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    Since E represents Energy/unit time;

    E = Watts = Power

    Intensity of wave = E/m2

    Since the Amplitude is doubled the Intensity increases by a factor of four.

    Hence, intensity is 4E/m2

    Thus, the energy reaching the area per unit time is 4E

    However, the answer is 2E.

    Why ?
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    You have forgotten to take account of the fact that the question states that the surface area is smaller by a half. Half the area and you half the amount of energy received.
 
 
 
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