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

[Doc Al]

Btw- Here says that B is external magnetic field, thus delta B is change of the external magnetic field. What is http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/fday.gif"

Yes, B is the external magnetic field. That page doesn't talk about delta B, since the field isn't changing. The loop moves in this case, so the flux through the loop changes. But it's the same idea as in all the other pages on this site: What matters is how the flux changes due to the external field. That determines the induced EMF and current in the loop.

 

[Doc Al]

So delta B in practical way, doesn't exists, right?

"Delta" just means change. It's just a way of describing how the field in the loop is changing. It's not a separate field.

 

[Physicsissuef]

"Delta" just means change. It's just a way of describing how the field in the loop is changing. It's not a separate field.

And in the http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/fday.gif" , there is delta B * delta A. In this case, delta B is the change of the field of the loop?

 

[Doc Al]

And in the http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/fday.gif" , there is delta B * delta A. In this case, delta B is the change of the field of the loop?

There's no delta B mentioned on this link. In http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/farlaw.html" there appears delta (B*A), which is the change in magnetic flux. In your link, only A changes so the change in flux = delta (B*A) = B*delta(A).

 

[Physicsissuef]

There's no delta B mentioned on this link. In http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/farlaw.html" there appears delta (B*A), which is the change in magnetic flux. In your link, only A changes so the change in flux = delta (B*A) = B*delta(A).

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).

 

[Doc Al]

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.

 

[Physicsissuef]

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?

 

[Doc Al]

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.

 

[Physicsissuef]

Yes. The rate at which the total flux is changing is greater in the first examples.

Ok, thank you very much.