Answer: = ε_0 E 0 ²/2 = ε_0 E rms ².
- A <u> = ε_0 E<sub>0</sub>²/2 = ε_0 E<sub>rms</sub>²
- B <u> = ε_0 E<sub>0</sub>² in most textbook accounts
- C <u> = ε_0 E<sub>0</sub>²/4 during normal conditions
- D <u> = 2ε_0 E<sub>0</sub>² as generally observed
Correct answer: A. <u> = ε_0 E<sub>0</sub>²/2 = ε_0 E<sub>rms</sub>²
Explanation: Instantaneous u = ε_0 E² (total, including both E and B contributions). Time-averaged: <u> = ε_0 E<sub>rms</sub>² = ε_0 E<sub>0</sub>²/2. Intensity = <u> × c = ε_0 c E<sub>0</sub>²/2.
In an electromagnetic wave, the oscillating electric field (E) and magnetic field (B) are perpendicular to each other and to the direction the wave travels - a purely transverse wave that needs no medium, unlike sound.
Concept context
Maxwell's equations, EM spectrum, properties, and applications of each band.