AIIMS 2007 Physics Production of Electromagnetic Waves Assertion Reason Question

To analyze the question effectively, let's break down the assertion and the reason, and determine their validity and relationship.

Assertion: Dipole oscillations produce electromagnetic waves.

This statement is indeed true. An oscillating electric dipole, which consists of two equal and opposite charges separated by a small distance, generates a time-varying electric field. According to Maxwell's equations, specifically Faraday's law of induction and the Ampère-Maxwell law, a time-varying electric field produces a magnetic field, and a time-varying magnetic field produces an electric field. This interplay leads to the propagation of electromagnetic waves. The frequency of the emitted waves corresponds to the oscillation frequency of the dipole.

Reason: Accelerated charge produces electromagnetic waves.

This statement is also true. According to classical electrodynamics, an accelerating charge emits electromagnetic radiation. The physical intuition behind this is that as the charge accelerates, it disturbs the surrounding electric field, creating a changing configuration of the electric and magnetic fields that propagates outward as electromagnetic waves. This principle is described by the Larmor formula, which gives the power radiated by a non-relativistic accelerating charge, expressed as:

$P = \frac{2}{3} \frac{q^2 a^2}{c^3}$

where $P$ is the power radiated, $q$ is the charge, $a$ is the acceleration, and $c$ is the speed of light in a vacuum.

Relationship between Assertion and Reason

The reason correctly explains the assertion because dipole oscillations involve charges that are accelerating (as they move back and forth), which leads to the production of electromagnetic waves. Thus, the reason is a valid explanation for why dipole oscillations produce these waves.

Conclusion

Since both the assertion and reason are true, and the reason accurately explains the assertion, the correct answer is:

A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Clarification on Other Options

• B) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

  • This option is incorrect because the reason does indeed explain why dipole oscillations produce electromagnetic waves.

• C) Assertion is true but Reason is false.

  • This is incorrect since both the assertion and reason are true.

• D) Both Assertion and Reason are false.

  • Clearly incorrect, as both statements are true.

Summary

In summary, electromagnetic waves are produced by oscillating dipoles due to the fact that the oscillation involves acceleration of charges, which are known to radiate energy in the form of electromagnetic waves. Both the assertion and reason are true, and the reason supports the assertion directly, making option A the correct choice.