Neutral Point of Magnet - Magnetism and Matter Class 12 Physics Notes
A neutral point is a location where the magnetic field of a bar magnet exactly cancels Earth’s horizontal magnetic field, resulting in zero net magnetic field; its position depends on the magnet’s orientation and can lie on either the axial or equatorial line.
Table of Contents
eSaral › JEE › JEE Main ›Neutral Point of Magnet
🚀 Checkout eSaral Courses
A neutral point of Magnet is a point at which the resultant magnetic field is zero. In general, the neutral point is obtained when a horizontal component of the earth's field is balanced by the produced by the magnet. When the N pole of the magnet points South and the magnet in the magnetic meridian. When we plot the magnetic field of a bar magnet the curves obtained represent the superposition of magnetic fields due to bar magnet and earth.
India's Best Exam Preparation for Class 12th - Download Now
DEFINITION
A neutral point in the magnetic field of a bar magnet is that point where the field due to the magnet is completely neutralized by the horizontal component of the earth's magnetic field. At neutral point field due to bar magnet (B) is equal and opposite to horizontal component of earth's magnetic field $\left( B _{ H }\right) or \quad B = B _{ H }$
-
The neutral point when the north pole of a magnet is towards the geographical north of the earth.
The neutral points $N_{1}$ and $N_{2}$ lie on the equatorial line. The magnetic field due to magnet at a neutral point is
India's Best Exam Preparation for Class 12th - Download Now
$B =\frac{\mu_{0}}{4 \pi} \frac{ M }{\left( r ^{2}+\ell^{2}\right)^{\frac{3}{2}}}$
Where M is the magnetic dipole moment of the magnet, $2 l$is its length, and r is a distance of the neutral point.
At neutral point $B = B _{ H } \cdot \quad$ so $\quad \frac{\mu_{0}}{4 \pi} \frac{ M }{\left( r ^{2}+\ell^{2}\right)^{\frac{3}{2}}}= B _{ H }$
For a small bar magnet $\left(\ell^{2}<< r ^{2}\right)$ then $\frac{\mu_{0}}{4 \pi} \frac{ M }{ r ^{3}}= B _{ H }$
-
Neutral point when south pole of a magnet is towards geographical north of earth.
The neutral points $N_{1}$ and $N_{2}$ lie on the axial line of magnet. The magnetic field due to magnet
at neutral point is $B =\frac{\mu_{0}}{4 \pi} \frac{2 Mr }{\left( r ^{2}-\ell^{2}\right)^{2}}$
At neutral point $B =\frac{\mu_{0}}{4 \pi} \frac{2 Mr }{\left( r ^{2}-\ell^{2}\right)^{2}}$ so $\frac{\mu_{0}}{4 \pi} \frac{2 Mr }{\left( r ^{2}-\ell^{2}\right)^{2}}= B _{ H }$
For a small bar magnet $\left(\ell^{2}<< r ^{2}\right)$ then $\frac{\mu_{0}}{4 \pi} \frac{2 M }{ r ^{3}}= B _{ H }$
India's Best Exam Preparation for Class 12th - Download Now
Special Point
When a magnet is placed with its S pole towards north of earth neutral points lie on its axial line. If magnet is placed with its N pole towards north of earth neutral points lie on its equatorial line. So neutral points are displaced by $90^{\circ}$ on rotating magnet through $180^{\circ}$ In general if magnet is rotated by angle $\theta$ neutral point turn through an angle $\frac{\theta}{2}$
Neutral Point in Special Cases
(a) If two bar magnets are placed with their axis parallel to each other and their opposite poles face each other then there is only one neutral point (x) on the perpendicular bisector of the axis equidistant from the two magnets.
(b) If two bar magnets are placed with their axis parallel to each other and their like poles face each other then there are two neutral points on a line equidistant from the axis of the magnets.
Also Read: Properties of Paramagnetic & Diamagnetic Materials
Frequently Asked Questions
Find answers to common questions.
What is the neutral point of a magnet?
The neutral point of a magnet is the point in the combined magnetic field of a bar magnet and Earth where the net magnetic field is zero. At this point, the field due to the magnet is equal in magnitude and exactly opposite in direction to the horizontal component of Earth's magnetic field, B_H, so they cancel each other out completely.
Where do neutral points lie when the north pole of a magnet faces geographic north?
When the north pole faces geographic north, the neutral points lie on the equatorial line (perpendicular bisector of the magnetic axis). The equatorial field of the magnet points southward — opposite to B_H — so cancellation is possible only at these two symmetric equatorial positions on either side of the magnet.
Where do neutral points lie when the south pole of a magnet faces geographic north?
When the south pole faces geographic north, the neutral points lie on the axial line of the magnet. The axial field at these positions points in the geographic south direction — opposing B_H — so the two fields cancel. There are two symmetric neutral points, one on each side along the axis.
What is the formula for finding the distance of the neutral point from a short bar magnet?
For a short bar magnet when N-pole faces north (equatorial case): μ₀M / (4πr³) = B_H, giving r = ∛(μ₀M / 4πB_H). When S-pole faces north (axial case): μ₀(2M) / (4πr³) = B_H, giving r = ∛(μ₀ × 2M / 4πB_H). The axial neutral point is therefore farther from the magnet than the equatorial one for the same magnet.
What happens to neutral points when a magnet is rotated by angle θ?
When the magnet is rotated by an angle θ, the neutral points rotate by θ/2. This means rotating the magnet by 180° shifts the neutral points by 90° — from the equatorial line to the axial line (or vice versa). This general rule is directly applicable in JEE Main and JEE Advanced rotation-based problems.