Magnetic field around electric current carrying conductor
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Magnetic field around electric current carrying conductor. Jonathan Koh Chen Si Hao 4S2. A bit on history. In 1819, Hans Christian Oersted , a professor at the University of Copenhagen, accidentally discovered the magnetic effect of an electric current

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A bit on history
A bit on history

  • In 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 conductor
Electric current through a conductor

  • A magnetic field is produced when a current flows through a conductor

  • Different 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 p attern for straight wire
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


  • When 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


  • Magnetic field strength is larger when larger current flows through the circuit

  • When 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
Right hand grip rule (RHGR)

  • Current flows from positive end of battery to the negative end

Flat coil
Flat Coil

  • What 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


  • Applet



  • 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)


  • Increase magnetic field by:

  • Increase current

  • Increase number of turns per unit length

  • Placing a soft iron core within the solenoid


  • Theory of magnetism

  • If 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 domains
Magnetic domains

  • Everything is made up of atoms with electrons around the nucleus

  • Orbiting 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.