Consider a source of sound `S` and an observer `P`. The sound source is of frequency `n_0`. The frequency observed be `P` is found to be `n_1` if `P` approaches `S` at speed `v` and `S` is stationary, `n_2` If `S` approaches `P` at a speed `v` and `P` is stationary and `n_3` if each of `P` and `S` has speed `(v)/(2)` towards one another Now.

Options

A. `n_1=n_2=n_3`
B. `n_1ltn_2`
C. `n_3gtn_0`
D. `n_3` lies between `n_1` and `n_2`

Answer

B, C, D

Explanation

When observer `P` approaches the statinary source at speed `v`.
`n_1=(V+n)/(V)xxn_0` .(i)
(V is speed of sound)
When source `S` approaches the stationary observer `P` at speed `v`
`n_2=(V)/(V-v)xxn_0` ..(ii)
Thus, `n_2gtn_1`, i.e., choice (b) is correct when both `S` and `P` approach each other with speed `(v)/(2)`
`n_3=(V+((v)/(2)))/(V-((v)/(2)))n_0` .(iii)
Hence `n_3gtn_0` and `n_3` lies between `n_1` and `n_2`.