If 30 beats are produced in 1 second, the difference in frequencies between two sounds waves traveling through a medium along a common path at the same time must be

Beat are produced when two sounds of different frequency superimposed in the medium

Here beats are defined as number of maximum intensity that we heard during the superposition

So here we have

so difference of two frequency must be same as number of beats heard in 1 second

so here

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.