Answer: I ∝ 1/r² (inverse square law).
- A I ∝ 1/r² (inverse square law)
- B I ∝ 1/r, falling off linearly rather than quadratically
- C I ∝ r², growing instead of shrinking with distance
- D I stays exactly constant regardless of distance from the source
Correct answer: A. I ∝ 1/r² (inverse square law)
Explanation: Power spreads over a sphere: I = P/(4πr²). As r doubles, area quadruples, I decreases 4 times. This inverse square law applies to all EM radiation from point sources.
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.