In: Physics
The beat wavelength lbeat is much longer than that of either superposed wave , l1 and l2. Demonstrate this. They relate as lbeat-1 = (1/2)( l1-1 - l2-1) (hint: remember the condition for the formation of beats, and state it mathematically. If it takes more than a couple of lines, you are on the wrong track)
Now one of the fundamental requirement for the formation of
beats is that the 2 waves must have nearly equal frequencies, this
means that their wavelengths must also be nearly equal, since
where
is the frequency and
is the wavelength and
is the speed of propogation of the wave in that medium. Since both
the waves are assumed to be travelling in the same medium, their
are same. Hence, if their
are nearly equal, their
would also be nearly equal. Coming back to the relation, this
would mean that the denominator
Becomes very large. Hence,
becomes very large compared to either superposed wave.