Waves
There are two types of waves: longitudinal and transverse
Longitudinal waves: the oscillations are parallel to the direction of energy transferred
Transverse waves: the oscillations are perpendicular to the direction of energy transfer
Waves transfer energy from one place to another
In longitudinal waves, compressions are the parts where the particles are close together and the refraction are the parts where the particles are spread out
Longitudinal waves only travel through a medium (air, liquid or solid)
Not all transverse waves require a medium to travel
Properties of waves: amplitude, frequency, period and wavelength
Amplitude (M) = maximum displacement of a point on a wave away from its undisturbed position
Wavelength (M)= distance from a point on a wave to the equivalent point on the adjacent wave
Frequency (Hz) = number of waves passing a point each second
Period (s) = time in seconds for one wave to pass a point
Wave speed = the speed at which a wave moves to travel a medium
Wave speed = frequency x wavelength (v = f x λ)
Practical for wave speed:
Two people are apart by 500 metres
Person A has two cymbals and person B has a timer
Person B starts the timer once they see Person A clash the cymbals together
Person B then stops the times when they hear the cymbals clash
The speed is then calculated using the equation speed = distance/time
Limiting factors:
Every person has a different reaction time
There will a be a fraction of second between seeing the cymbals clash and starting the timer
There will be a fraction of second between hearing the cymbals clash and starting the timer
This can be solved by having many observers and calculating a mean after (excluding any anomalous results)
The time between seeing and hearing the cymbals is very short.
This can be solved by increasing the distance between the two people
Required practical 8:
Equipments:
Ripple tank
Vibration bar
Power pack
Lamp
White sheet of paper
Ruler
Timer
Purpose of the method: observe the features of water waves
Turn of the vibration bar using the power pack
When the vibration bar vibrates, it creates waves across the surface of the wave
Turn on the lamp on top of the ripple tank
The lamp shines the water waves on the paper below the ripple tank
You can record the paper and the timer beside it with a mobile phone in order to investigate the frequency, wavelength and speed as you can freeze or slow down the image.
Use the recording to find the wavelength: place a ruler on the paper, measure the distance between one wave and ten waves further. Then, divide the distance by 10 to find the wavelength of one wave.
Frequency: Place a timer next to the paper and count how many waves pass across a certain point every 10 seconds and divide the number of waves by 10
Speed: use the formula wave equation to measure or measure the time taken to move the length of the tank and use the formula s=distance/time
Required Practical 8: waves in a solid
A string is attached to a vibration generation and a hanging mass which makes the string taut; the vibration generator is attached to a single generator which allows us to change the frequency of the waves. You won’t be able to see the waves but at some frequency a standing wave will form due to resonance. This is what happens in a guitar.
To measure the wave length: Measure the distance from the wooden bridge to the vibration generator. Then divide the total length by the number of half wavelengths and times by 2
Reflection of waves:
You can use the wavelength to find speed by using the wave equation.
Passing through another material cannot change a wave. However, in some cases waves can change direction when they pass from one material to another. This is called refraction.
The energy of a wave could be absorbed by a material. If this happens the wave might have not passed through the material at all.
The wave may be reflected from the off the surface of the object
The angle of incidence = the angle of reflection
The light in between the angle of incidence and the angle of reflection is the normal..