PRAVEEN: June 2012

Saturday 30 June 2012

MAGNETIC BEHAVIOUR OF A CURENT CARRYING SOLENOID

A solenoid is a long helix having a large number of close turns of insulated copper wire wound over a tube or china-clay. When an electric current is passed through the solenoid, it behaves like a bar magnet.

its verified by:

1. A current-carrying solenoid suspended freely always rests in a definite direction.

If we place a solenoid in a brass hook and suspend it by along thread so that it can move freely in a horizontal plane, we find that it always rest in the north-south direction. The end of the solenoid pointing north is called the north pole and the end of the solenoid pointing south is called south pole.

2. Two current-carrying solenoids exhibit mutual attraction and repulsion.

If we suspend a solenoid in a brass-hook by means of a thread and bring one by one the end of another solenoid close to one end of the suspended solenoid, we observe that when the south pole of the second solenoid brought near the north pole of the suspended solenoid, the suspended solenoid comes closer, but when the north pole is brought near the north pole, the suspended solenoid moves away. This shows that the unlike poles of the two solenoids attract each other and like poles repel each other.

The above observation shows that a current-carrying solenoid is just like a bar-magnet, having north pole and south pole.

posted by

praveen

please give comment about it.....

Friday 29 June 2012

MAGNETIC CLASSIFICATION OF SUBSTANCES

1.Para magnetic substances

2.Dia magnetic substances

3.Ferro magnetic substances

PARA MAGNETIC SUBSTANCES

para magnatic substances feebly magnetice in the direction of magnetising field.

It attracts towards the magnet when brought close to the pole of a powerfull magnet.

Magnetisation M is weak but in same direction of magnetising field.

It have small positive susceptivity.

Relative permiability is slightly greater than 1.

Alluminium,sodium,platinum,manganeese....

DIA MAGNETIC SUBSTANCES

dia magnetic substances feebly magnetice opposite to the direction of magnetising field.

They reppel away from a magnet when brought close to a powerfull magnet.

Magnetisation M is weak directed opposite to the magnetic field.

The susceptivity of dia magnetic substances is small and negative

Relative permiablity is slightly less than 1.

Bismuth,zinc,copper,silver,gold.

FERRO MAGNETIC SUBSTANCES

ferro magnetic substances strongly magnetice in the direction of magnetising field.

Fastly attracted towards magnet.

Magnetisation M is strong and same direction as the magnetising field.

The susceptivity of ferro magnetic substances is large positive value.

Relative permiablity is the order of 100's and 1000's.

by praveen........

if you like it..please comment.

Wednesday 27 June 2012

ELECTRIC CELL AND EMF

A source of electric energy

EMF-electromotive force:-

It is the workdone by a cell in forcing a unit positive charge to flow through the whole circuit.

EMF (E)=dw/dq

UNIT OF EMF is volt(V)

*A battery of emf ${\cal E}$ and internal resistance connected to a load resistor of resistance .*
$\begin{figure} \epsfysize =2.5in \centerline{\epsffile{circuit1.eps}} \end{figure}$

INTERNAL RESISTANCE(r)

It is the resistance offered by the electrolite of the cell to the flow of current through it.

1.it is directly propotional to the seperation between the two plates.

2.it is inversly propotional to the plates area dipped in electrolite.

3.it depends upon nature,concentration,temperature of the electrolite.

so it increases with increase in concentration.

EQUATION

pottential difference=V

EMF=E

current=i

Internal resistance=r

V=E-i*r

r=(E-V)/i [i=V/R]

r=(E-V)/(V/R)

then

r=R(E/V-1) i=E-V/r

E=v+i*r [V=ir]

E=iR+ir

taking 'i' as common;

E=i(R+r)

i=E/(R+r)

V=E-ir

E=V+ir

E=iR+ir

E=i(R+r)

THEN

i=E/(R+r)

by praveen........
if you like it..please comment.

Sunday 17 June 2012

si units

$\ \Iota$	Electric current	ampere (SI base unit)	$\mathrm{A=C\ s^{-1}}$
$\ Q$	Electric charge	coulomb	$\mathrm{C=A\ s}$
$U,\ \Delta V,\ \Delta\phi,\ \Epsilon$	Potential difference; Electromotive force	volt	$\mathrm{V=J\ C^{-1}=kg\ A^{-1}m^2s^{-3}}$
$R;\ \Zeta;\ \Chi$	Electric resistance; Impedance; Reactance	ohm	$\mathrm{\Omega=V\ A^{-1}=kg\ m^{2} \ A^{-2}s^{-3}}$
$\ \rho$	Resistivity	ohm metre	$\mathrm{\Omega\ m=kg\ A^{-2}m^3s^{-3}}$
$\ \Rho$	Electric power	watt	$\mathrm{W=V\ A=kg\ m^2s^{-3}}$
$\ C$	Capacitance	farad	$\mathrm{F=C\ V^{-1}=A^2kg^{-1}m^{-2}s^4}$
$\mathbf{\Epsilon}$	Electric field strength	volt per metre	$\mathrm{V\ m^{-1}=C^{-1}N=kg\ A^{-1}m\ s^{-3}}$
$\mathbf{D}$	Electric displacement field	Coulomb per square metre	$\mathrm{C\ m^{-2}=A\ m^{-2}s}$
$\varepsilon$	Permittivity	farad per metre	$\mathrm{F\ m^{-1}=A^{2}kg^{-1}m^{-3}s^{4}}$
$\!\chi_e$	Electric susceptibility	Dimensionless
$\Beta;\ G;\ \Upsilon$	Conductance; Admittance; Susceptance	siemens	$\ \mathrm{S=\Omega^{-1}=kg^{-1}A^2m^{-2}s^3}$
$\gamma,\ \kappa,\ \sigma$	Conductivity	siemens per metre	$\mathrm{S\ m^{-1}=A^2kg^{-1}m^{-3}s^3}$
$\ \mathbf{B}$	Magnetic flux density, Magnetic induction	tesla	$\mathrm{T=Wb\ m^{-2}=kg\ A^{-1}s^{-2}}$
$\ \Phi$	Magnetic flux	weber	$\mathrm{Wb=V\ s=kg\ A^{-1}m^2s^{-2}}$
$\mathbf{H}$	Magnetic field strength	ampere per metre	$\mathrm{A\ m^{-1}}$
$L,\ \Mu$	Inductance	henry	$\mathrm{H=Wb\ A^{-1}=V\ A^{-1}s=kg\ A^{-2}m^2s^{-2}}$
$\ \mu$	Permeability	henry per metre	$\mathrm{H m^{-1}=kg\ A^{-2}m\ s^{-2}}$
$\ \chi$	Magnetic susceptibility	Dimensionless

MAGNETISM

Magnetism

Magnetism is a property of materials that respond to an applied magnetic field. Permanent magnets have persistent magnetic fields caused by ferromagnetism. That is the strongest and most familiar type of magnetism. However, all materials are influenced varyingly by the presence of a magnetic field. Some are attracted to a magnetic field (paramagnetism); others are repulsed by a magnetic field (diamagnetism); others have a much more complex relationship with an applied magnetic field (spin glass behavior and antiferromagnetism). Substances that are negligibly affected by magnetic fields are known as non-magnetic substances. They include copper, aluminium, gases, and plastic. Pure oxygen exhibits magnetic properties when cooled to a liquid state.

An understanding of the relationship between electricity and magnetism began in 1819 with work by Hans Christian Oersted, a professor at the University of Copenhagen, who discovered more or less by accident that an electric current could influence a compass needle. This landmark experiment is known as Oersted's Experiment. Several other experiments followed, with André-Marie Ampère, who in 1820 discovered that the magnetic field circulating in a closed-path was related to the current flowing through the perimeter of the path; Carl Friedrich Gauss; Jean-Baptiste Biot and Félix Savart, both of which in 1820 came up with the Biot-Savart Law giving an equation for the magnetic field from a current-carrying wire; Michael Faraday, who in 1831 found that a time-varying magnetic flux through a loop of wire induced a voltage, and others finding further links between magnetism and electricity. James Clerk Maxwell synthesized and expanded these insights into Maxwell's equations, unifying electricity, magnetism, and optics into the field of electromagnetism. In 1905, Einstein used these laws in motivating his theory of special relativity,^[6] requiring that the laws held true in all inertial reference frames.

SOURCE

Electric currents or more generally, moving electric charges create magnetic fields (see Maxwell's Equations).
Many particles have nonzero "intrinsic" (or "spin") magnetic moments. Just as each particle, by its nature, has a certain mass and charge, each has a certain magnetic moment, possibly zero.

It was found hundreds of years ago that certain materials have a tendency to orient in a particular direction. For example ancient people knew that "lodestones," when suspended from a string and allowed to freely rotate, come to rest horizontally in the North-South direction. Ancient Mariners used lodestones for navigational purposes.
In magnetic materials, sources of magnetization are the electrons' orbital angular motion around the nucleus, and the electrons' intrinsic magnetic moment (see electron magnetic dipole moment). The other sources of magnetism are the nuclear magnetic moments of the nuclei in the material which are typically thousands of times smaller than the electrons' magnetic moments, so they are negligible in the context of the magnetization of materials. Nuclear magnetic moments are important in other contexts, particularly in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI).
Ordinarily, the enormous number of electrons in a material are arranged such that their magnetic moments (both orbital and intrinsic) cancel out. This is due, to some extent, to electrons combining into pairs with opposite intrinsic magnetic moments as a result of the Pauli exclusion principle (see electron configuration), or combining into filled subshells with zero net orbital motion. In both cases, the electron arrangement is so as to exactly cancel the magnetic moments from each electron. Moreover, even when the electron configuration is such that there are unpaired electrons and/or non-filled subshells, it is often the case that the various electrons in the solid will contribute magnetic moments that point in different, random directions, so that the material will not be magnetic.

Diamagnetism

Diamagnetism appears in all materials, and is the tendency of a material to oppose an applied magnetic field, and therefore, to be repelled by a magnetic field. However, in a material with paramagnetic properties (that is, with a tendency to enhance an external magnetic field), the paramagnetic behavior dominates.^[8] Thus, despite its universal occurrence, diamagnetic behavior is observed only in a purely diamagnetic material. In a diamagnetic material, there are no unpaired electrons, so the intrinsic electron magnetic moments cannot produce any bulk effect.

paramagnetism

In a paramagnetic material there are unpaired electrons, i.e. atomic or molecular orbitals with exactly one electron in them. While paired electrons are required by the Pauli exclusion principle to have their intrinsic ('spin') magnetic moments pointing in opposite directions, causing their magnetic fields to cancel out, an unpaired electron is free to align its magnetic moment in any direction. When an external magnetic field is applied, these magnetic moments will tend to align themselves in the same direction as the applied field, thus reinforcing it.

ferromagnetism

A ferromagnet, like a paramagnetic substance, has unpaired electrons. However, in addition to the electrons' intrinsic magnetic moment's tendency to be parallel to an applied field, there is also in these materials a tendency for these magnetic moments to orient parallel to each other to maintain a lowered-energy state. Thus, even when the applied field is removed, the electrons in the material maintain a parallel orientation.