# Formula for Magnetic field at a distance

Discussion in 'General Electronics Discussion' started by Muhammad Umair Khan, Mar 22, 2018.

12
0
Feb 20, 2018
How can i mathematically calculate (or represent) a magnetic field at any certain distance from a magnet or a solenoid?

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,482
2,830
Jan 21, 2010
Once you are far enough away, the intensity falls with the square of the distance.

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

12
0
Feb 20, 2018
What about a distance of 3 to 10 cm??? and how does the relation change with it?

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,482
2,830
Jan 21, 2010
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.

5. ### BobK

7,682
1,688
Jan 5, 2010
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

12
0
Feb 20, 2018
Thanks Bob, but could you put it in a mathematical equation please?

7. ### BobK

7,682
1,688
Jan 5, 2010
Look up dipole field on google.

Bob