ch 5- Magnetism and matter

properties of magnetic field lines

never intersect

form continuous closed loops

tangent to field lines give direction of magnetic field

greater the number of field lines greater the value of magnetic field

Gauss’s law in magnetism

Gauss’s law in magnetism states that surface integral of magnetic flux over a closed surface is 0. This proves that magnetic dipoles do not exist.

diamagnetic substance

substance which exhibit weak force of repulsion from a magnet

ex- Sb, Bi, Ag, Cu, Pb, Hg, alcohol, water, NaCl, air, H2, Si, N, quartz

properties of diamagnetic substance

• do not possess permanent dipole moment

• independent of temperature

• susceptibility- small and -ve

• relative permeability<1

• when freely suspended in a magnetic field it sets itself at a right angle to the direction of magnetic field

• in non uniform magnetic field it tends to move from region with stronger field to region with weaker field

paramagnetic substance

substance that experience weak attraction towards magnet.

non-zero magnetic moment

Ex- Al,Na,CuCl₂,liquid oxygen, Ca

Meissner effect

phenomenon of perfect diamagnetism in superconductors

properties of paramagnetic substance

• When freely suspended in magnetic field it alligns itself in the direction of the field

• In non-uniform magnetic field it goes from region with weaker field to region with stronger field

• relative permeability>1

• susceptibility small and +ve

• susceptibility is inversely proportional to temperature

Ferromagnetic substance

substances which experience a very strong attraction towards magnet

Ex- Alinico, Steel, Fe, Co, Ni

hard ferromagnetic substance

substance which presist magnetism when external field is removed

ex-Alinico (Alloy of Al, Ni, Co, Cu, Fe), steel

soft ferromagnetic substance

substance in which magnetism disappears when external field is removed.

ex-Co, Ni, Fe

Why is hard ferromagnetic substance used as permenant magnets

because the magnetism in hard ferromagnetic substances presist even after the external field is removed.

properties of ferromagnetic substance

• relative permeability very large value

• susceptibility +ve and very large value

• When freely suspended in magnetic field it alligns itself to the direction of the field

• in non uniform magnetic field, it moves form region of weaker field to a region with stronger field

• on rising temp susceptibility decreases until it reaches a point call curie point at which the substance loses its ferromagnetic property and attains paramagnetic behavior

magnetic intensity

field that is produced inside a solenoid when current is passed through it

H=nI , n=no. of turns in solenoid per unit length

unit- Am^-1

magnetisation

ratio of magnetic moment per unit volume

M=m/V

unit- Am^-1

susceptibility

ratio of magnetisation to magnetic intensity

M/H

no unit

relative permeability

ratio of permeability in a medium by permeability in free space