The electric field of an electromagnetic wave in vacuum is proportional to cos(4x − ωt), where x is in metres. If ω = N×10⁸ rad/s, find N. Take c = 3×10⁸ m/s.

Question

G1 Physics · Accepted Answer

For a plane wave, wave speed v = ω/k. In vacuum, v = c = 3×10⁸ m/s. From the phase, k = 4 rad/m. Therefore, ω = ck = (3×10⁸)(4) = 12×10⁸ rad/s. Hence N = 12.