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# A radio wave of intensity $I$ is reflected by a surface. The intensity $(I)$, if pressure exerted on the surface is $2 \times 10^{-8} N/m^2$ , will be:

$\begin {array} {1 1} (a)\; 3 N/m^2 & \quad (b)\;4 N/m^2 \\ (c)\;6 N/m^2 & \quad (d)\;7 N/m^2 \end {array}$

$I= \large\frac{pressure(p)}{c}$
$=\large\frac{ 2 \times 10^{-8} \times3 \times 10^8}{2}$
(dividing by 2, since on reflecting $I$ doubles)
$= 3 N/m^2$
Ans : (a)