Why a magnetic flux in closed surface area is always 0?

In summary, the magnetic flux through a closed surface is always zero due to the fact that magnetic monopoles do not exist. This is one of Maxwell's equations and is in contrast to Gauss's law for electric fields. In the case of stationary fields, the magnetic flux is definitely zero. Even in the case of non-stationary fields, the flux remains zero due to the same principle. This can be visualized by understanding that magnetic flux lines form closed loops, and thus the number of lines entering a closed surface must equal the number exiting, resulting in a net flux of zero. This is not related to the Faraday cage, which works by cancelling the electric field inside the cage through the realignment of charges.
  • #36
Physicsissuef said:
And can I ask you why on the 1-st example there is so much bigger voltage (-16 volts), and in the example below (-0,004 volts)? What is the difference? In the first example there are two coils (it is actually transformator).
The first example is not a transformer, it's just two coils. The only difference between them is the number of turns.

The two examples are different! The induced EMF depends on the rate at which the flux changes, which is different in each case. All the values needed to calculate the induced EMF (and the formula to use) are given. Just plug in the numbers.
 
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  • #37
Doc Al said:
The first example is not a transformer, it's just two coils. The only difference between them is the number of turns.

The two examples are different! The induced EMF depends on the rate at which the flux changes, which is different in each case. All the values needed to calculate the induced EMF (and the formula to use) are given. Just plug in the numbers.
In the first case, the flux is changing faster, than the example below?
 
  • #38
Physicsissuef said:
In the first case, the flux is changing faster, than the example below?
Yes. The rate at which the total flux is changing is greater in the first examples.
 
  • #39
Doc Al said:
Yes. The rate at which the total flux is changing is greater in the first examples.

Ok, thank you very much.
 

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