1. Magnetic field around electric current carrying conductor Jonathan Koh Chen Si Hao 4S2

2. 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

3. 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

4. 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

5. Experiment set-up

6. Observations 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

7. Observations 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?

8. Right hand grip rule (RHGR) Current flows from positive end of battery to the negative end

9. Magnetic field pattern Flat coil

10. 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

11. Magnetic field pattern Solenoid

12. Applet Applet ◦ http://micro.magnet.fsu.edu/electromag/java/c ompass/ http://micro.magnet.fsu.edu/electromag/java/c ompass/

13. 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)

14. Solenoid Increase magnetic field by: 1. Increase current 2. Increase number of turns per unit length 3. Placing a soft iron core within the solenoid

15. 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

16. 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.

17. Magnetic domains

18. Applets http://www.walter- fendt.de/ph14e/mfwire.htm http://www.walter- fendt.de/ph14e/mfwire.htm

19. Thank you