Sunday, April 26, 2009
Wave InterferenceDefinition: phenomenon which occurs when two waves meet while travelling along the same medium
There are mainly two types of wave interference: constructive and destructive
Constructive
When two waves which both have the same displacement direction, they will create a stronger wave with a higher intensity. So in layman’s term: When two waves that are travelling along a line and both are curved in a “u” or “n” shape meets each other, they will form a bigger wave. The most important requirement is that both waves have the same displacement direction. o.O
Here’s a couple illustrations taken from the website: http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/waves/u10l3c.html to depict what have been explained earlier.
As seen down here, two waves (represented by red and blue) of the same displacement direction (i.e. both are curved in an ‘n’ shape) meet each other to form a stronger wave (represented by green wave)
Destructive
So the opposite of constructive interference is destructive interference. As the name suggest, the waves destroy each other when they meet, hence cancelling each other out and no sound is heard.
This is also known as the creation of dead spots, which are basically places where no sound can be heard.
Destructive interference occurs when two interfering waves of different displacement direction meet each other, which will result in cancellation.
Ok, sounds cheem, but here’s another picture to help! ^^
So as seen in the two illustrations, two waves of opposite displacement direction (represented by red and blue again) meet each other and result in the cancellation, as seen by the green line.
However, destructive interference does not mean total destruction of the sound waves. As mentioned earlier, the result of destructive interference is cancellation. To be more precise it means that the affect of one of the pulses on the displacement of a given particle of the medium is destroyed or canceled by the affect of the other pulse when the two pulses overlapped each other, as quoted from the same website http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/waves/u10l3c.html
Superposition
We are currently still struggling to understand the concept of superposition. All that our group can understand now is that superposition is somehow applied to find the shape of the resultant wave during interference.
Anyway in our case, it would be more logical to place the sofa where the audience will be sitting at the point where there is constructive interference. However the problem is how do we determine the point where there is constructive interference? We may probably search more on the website or ask the lab technician one of these days.
Here’s a picture featuring our solution on the location of the audience.
So as seen in this picture, it would be best if we can position the seat at point A or B, which is experiencing constructive interference. The other points are suffering from destructive interference. In the picture, intersecting points between waves of different thickness means destructive interference while intersecting points between waves of equal thickness means constructive interference.
Ok, so now let’s move on to diffraction.
Diffraction
Definition: Diffraction basically refers to the phenomena experienced when a wave encounters an obstacle
Factors affecting diffraction
Wavelength – we will not be able to change the wavelength in this case, even though it may affect diffraction
Size of the Slit – Since we are trying to put as little obstacles between the speaker and the audience, diffraction doesn’t come in handy. However, it is essential when it comes to the sealing of the studio. Sound may come in from the outside of the room and diffracts when passing through any hole in the wall which may cause dramatic effects.
So, another point of our solution is that we have to seal off whatever possible slits that may be present in the wall.
here is the updated mindmap:
