| 1. Maxwell's equations in vacuum (contd..) |
| Gauss's law: enclosed charges |
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Integrate over a closed volume: |
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(5) |
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Use a mathematical identity (Gauss's theorem) |
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(6) |
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Relationship between electric field on a closed surface and the
charge enclosed inside it
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The part in red: source of the electric field |
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Leads to Coulomb's law if Q is a point charge at the centre of  ,
a sphere of radius r : |
