A source emits electromagnetic waves of wavelength `3 m`. One beam reaches the observer directly and other after reflection from a watersurface, travelling `1.5 m` extra distance and with intensity reduced to `1//4` as compared to intensity due to the direct beam alone. The resultant intensity will be :

Options

A. `(1//4) fold 3`
B. `(3//4)fold`
C. `(5//54)fold`
D. `(9//4)fold`

Answer

d

Explanation

We know that a phase change of `pi` oocures when the reflection takes place at the boundaruyb of denser medium ,.This is equivalent to a path difference of `lamda//2`
`therefore Total phase dffeece =pi-pi=0`
Thus,the two waves superimpose in phase
Resultant amplitude =`sqrt(I)+sqrt(I/4)=3/2sqrt(I)`
Resultant amplitude =`(3)/(2)sqrt(I))^(2)=(9)/(4)I=(9)/(4)fold`