Two monochromatic (wavelength `=a//5`) and coherent sources of electromagnetic waves are placed on the x-axis at the point (2a,0) and `(-a,0)`. A detector moves in a circle of radius `R(gt gt 2a)` whose centre is at te origin. The number of maximas detected during one circular revolution by the deterctor are -

Options

A. 60
B. 15
C. 64
D. none

Answer

A

Explanation

For point `P,Deltax=3a=15lamda` and at point Q it is also `15 lamda` somewhere at point B, it it zero thus in half part of the circle available maxima
`15xx2=30`
Thus total maxima `=2xx30=60`