JEE Main202628 January 2026Evening ShiftPhysicsElectromagnetic WavesActual
A plane electromagnetic wave is moving in free space with velocity c=3 10⁸ ~m / s and its electric field is given as E =54 (k z- t) j ~V / m , where j is the unit vector along y -axis. The magnetic field vector B of the wave is:
Options
- A+1.8 10⁻⁷ (k z- t) i ~T
- B1.4 10⁻⁷ (k z- t) k ~T
- C-1.8 10⁻⁷ (k z- t) i ~T
- D1.4 10⁻⁷ (k z- t) i ~T
Correct answer
C. -1.8 10⁻⁷ (k z- t) i ~T
Step-by-step solution
For an electromagnetic wave, the relationship between electric and magnetic field amplitudes is B₀ = E₀ c . Here E₀ = 54 V/m and c = 3 10^8 m/s. So, B₀ = 54 3 10^8 = 1.8 10⁻⁷ T. The electric field is along the j direction. Since the wave travels in the +z direction, the magnetic field direction is determined by E B pointing in the +z direction. Using the right-hand rule: j (- i ) = k (positive z direction), confirming the magnetic field is in the - i direction. Therefore, B = -1.8 10⁻⁷ (kz - t) i T.