Practice question · Multiple choice
An antenna radiates into space. Which quantity describes how fast that energy crosses unit area?
Hints
- Its units are watts per square metre.
- It points along the direction of propagation for a plane wave.
Show the answer
A. The rate of energy flow per unit area carried by the field
Why
is the energy flux (power per unit area), pointing along the direction of wave travel. Energy density is a scalar volume density, while wave speed describes phase propagation rather than energy flux.
Practise Maxwell’s Equations and Electromagnetic Waves
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