Which of the following statements is correct in relation to electromagnetic waves in an isotropic medium? <br> <br> (a) Energy due to electric field is equal to that due to magnetic field. <br> (b) Electric vector E and, magnetic vector B are in phase. <br> (c) For a given amplitude of E vector, the intensity increases as the first power of frequency f <br> (d) For cylindrical wave fronts, the amplitude of the wave varies in proportion to $ \large\frac{1}{r^2}$ , where $r$ is the radius of the wave front.

Question

$\begin {array} {1 1} (a)\;1,3 & \quad (b)\;2,4 \\ (c)\;1,2 & \quad (d)\;2,3 \end {array}$