A source emits electromagnetic waves of wavelength $$3$$ m. One beam reaches the observer directly and other after reflection from a water surface, 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

Question

Infinity Learn · Accepted Answer

We know that a phase change of π  occurs when the reflection take place  at the boundary of denser medium.   Due to geometry,  ∆ϕ$$1$$ $$=$$ $$2$$πλ∆x        $$=2$$$$π$$$$31.5=$$π   radian. Due to phase change,   ∆ϕ$$2$$ $$=$$ π   radian  ∴Total phase difference of second wave  when it reached the observer   ∆ϕ$$=$$∆ϕ$$1+$$∆ϕ$$2=2$$π   radian  Resultant intensity $$=$$  $$I1+I2+2I1I2cos$$ϕ                                     $$=I+I4+2$$.$$I2cos2$$π$$=5I4+I=9I4$$

A source emits electromagnetic waves of wavelength 3 m. One beam reaches the observer directly and other after reflection from a water surface, 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

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