The electric field in an electromagnetic wave is given by E⃗=î 40 cos ω(t-z / c) NC⁻¹. The magnetic field induction of this wave is (in SI unit) :

Solution

Physics sir · 4 steps

Fix the direction with E × B pointing along the travel direction, then get the size from B = E/c.

1. Direction of travel. The phase is ω(t - z/c), so the wave moves along +z. The electric field points along î.
2. Direction of B. In an EM wave, E⃗ × B⃗ points along the direction of travel. Since î × ĵ = k̂, the magnetic field must point along ĵ.

   B₀ = E₀/c = 40/c T

3. Same phase. E⃗ and B⃗ oscillate in phase, so B⃗ keeps the same factor cos ω(t - z/c).
4. So. B⃗ = ĵ 40/c cos ω(t - z/c), which is option (a).

The idea to keep. In any EM wave, E, B and the direction of travel are mutually perpendicular, with E × B along the travel direction. The sizes are linked by B₀ = E₀/c.

Answer from the NTA final answer key. Solution by PrepWiser.