Magnetic field around electric current carrying conductorJonathan KohChen Si Hao4S2

A bit on historyIn 1819, Hans Christian Oersted, a

professor at the University of Copenhagen, accidentally discovered the magnetic effect of an electric current

While demonstrating the heating effect of current to his students, he noticed that a compass needle nearby was deflected when the current was switched on.

Led to discovery of electromagnetism

Electric current through a conductorA magnetic field is produced when a

current flows through a conductorDifferent magnetic field patterns are

set up due to different dimensions of the conductor

Direction of the magnetic field is based on the direction of the current in the circuit

Experiment (Magnetic field pattern for straight wire)

Place a wire upward through a small hole in a horizontal cardboard

A fine layer of iron filings is then sprinkled on the cardboard

The current is switched on and the card tapped gently

The filings set in a series of concentric circles about the wire as the centre

Experiment set-up

ObservationsWhen iron filings are sprinkled around

a conducting wire, the iron filings are pulled to form concentric circles around the wire

The distance in between the circles increases at an increasing rate – Magnetic fields strength is stronger nearer the wire

ObservationsMagnetic field strength is larger when

larger current flows through the circuitWhen direction of current is reversed,

the north pointer of the compass switches to the position of the south pointer

Concentric circles of iron fillings remains

So how to find direction of magnetic field?

Right hand grip rule (RHGR)

Current flows from positive end of battery to the negative end

Magnetic field patternFlat coil

Flat CoilWhat happens at the centre of the

coil?The fields due to the sides of the coils

are in the same direction and they combine to give a strong magnetic field

Magnetic field patternSolenoid

AppletApplet

◦http://micro.magnet.fsu.edu/electromag/java/compass/

Solenoid

Increases the number of turns of a flat coil makes it a solenoid

Magnetic field pattern resembles that of a bar magnet

The end that current is flowing towards through the solenoid is the N pole (RHGR)

Solenoid

Increase magnetic field by:1. Increase current2. Increase number of turns per unit

length3. Placing a soft iron core within

the solenoid

Solenoid

Theory of magnetismIf we take a bar magnet

and cut it into two pieces, each piece becomes a magnet itself with a N pole and a S pole

Magnetic domainsEverything is made up of atoms

with electrons around the nucleusOrbiting motion of electrons in

sets up a magnetic dipole causing each atom to become a atomic magnet

A group of atomic magnets pointing in the same direction is called a magnetic domain.

Magnetic domains

Appletshttp://www.walter-fendt.de/ph14e

/mfwire.htm

Thank you