Topic 6: Waves
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Describe the method of the ripple tank practical
Frequency: - put a stop clock on the screen - use a digital camera to record the waves passing a point - replay in slow motion and count the number of waves passing a point per second (Or read frequency off the oscillator) Wavelength: - place a metre rule at the side of the screen perpendicular to the wave fronts - take a photograph of the shadow on the screen - use the metre rule to measure the distance between two wave fronts - measure 10 waves then divide by 10 to find one wave Wave speed = frequency x wavelength
What is the equation find the period of a wave?
Period = 1/frequency
What is period and frequency measured in?
• period (T) is measured in seconds (s) • frequency (F) is measured in hertz (Hz)
Define wave speed
The speed at which the energy is transferred (or the wave moves) through the medium
What is the equation that links wave speed, frequency and wavelength? (Give units)
Wave speed (m/s) = frequency (Hz) x wavelength (m)
What is the amplitude of a wave?
The maximum displacement of a point on a wave away from its undisturbed position
What is the wavelength of a wave?
The distance from a point on one wave to the equivalent point on the adjacent wave
What is the frequency of a wave?
The number of waves passing a point each second
Explain why for both ripples on a water surface and sound waves in air, it is the wave and not the water or air itself that travels
The wave is moving not the median (like a Mexican wave - the people don’t move but the wave does)
Describe the differences between transverse and longitudinal waves in terms of the structure
Transverse waves - peaks and troughs Longitudinal waves - compressions and rarefactions
Describe the differences between transverse and longitudinal waves in terms of the vibration
Transverse waves - 90 degrees to direction of energy transfer Longitudinal waves - parallel to direction of energy transfer
Describe the differences between transverse and longitudinal waves in terms of vacuum
Transverse waves - only electromagnetic waves can travel in vacuum Longitudinal waves - cannot travel in a vacuum
Describe the differences between transverse and longitudinal waves in terms of the material
Transverse waves - can move in liquids and solids, but not in gases Longitudinal waves - can move in gas, liquids and solids
Describe the differences between transverse and longitudinal waves in terms of density
Transverse waves - constant density Longitudinal waves - changes density
Describe the differences between transverse and longitudinal waves in terms of pressure
Transverse waves - pressure is constant Longitudinal waves - changes in pressure
Describe the differences between transverse and longitudinal waves in terms of the speed of wave
Transverse waves - dependant on material it is travelling in Longitudinal waves - dependant on material it is travelling in
What are the two types of waves?
Transverse and longitudinal
Give an example of transverse waves
The ripples on a water surface, EM waves, vibration on a guitar string
Give an example of longitudinal waves
Sound waves travelling through the air, ultra-sound
What are the control variables for the waves on a string practical?
• number of masses as it controls tension of string • length of string - affects how many waves produced • type of string - affects how many waves produced
Describe the method for the waves on a string practical
1) switch the signal generator and vibration generator on so the string vibrates up and down 2) move the wooden bridge until a clear wave pattern is formed between the wooden bridge and the vibration generator 3) use a metre rule to measure the length of the string between the wooden bridge and the vibration generator 4) record the frequency of the wave from the signal generator 5) record the number of loops in the wave pattern 6) change the frequency on the signal generator until a new wave pattern is formed 7) repeat steps 4-6