progressive waves, transverse and longitudinal Flashcards
What is a progressive wave?
a progressive wave (moving wave) carries energy from one point to another without transferring the medium/material itself.
Buoy analogy
imagine a buoy bobbing up and down on a water wave - the buoy doesn’t move from its location except to move up and down as the wave passes
What are waves caused by?
a wave is caused by something making particles or fields (e.g. electric/magnetic) oscillate (or vibrate) at a source (therefore).
e.g. water waves are made of water particles moving up and down therefore.
What do these oscillations do as a result?
these oscillations pass through the medium (or field) as the wave travels, carrying energy with it so.
What happens to the energy following this?
a wave transfers this energy away from its source - so the source of the wave loses energy therefore.
List some ways you can tell waves carry energy
Electromagnetic waves causes things to heating.
• X-rays and gamma rays knock electrons out of their orbits, causing ionisation.
• Loud sounds causing large oscillations of air particles which can make things vibrate therefore.
List the three things waves can do
waves can be reflected, refracted and diffracted.
what is the reflection of a wave?
When a wave hits a reflecting surface, it bounces outwards at the same angle as it came in.
the wave is bounced back when it hits a boundary (see Figure 2). E.g. you can see the reflection of light in mirrors.
what is refraction?
the wave changes direction as it enters a different medium (see Figure 3). The change in direction is a result of the wave slowing down or speeding up therefore.
what is diffraction?
the wave spreads out as it passes through a gap or round an obstacle (see Figure). E.g. you can hear sound from round a corner.
list the properties of a progressive wave.
- displacement
- amplitude
- wavelength
- period
- frequency
- phase
- phase difference
what is the displacement of a wave?
displacement (x) of a wave is the distance of a point on a wave from its equilibrium position
measured in metres.
buoy analogy - the displacement would be how high the buoy is above sea level, or how low it is below sea level.
what is the amplitude of a wave?
amplitude (A) is the maximum displacement of a wave from its equilibrium/undisturbed position.
measured in metres, the distance between successive peaks/ troughs therefore
buoy analogy - the amplitude of a bubbling buoy would be the distance from the undisturbed position (sea level) to the highest point it reaches above sea level, or the lowest point it reaches below sea level
what is the wavelength of a wave?
wavelength (lambda) is the length of one whole wave oscillation or wave cycle, e.g. the distance between two successive crests (or troughs)
measured in metres. waves with different frequencies and wavelengths can have very different properties overall.
what is the period of a wave?
- the time taken for one whole wave cycle/the time taken for one complete oscillation.
measured in seconds (s)
e.g. the time it takes a buoy to go from its highest point, back to its highest point again
what is the frequency of a waves?
- the number of complete/whole wave cycles (oscillations) per second passing a given point.
what is the phase of a waves?
a measurement of the position of a certain point along the wave cycles.
what is the phase difference of a wave?
the amount by which one wave lags behind another waves so.
what can phase and phase difference be measured in?
Angles (degrees or radians) or in fractions of a cycle therefore
what is the equation for calculating the frequency?
frequency = 1/time period
Frequency (Hz)/s^-1, Time period (s)
state the wave equation for waves.
c = fλ
wave speed = frequency x wavelength
c = wave speed in ms^-1
f = frequency in Hz (=s^-1)
λ = wavelength in m
- the wave equation links the speed, frequency and the other wavelength of a wave.
- this is relevant for both transverse and longitudinal waves therefore.
how can you calculate the wave speed?
c = d/t
wave speed = distance/time
c = wave speed in ms^-1
d = distance in m
t = time in s
what does the wave equation state for a constant speed?
the wave equation shows it for a wave of a constant speedo therefore:
- as the wavelength increases, the frequency decreases
- as the wavelength decreases, the frequency increases.
how can you derive the wave speed equation?
You can derive the wave speed equation by imagining how long it takes for the crest of a wave to move across at a distance of one wavelength therefore
- the distance travelled is the wavelength, λ
- the time taken to travel one wavelength is the period of the waves, which is equal to the equation 1/f.
now substitute these values into the normal wave speed question above to get the speed of a wave in terms of the certain wavelength and frequency therefore:
speed (c) = distance moved (lambda)/time taken (1/f)
dividing something by 1/f is the same as multiplying it by f.
so from this you get the wave speed equation shown above so:
c=lambda/(1/f) = fxlambda