Triple Waves Flashcards
What happens during diffraction in water waves?
When straight water waves are directed towards a narrow gap between two barriers, they curve and spread out after passing through. This is diffraction.
* There is no change in wavelength
What does the amount of spreading of waves during diffraction depend on?
The amount of spreading depends on how the size of the gap compares to the wavelength of the waves:
if the gap side is comparable to the wavelength, then the spreading is substantial
if the gap size is much larger than the wavelength, the spreading is much less noticeable
What else should you remember about diffraction?
A gap is just two edges, and that in fact waves will ‘band round’ past a single edge e.g. radio waves that are diffracted as they pass over hills
What other types of waves can be diffracted?
All waves - transverse and electromagnetic
What does the gap have to be like for the diffraction of light waves?
Because the wavelength of light is so small, a very small gap has to be used to demonstrate the effect.
In practice a slit about 0.1mm wide is used: while this is clearly much larger than the wavelength, enough spreading is produced to be observable
What is an analogue signal?
One that has a wide range of continuously varying levels- like a sound recorded by a microphone and stored on a vinyl disc
Analogue signals are initially a very faithful ‘record’ of an event, but are very susceptible to interference
What would happen if a light wave was carrying an analogue signal?
It would mean that the brightness of the wave would vary with the amplitude signal
What is a digital signal?
One that has only two levels (on or off, 1 or 0). It represents a binary number.
What would happen if a light wave were carrying a digital signal?
The light would be either on or off
How can analogue signals be turned into digital signals?
By the process of sampling - this involves measuring how big the analogue signal is several times during each cycle and then turning the results into binary numbers
How can better quality digital signals be obtained from sampling?
By using a higher sampling rate - 44kHz - i.e. 44,000 samples a second has long been used for CD quality music
By using a higher sampling resolution - e.g. 24 bit (with 16,777,216 levels) rather than 16 bit (with 65,536 levels)
Why is some information lost as analogue signals are turned into digital ones during the sampling process?
Because the analogue signal may change significantly between samples
What are the advantages of using digital signals rather than analogue signals?
1) digital signals are less prone to inference - even if the pulses get degraded or deformed as the signal is transmitted, no information is lost as long as you can tell there is still a pulse there, so, for example digital radio is clearer than analogue radio, and digital TV has sharper pictures
2) compression techniques enable digital signals to be reduced in size - e.g. MP3 encoding, JPEG image compression
3) digital signals can be manipulated much more easily, as in image processing
How can digital signals be made to carry more information?
1) increased frequency
2) using an additional signal level
3) transmitting multiple signals at the same time with just one cable or EM wave
4) increase the bandwidth - bandwidth is the amount of space on the carrier wave, the range of frequencies you need to accommodate the carrier wave and the information it is carrying
5) compress a digital signal that fits into a smaller bandwidth - this is done by sending the new information e.g. things in an image that have changed, if the image remains the same, no more information is sent
What is the wavelength of sound waves?
Roughly 1m
