Electromagnetic Fields and Waves: How Energy Travels Outside the Wire
Maxwell's equations, plane waves, transmission lines, waveguides and antennas: the field picture behind every circuit and radio link.
Electromagnetic Fields and Waves · 50 questions
Try 3 questions
1. Maxwell's equation stating that the divergence of B is always zero expresses what physical fact?
- Magnetic fields cannot change in time
- Magnetic fields cannot pass through iron
- There are no isolated magnetic poles
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Answer: There are no isolated magnetic poles
Zero divergence means field lines never start or end, so every north pole comes paired with a south pole.
2. What is the curl of an electrostatic field, and what does that imply?
- Equal to the local current density
- Equal to the local charge density
- Zero, so the field is conservative
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Answer: Zero, so the field is conservative
With zero curl, the work done moving a charge between two points doesn't depend on the path, so a potential can be defined.
3. What does the divergence theorem relate?
- Gradients to a field's magnitude
- Line integrals to the area they enclose
- Outward flux to the sources enclosed inside
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Answer: Outward flux to the sources enclosed inside
The total flux leaving a closed surface equals the integral of the divergence, the 'source strength', over the volume inside.
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