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The energy density associated with electric field E  and magnetic field B  of an electronmagnetic wave in free space is given by (  0 – permittivity of free space, μ 0 – permeability of free space)

1. U E = 0 2 2 E  , U B = 0 2 μ 2 B
2. U E = 2 E 2 0  , U B = 0 2 μ 2 B
3. U E = 2 E 2 0  , U B = 2 B μ 2 0
4. U E = 0 2 2 E  , U B = 2 B μ 2 0

Correct answer: U E = 2 E 2 0  , U B = 0 2 μ 2 B

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