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# Vacuums and Waves watch

1. (Original post by Hoofbeat)
See this is what I didn't know! I didn't know that electromagnetic fields exist in vacuums.

But (sorry I'm still pestering!) how does the energy manage to pass through the vacuum???!!! Sorry to be annoying!!!
because EM waves are waves of force, and forces can exist in vacuum (think opf the force between two electrons, or between two masses)
2. (Original post by Hoofbeat)
btw, regarding speed of light:

c = 1/sqrt(epsilon"0".mew"0")

where epsilon"0" = permitivitty of free space
mew"0" = permeability of free space
can someone show me the proof of this result,apparently in uses the vector product.
3. ∇ · E = 0
∇ · B = 0
∇ × E = -∂B/∂t
∇ × B = με ∂E/∂t

^^ These are Maxwell's equations in vacuo

=> ∇ × (∇ × E) = ∇(∇ · E) - ∇²E = ∇ × -∂B/∂t
=> ∇0 - ∇²E = -∂/∂t (∇ × B)
=> ∇²E = -∂/∂t (με ∂E/∂t)
=> ∇²E = με ∂²E/∂t²

=> c = 1/√με
4. (Original post by elpaw)
∇ · E = 0
∇ · B = 0
∇ × E = -∂B/∂t
∇ × B = με ∂E/∂t

^^ These are Maxwell's equations.

=> ∇ × (∇ × E) = ∇(∇ · E) - ∇²E = ∇ × -∂B/∂t
=> ∇0 - ∇²E = -∂/∂t (∇ × B)
=> ∇²E = -∂/∂t (με ∂E/∂t)
=> ∇²E = με ∂²E/∂t²

=> c = 1/√με
ok lemme get the symbols right:
B=Magnetic flux density
∇=?
t=time
5. (Original post by IntegralAnomaly)
ok lemme get the symbols right:
B=Magnetic flux density
∇=?
t=time
E is the electric field.

∇ is the del operator, i.e. the vector differential operator (∂/∂x i + ∂/∂y j + ∂/∂z k)
6. (Original post by elpaw)
E is the electric field.

∇ is the del operator, i.e. the vector differential operator (∂/∂x i + ∂/∂y j + ∂/∂z k)
what are u partially differentiating in the vector differential?
7. (Original post by IntegralAnomaly)
what are u partially differentiating in the vector differential?
the function that it operates on.

e.g. ∇Ø = ∂Ø/∂x i + ∂Ø/∂y j + ∂Ø/∂z k
8. (Original post by elpaw)
the function that it operates on.

e.g. ∇Ø = ∂Ø/∂x i + ∂Ø/∂y j + ∂Ø/∂z k
ahhhhh thanks

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