NEETPhysicsElectromagnetic Waves
Assertion (A): In a plane electromagnetic wave propagating in vacuum, the ratio of the instantaneous magnitudes of the electric and magnetic fields ( E/B ) is always constant and equal to c . Reason (R): In an electromagnetic wave, the electric and magnetic fields oscillate in phase and the ratio of their amplitudes is c . In the light of the above statements, choose the most appropriate answer from the options given
Options
- ABoth (A) and (R) are true and (R) is the correct explanation of (A)
- BBoth (A) and (R) are true but (R) is not the correct explanation of (A)
- C(A) is true but (R) is false
- D(A) is false but (R) is true
Correct answer
A. Both (A) and (R) are true and (R) is the correct explanation of (A)
Step-by-step solution
The instantaneous electric and magnetic fields in a plane electromagnetic wave are given by: E = E₀ (kx - t) B = B₀ (kx - t) Since the fields oscillate in phase, the sine terms are identical. The ratio of their instantaneous magnitudes is: E B = E₀ (kx - t) B₀ (kx - t) = E₀ B₀ Since the ratio of their amplitudes E₀ B₀ = c , the instantaneous ratio E B is also constant and equal to c . Thus, both (A) and (R) are true, and (R) is the correct explanation of (A). Answer: Both (A) and (R) are true and (R) is the correct