Waves And Particle Nature Of Light Spec Points Flashcards
Amplitude
A wave’s maximum displacement from the equilibrium position
Frequency
The number of complete oscillations passing through a point per second
Period
Time taken for one full oscillation
Speed
Distance travelled by the wave per unit time
Wavelength
The length of one whole oscillation (e.g. the distance between successive peaks/troughs)
Longitudinal waves in terms of pressure variation
Pressure is decreased in the rarefactions and increased in the compressions
Longitudinal waves in terms of the displacement of particles
Rarefaction - neighbouring particles move away from each other
Compression - neighbouring particles move towards a point
What is the speed of all EM waves in a vacuum
3e8 ms-1
CP06: speed of sound using 2-beam oscilloscope, signal generator, speaker and microphone
Variables and equipment
IV - distance
DV - phase of received signals
CV - same location to carry out the experiment
- for each set of readings, the same frequency of sound
- signal generator with loudspeaker
- oscilloscope with 2-beam facility
- microphone
- 2 metre rulers
- connecting leads
CP06: speed of sound using 2-beam oscilloscope, signal generator, speaker and microphone
Method
- connect microphone and signal generator to an oscilloscope and set up the signal generator about 50cm from microphone
- set the signal to abt 4kHz
- the oscilloscope should trigger when the microphone detects a sound, adjust the time base so that the signal from the generator and the microphone can be on the screen with about three cycles visible
- adjust the separation so a trough on the upper trace coincides with a peak on the lower trace (this makes judging the point where the waves coincide easier)
- record the distance between the microphone and the signal generator (distance one, d1)
- move the microphone further away, watch the traces on the screen
- when the next trough and peak coincide, record the new distance (d2)
- repeat as many times as possible in the available space
- calculate the mean wavelength of the sound
- using the oscilloscope trace find the frequency of the sound
- reduce the frequency to around 2kHz and repeat
CP06: speed of sound using 2-beam oscilloscope, signal generator, speaker and microphone
Analysis of results
Speed of sound - v = f(lambda)
Frequency found from time base of oscilloscope by using f = 1/T
CP06: speed of sound using 2-beam oscilloscope, signal generator, speaker and microphone
Systematic and random errors
Systematic
- ensure the scale of the time base is accounted for correctly
The scale is likely to be small (e.g. milliseconds) so ensure this is taken into account when calculating frequency
- use the oscilloscope signal trace to find frequency to avoid relying on the dial of the signal generator
Random
- reduce by doing repeat readings and taking an average in measurements
- the time interval is small so make the distance between the microphone and signal generator as large as is practical
CP06: speed of sound using 2-beam oscilloscope, signal generator, speaker and microphone
Safety considerations
- the voltage and current are low, so normal care with electrical equipment is sufficient
- keep sound at a normal listening volume to avoid damage to hearing
Phase
The position of a certain point on a wave cycle. This can be measured in radians, degrees or fractions of a cycle
Phase difference
How much a particle/wave lags behind another particle/wave. This can be measured in radians, degrees or fractions of a cycle
Path difference
The difference in the distance travelled by two waves
Superposition
Where the displacements of two waves are combined as they pass each other, the resultant displacement is the vector sum of each wave’s displacement.
Coherence
A coherent light source has the same frequency and wavelength and a fixed phase difference
Wavefront
A wavefront is a surface which is used to represent the points of a wave which have the same phase
Two types of interference are -
And they occur during -
Constructive, destructive, superposition
Constructive interference
Occurs when two waves are in phase and so their displacement is added
Destructive interferecne
Occurs when the waves are completely out of phases and so their displacements are subtracted
If two waves are in phase …
They are both at the same point of the wave cycle, meaning they have the same frequency and wavelength (are coherent) and their phase difference is an integer multiple of 360degrees
Two waves will be completely out of phase when …
They are coherent and the phase difference is an odd integer multiple of 180 degrees