12 Class Physics Chapter 5 - Statics Coaching Centre

Magnetism and Matter

Magnetic Properties of Materials

Ferromagnetic Materials: exhibit strong magnetic properties and can be easily magnetized. Examples include iron, cobalt, and nickel

Paramagnetic Materials: Display weak magnetic properties and are weakly attracted to a magnetic field. Examples include aluminum and platinum.

Diamagnetic Materials: exhibit very weak repulsion when placed in a magnetic field. Examples include copper and bismuth.

Magnetic Field Intensity (H)

Magnetic field intensity ( $H$ ) is a measure of the strength of a magnetic field in a material.

It is related to the magnetization ( $M$ ) of the material by the equation $H = B/μ ^{0} - M$ , where $B$ is the magnetic flux density and $μ_{0}$ is the permeability of free space.

Magnetic Susceptibility ( χ)

Magnetic susceptibility is a measure of how easily a material can be magnetized in the presence of an external magnetic field.

It is defined as $χ = M$ , where $M$ is the magnetization and $H$ is the magnetic field intensity.

Magnetic Dipole

A magnetic dipole is a pair of opposite magnetic charges (north and south poles) separated by a small distance.

Magnetic dipoles are found in elementary particles and also in macroscopic objects like magnets.

Magnetic Field Lines in a Bar Magnet

Magnetic field lines emerge from the north pole and enter the south pole in a bar magnet.

The field lines form closed loops and do not intersect.

Magnetic Field Inside and Outside a Bar Magnet

Inside a magnet, the magnetic field lines run from the south pole to the north pole.

Outside the magnet, the field lines follow a north-to-south direction.

Magnetic Field due to a Magnetic Dipole

The magnetic field at a point on the axial line of a magnetic dipole is given by $B_{axial} = μ ^{0} 2 m/4πr ^{3}$ , where $m$ is the magnetic moment of the dipole and $r$ is the distance from the dipole.

Bar Magnet as an Equivalent Solenoid

A bar magnet can be considered as equivalent to a solenoid when viewed from a distance.

The north pole of the bar magnet corresponds to the end from which field lines emerge in the equivalent solenoid.

Torque on a Magnetic Dipole in a Uniform Magnetic Field

A magnetic dipole experiences a torque ( $τ$ ) when placed in a uniform magnetic field ( $B$ ).

The torque is given by $τ = m \times B$ , where $m$ is the magnetic moment of the dipole.

Para-, Dia-, and Ferromagnetism

Paramagnetism: Materials with unpaired electrons that align with an external magnetic field.

Diamagnetism: Materials with all paired electrons that slightly repel from an external magnetic field.

Ferromagnetism: Materials with a spontaneous alignment of magnetic dipoles, resulting in strong magnetization.

Curie Temperature

The Curie temperature is the temperature at which a ferromagnetic or ferrimagnetic material loses its magnetic properties.

Above this temperature, thermal agitation disrupts the alignment of magnetic domains.