Question

An oscillating electric dipole of moment $\overrightarrow{d}(t) = d_0 \cos(\omega t) \hat{z}$ is placed at the origin as shown in the figure. Consider a point $P(r, \theta, \phi)$ at a very large distance from the dipole. Here, $r$, $\theta$, and $\phi$ are spherical polar coordinates. Which of the following statements is/are true for the intensity of radiation?

• A. Intensity is zero if P is on the z axis
• B. Intensity is zero if $P$ is on the $z$ axis.
• C. Intensity at $P (r = R, \theta = \pi \, / \, 2, \phi = \pi \, / \, 4)$ is greater than that at $P (r = R, \theta = \pi \, / \, 4, \phi = \pi \, / \, 4)$.
• D. Intensity at $P (r = R, \theta = \pi \, / \, 2, \phi = \pi \, / \, 4)$ is equal to that at $P (r = R, \theta = \pi \, / \, 4, \phi = \pi \, / \, 4)$.

Answer 1

Answer: (A), (C)

Intensity is zero if P is on the z axis

Answer 2

The correct Answers are (A):Intensity is zero if P is on the z axis ,(C):Intensity at $P (r = R, \theta = \pi \, / \, 2, \phi = \pi \, / \, 4)$ is greater than that at $P (r = R, \theta = \pi \, / \, 4, \phi = \pi \, / \, 4)$.