12: Interference Lab - 1
12. PRELAB FOR INTERFERENCE
As you have seen in your studies of standing waves, a wave and its reflection can
add together “
” (peak meets peak, giving large amplitude) or
” (peak meets valley, canceling each other).
This type of
, and it depends on the relative
of the interfering waves.
the direct and reflected waves are coming from the same source, they clearly start out
Whether or not they come back together in phase depends on path length.
difference in the two path lengths is 1,2,3,etc.
, then the waves will be back
If there is an extra ½ wavelength, however, they will be out of phase.
AN EXAMPLE OF MICROPHONE PLACEMENT
The next page contains an excerpt from an article on the importance of a
Read the excerpt and answer the following questions:
When the pressure wave is reflected from the table, is there a 180
(Think back to the standing waves in the open and closed tubes).
Look at Fig. 4.10 from the excerpt.
Suppose that the direct sound travels 2
meters, and the reflected sound covers a greater distance of 2 ½ meters.
difference in the two path lengths is
Constructive interference will occur when
, … , where
is the wavelength.
Use the relation v =
, (v – speed of
– frequency) to calculate the first four frequencies at which constructive
interference will occur.
= 344 m/s.
Then, calculate the first four frequencies at
which destructive interference (