# Formula for Magnetic field at a distance

Feb 20, 2018
12
How can i mathematically calculate (or represent) a magnetic field at any certain distance from a magnet or a solenoid?

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,509
Once you are far enough away, the intensity falls with the square of the distance.

This doesn't work when you're really close.

Feb 20, 2018
12
Once you are far enough away, the intensity falls with the square of the distance.

This doesn't work when you're really close.

What about a distance of 3 to 10 cm??? and how does the relation change with it?

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,509
What about a distance of 3 to 10 cm??? and how does the relation change with it?

It depends. If the magnet (or solenoid) is only a couple of mm in size, then yes. If it's a 20cm cube, then no.

#### BobK

Jan 5, 2010
7,682
Once you are far enough away, the intensity falls with the square of the distance.
Unless you have found a magnetic monopole, it falls off as the cube of the distance (field of a dipole.)

Near one pole, or near a long straight piece of wire carrying a current, it would be inverse square.

Bob

Feb 20, 2018
12
Unless you have found a magnetic monopole, it falls off as the cube of the distance (field of a dipole.)

Near one pole, or near a long straight piece of wire carrying a current, it would be inverse square.

Bob

Thanks Bob, but could you put it in a mathematical equation please?

#### BobK

Jan 5, 2010
7,682
Look up dipole field on google.

Bob

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