Physics · Class 11 Science
Ch 12Magnetism — Class 11 Physics, concept-first.
Magnetism as a phenomenon has been known since before 600 B.C. (lodestone, magnetite, attracting iron), but it was only put on a systematic scientific footing much later.
Key concepts
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Magnetic Field of a Bar Magnet
For a point far from a bar magnet (), the field can be found by analogy with the electric dipole. On the AXIS, at distance from the centre, , directed along ; on the perpendicular bisector (the EQUATOR), , directed oppos…
Most relevant Q&A
- Let $r$ be the distance of a point on the axis of a bar magnet from its centre. The magnetic field at $r$ is always proportional to (A) $1/r…Free
- A magnetic pole of a bar magnet with pole strength of 100 A m is 20 cm away from the centre of a bar magnet. The bar magnet has pole strengt…Free
- Two small and similar bar magnets have magnetic dipole moment of 1.0 A m$^2$ each. They are kept in a plane in such a way that their axes ar…Preview
In previous exams
How often this chapter’s concepts have been examined — real appearance data, never estimated.
Chapter contents
The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.
Introduction
Magnetism as a phenomenon has been known since before 600 B.C. (lodestone, magnetite, attracting iron), but it was only put on a systematic scientific footing much later.
Magnetic Lines of Force and Magnetic Field
Just as electrostatics uses electric lines of force to visualise the electric field due to charges, magnetism uses magnetic lines of force to visualise the magnetic field due to a magnet.
The Bar Magnet
A bar magnet is modelled as carrying a north pole of pole strength and a south pole of pole strength , with the two poles separated inside the magnet by a distance .
Magnetic Field due to a Bar Magnet at a Point along its Axis and at a Point along its Equator
Consider a bar magnet of magnetic dipole length and magnetic dipole moment , and let be a point along its axis at distance from the centre of the dipole, with , so that and .
Magnetic Field due to a Bar Magnet at an Arbitrary Point
The axial and equatorial formulas of the previous section only apply to points lying exactly on the magnet's axis or exactly on its equatorial plane.
Gauss' Law of Magnetism
Gauss' law of electrostatics states that the net electric flux through any closed (Gaussian) surface is proportional to the net electric charge enclosed by that surface.
Earth's Magnetism
It is common everyday experience that a bar magnet or magnetic needle, suspended freely in air, always aligns itself along the geographic North-South direction; and if it additionally has the freedom…
More questions
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- Q1Let $r$ be the distance of a point on the axis of a bar magnet from its centre. The magnetic field at $r$ is always proportional to (A) $1/r…Free
- Q2Magnetic meridian is the plane (A) perpendicular to the magnetic axis of Earth (B) perpendicular to geographic axis of Earth (C) passing thr…Free
- Q3The horizontal and vertical components of magnetic field of Earth are the same at some place on the surface of Earth. The magnetic dip angle…Free
- Q4Inside a bar magnet, the magnetic field lines (A) are not present (B) are parallel to the cross-sectional area of the magnet (C) are in the…Preview
- Q5A place where the vertical component of Earth's magnetic field is zero has the angle of dip equal to (A) $0^\circ$ (B) $45^\circ$ (C) $60^\c…Preview
- Q6A place where the horizontal component of Earth's magnetic field is zero lies at (A) geographic equator (B) geomagnetic equator (C) one of t…Preview
- Q7A magnetic needle kept nonparallel to the magnetic field in a nonuniform magnetic field experiences (A) a force but not a torque (B) a torqu…Preview
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- Q13A magnetic pole of a bar magnet with pole strength of 100 A m is 20 cm away from the centre of a bar magnet. The bar magnet has pole strengt…Free
- Q14A magnet makes an angle of $45^\circ$ with the horizontal in a plane making an angle of $30^\circ$ with the magnetic meridian. Find the true…Free
- Q15Two small and similar bar magnets have magnetic dipole moment of 1.0 A m$^2$ each. They are kept in a plane in such a way that their axes ar…Preview
- Q16A circular magnet is made with its north pole at the centre, separated from the surrounding circular south pole by an air gap. Draw the magn…Preview
- Q17Two bar magnets are placed on a straight line with their north poles facing each other on a horizontal surface. Draw the magnetic lines of f…Preview