Correct Answer - Option 4 : inversely proportional to square of the r
Magnetic field strength (B):
- Magnetic field strength refers to the ratio of the MMF which is required to create a certain Flux Density within a certain material per unit length of that material. Some experts also call is as the magnetic field intensity.
- Furthermore, magnetic flux refers to the total number of magnetic field lines that penetrate an area. Furthermore, the magnetic flux density tends to diminish with increasing distance from a straight current-carrying wire or a straight line that connects a pair of magnetic poles around which the magnetic field is stable.
- Magnetic field strength refers to a physical quantity that is used as one of the basic measures of the intensity of the magnetic field. The unit of magnetic field strength happens to be ampere per meter or A/m.
- As the distance of a point from the magnet increases the magnetic flux density decreases and the magnetic field intensity decreases.
The magnetic intensity due to an isolated pole of strength mp at a distance (r) is:
\(B=\frac{\mu_om_p}{4\pi r^2}\)
Hence option (4) is the correct answer.
