An electromagnetic wave travels through free space in the +x direction. At a particular point and instant, its magnetic field is B = 2×10⁻⁷ĵ T. What is the corresponding electric-field vector at that point?
Options

Question

An electromagnetic wave travels through free space in the +x direction. At a particular point and instant, its magnetic field is B = 2×10⁻⁷ĵ T. What is the corresponding electric-field vector at that point?

Options

G1 Physics · Accepted Answer

For a plane electromagnetic wave in free space, E = cB in magnitude. Therefore, E = 3×10⁸ × 2×10⁻⁷ = 60 V·m⁻¹. For the direction, the propagation direction is given by E×B. The wave travels along +î and B is along +ĵ. We need E such that E×ĵ = î. Since (-k̂)×ĵ = î, the electric field points along -k̂. Thus, E = -60k̂ V·m⁻¹. Correct option: B.