (end).
Can we get all harmonics in a closed pipe?
No we can only get odd harmonics, so 1st, 3rd, 5th etc.
Can we get all harmonics with an open pipe?
No we can only get the even harmonics.
What can be said about the start and end of a stationary wave in an open pipe?
The wave starts and ends with both antinodes.
