Waves Flashcards
Transverse waves
🔹A transverse wave is one where the particles vibrate or oscillate perpendicular to the direction of travel (and energy transfer)
🔹These waves can be polarized.
🔹Examples include: electromagnetic waves like radio waves and visible light.
Longitudinal waves
🔹A longitudinal wave is one where the particles vibrate or oscillate parallel to the direction of travel (and energy transfer)
🔹They cannot be polarized
🔹Examples include sound and ultrasound waves.
Displacement (x)
Displacement of a wave is the distance from its equilibrium position. It is a vector quantity. It can be positive or negative.
Amplitude (A)
Amplitude is the maximum displacement of a particle in the wave from its equilibrium position.
Equilibrium position
It is the rest position.
Wavelength (λ)
The wavelength of a wave is the distance between any two points on successive oscillations of the wave that are in phase. It is measured in metres.
What is a crest and a trough?
A crest is the highest point of a transverse wave and a trough is the lowest point.
Period ( T )
The period of a wave is the time taken to produce one complete oscillation or cycle of the wave.
Frequency ( f )
The frequency of a wave is the number of complete oscillations per second. It is measured in Hertz (Hz) or s<-1.
Phase difference
The phase difference tells us how much a point or a wave is in front or behind another wave.
(Extra bits)
• This can be found from the relative position of the crests or troughs of two different waves of the same frequency.
• Phase difference is measured in fractions of a wavelength, degrees or radians.
Waves in anti-phase
When the crest of one wave aligns with the trough of another, they are in antiphase.
(Two waves with a phase difference of 180° or π)
Waves in phase
When the crests or troughs are aligned, the waves are in phase.
(Phase difference of 360° or 2π)
Progressive waves
Waves that transfer energy are known as progressive waves.
Stationary waves
Waves that do not transfer energy are known as stationary waves.
What is a time-base setting?
The period of the wave can be determined from the time-base This is how many seconds each division represents, measured commonly in s div-1 or s cm-1
Wave equation
🔹The wave equation links frequency, wavelength and speed of a wave.
🔹The wave equation tells us that for a constant speed, the wavelength is indirectly proportional to the frequency.
V = f × λ
What is “c” in c=fλ?
It is the wave speed. However, c is often used to represent a specific speed ー the speed of light ( 3 x 10<8 ms<-1).
What is wave intensity?
The amount of energy passing through a unit area per unit time is the intensity of the wave.
• Therefore, the intensity is defined as power per unit area.
What is intensity proportional to?
The intensity of a progressive wave is directly proportional to its amplitude squared and frequency squared.
• Extra
This means that if the frequency or the amplitude is doubled, the intensity increases by a factor of 4 or 2<2.
What is the inverse square law?
Note the intensity is proportional to 1/r<2
• This means when the source is twice as far away, the intensity is 4 times less.
• The 1/r2 relationship is known in physics as the inverse square law.
Some examples of transverse waves:
• Water waves
• Electromagnetic waves
• Vibration on a guitar string
Some examples of longitudinal waves:
• Sound Waves
• Pushing and Pulling of a slinky
• Ultrasound waves
What is the Doppler effect or Doppler shift?
The frequency change due to the relative motion between a source of sound or light and an observer is known as the Doppler effect. (Or doppler shift)
What is the wave velocity for sound waves?
340 m/s
All electromagnetic waves have the following properties in common:
• They are all transverse waves.
• They can all travel in vacuum.
• They all travel at the same speed in a vacuum - the speed of light (3 × 10<8 m/s).
What is the relationship between frequency and energy?
The higher the frequency, the higher the energy of the radiation.
Transverse waves can be polarised, this means:
• Vibrations are restricted to one direction.
• These vibrations are still perpendicular to the direction of propagation/energy transfer.
Can longitudinal waves be polarized?
They cannot be polarized since they travel parallel to the direction of vibration.
What is Wave motion?
Wave motion is when energy is transferred through moving oscillations and vibrations. For example in the vibration of ropes and springs.
What is a cathode ray oscilloscope?
It is a laboratory instrument used to display, analyze and measure waveforms of electrical circuits.
When is a wave coherent?
When there is a constant phase difference.
What is polarization?
When the vibrations are restricted to just one direction and they are still perpendicular to the direction of energy transfer.
