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MCQEasyJEE 2023Characteristics of EM Waves

JEE Physics 2023 Question with Solution

Given below are two statements:

Statement I: Electromagnetic waves are not deflected by electric and magnetic fields.

Statement II: The amplitude of the electric field and the magnetic field in electromagnetic waves are related as E0=μ0/ϵ0 B0E_0 = \sqrt{\mu_0 / \epsilon_0} \, B_0.

Choose the correct answer:

  • A

    Statement I is true but Statement II is false

  • B

    Both Statement I and Statement II are true

  • C

    Statement I is false but Statement II is true

  • D

    Both Statement I and Statement II are false

Answer

Correct answer:A

Step-by-step solution

Standard Method

Given: Two statements about electromagnetic waves are to be checked.

Find: Which option correctly identifies the truth values of Statement I and Statement II.

For electromagnetic waves, the electric and magnetic field amplitudes satisfy

E0=cB0E_0 = c B_0

Also,

c=1μ0ϵ0c = \frac{1}{\sqrt{\mu_0 \epsilon_0}}

Therefore,

E0=1μ0ϵ0B0E_0 = \frac{1}{\sqrt{\mu_0 \epsilon_0}} B_0

So the relation E0=μ0/ϵ0 B0E_0 = \sqrt{\mu_0 / \epsilon_0} \, B_0 is incorrect.

Statement I is true, because electromagnetic waves do not get deflected by external electric or magnetic fields.

Statement II is false, because the correct relation is E0=cB0E_0 = c B_0.

Therefore, the correct option is A.

Common mistakes

  • Using E0=μ0/ϵ0 B0E_0 = \sqrt{\mu_0 / \epsilon_0} \, B_0 instead of the standard relation. This is wrong because the correct amplitude relation is E0=cB0E_0 = cB_0 with c=1/μ0ϵ0c = 1/\sqrt{\mu_0 \epsilon_0}. Always substitute the expression for the speed of light carefully.

  • Assuming electromagnetic waves are deflected like charged particles. This is wrong because electromagnetic waves are not charged objects moving through fields in that sense. Treat them as self-propagating oscillating fields, not as particles with electric charge.

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