A dipole of moment \vec{p}, oscillating at frequency \omega, radiates spherical waves. The vector potential at large distance is \vec{A}(\vec{r})=\frac{{\mu }_{0}}{4\pi }i\omega \frac{{e}^{ikr}}{r}\vec{p} To order \left( \frac{1}{r} \right) the magnetic field \vec{B} at a point \vec{r}=r\hat{n} is

Radiations — CSIR Net PYQ (Question 1)

A Radiations previous-year question (PYQ) from Electromagnetism (CSIR Net). Read the question, check the correct answer, then practise the full topic.

Question 1 of 6 · 5.0 marks

A dipole of moment

p

, oscillating at frequency

ω

, radiates spherical waves. The vector potential at large distance is

A (r) = \frac{μ _{0}}{4 π} iω \frac{e ^{ik r}}{r} p

To order

(\frac{1}{r})

the magnetic field

B

at a point

r = r \overset{n}{^}

1 $- \frac{μ _{0}}{4 π} \frac{ω ^{2}}{C} (\overset{n}{^} \cdot p) \overset{n}{^} \frac{e ^{ik r}}{r}$
2 $- \frac{μ _{0}}{4 π} \frac{ω ^{2}}{C} (\overset{n}{^} \times p) \frac{e ^{ik r}}{r}$
3 $- \frac{μ _{0}}{4 π} ω^{2} k (\overset{n}{^} \cdot p) p \frac{e ^{ik r}}{r}$
4 $- \frac{π _{0}}{4 π} \frac{ω ^{2}}{C} p \frac{e ^{ik r}}{r}$

Correct answer: Option 2

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