What is the net magnetic flux passing through a closed surface enclosing a bar manet?
The net magnetic flux passing through a closed surface enclosing a bar magnet is zero.
This is because magnetic field lines always form closed loops—they exit from the north pole of the magnet and enter the south pole, but for every field line that leaves the surface, another one enters it.
So, when you add up all the magnetic field lines going in and out of the closed surface, they cancel each other out, resulting in zero net flux.
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Imagine a bar magnet placed inside a closed surface—like a balloon or a box.
The magnetic field lines come out from the north pole of the magnet and enter back into the south pole. So, for every magnetic field line that leaves the surface, another one enters it somewhere else.
Because of this, the total number of lines going out is equal to the number coming in.
Since magnetic field lines always form closed loops and there are no "magnetic charges" (like magnetic monopoles) that can exist alone, the net magnetic flux through the entire closed surface adds up to zero.
This idea comes straight from Gauss's law for magnetism, which says:
∮ B · dA = 0 — meaning the total magnetic flux through any closed surface is always zero.
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So, when you have a bar magnet inside a closed surface, the magnetic field lines actually loop around from the north pole to the south pole.
Because of this, the number of magnetic lines going out of the surface is exactly balanced by the number coming back in.
That means if you add up all the magnetic flux passing through that surface, the total ends up being zero.
It’s kind of like water flowing in a loop—you can’t have more water leaving a closed container than entering it.
This happens because magnetic field lines always form closed loops, and there are no isolated magnetic charges (which would be like “sources” or “sinks” of magnetic field lines).
This fact is summed up in Gauss’s law for magnetism, which tells us the net magnetic flux through any closed surface is always zero.
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Okay, think of a bar magnet placed inside a closed surface, like a 3D bubble wrapped around it. Magnetic field lines always go out from the north pole and curve around to enter the south pole.
So inside that closed surface, the lines that come out of one side eventually go back in from the other.
Since the number of magnetic field lines leaving the surface equals the number entering it, they cancel each other out when calculating the total magnetic flux.
That’s why the net magnetic flux is zero.
It’s basically because there are no magnetic monopoles—no “only north” or “only south” pole that creates a one-way flow of field lines.
The magnetic field is always part of a loop. That’s why no matter how you place the magnet inside, as long as the surface is closed, the total flux through it will always add up to zero.
Okay, think of a bar magnet placed inside a closed surface, like a 3D bubble wrapped around it. Magnetic field lines always go out from the north pole and curve around to enter the south pole.So inside that closed surface, the lines that come out of one side eventually go back in from the other.
Since the number of magnetic field lines leaving the surface equals the number entering it, they cancel each other out when calculating the total magnetic flux.
That’s why the net magnetic flux is zero.
It’s basically because there are no magnetic monopoles—no “only north” or “only south” pole that creates a one-way flow of field lines.
The magnetic field is always part of a loop. That’s why no matter how you place the magnet inside, as long as the surface is closed, the total flux through it will always add up to zero.
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