for navigation Magnetism exists everywhere from tiny particles like electrons to the entire universe. Historically the word ‘magnetism’ was derived from iron ore magnetite (Fe O ). In olden days, magnets were used as magnetic compass for navigation, magnetic therapy for treatment and also used in magic shows. In modern days, many things we use in our daily life contain magnets (Figure .
). Motors, cycle dynamo, loudspeakers, magnetic tapes used in audio and video recording, mobile phones, head phones, CD, pen-drive, hard disc of laptop, refrigerator door, generator are a few examples. Earlier, both electricity and magnetism were thought to be two independent branches in physics. In , H.C.
Oersted observed the deflection of magnetic compass needle kept near a current carrying wire. This unified the two different branches, electricity and magnetism as a single subject ‘electromagnetism’ in physics. In this unit, basics of magnets and their properties are given. Later, how a current carrying conductor (here only steady current, not time-varying current is considered) behaves like a magnet is presented.
Figure . Uses of magnets in modern world – (a) speakers (b) head phones (c) MRI scan (d) Hard disc of laptop (a) (b) (c) (d) 12th - 12th - - - - - Unit Magnetism and magnetic effects of electric current . . Earth’s magnetic field and magnetic elements Figure .
Earth’s magnetic field Geographic South Pole Geographic North Pole Magnetic South Pole Magnetic North Pole From the activities performed in lower classes, you might have noticed that the needle in a magnetic compass or freely suspended magnet comes to rest in a position which is approximately along the geographical north- south direction of the Earth. The north pole of magnetic compass needle is attracted towards the magnetic south pole of the Earth which is near the geographic north pole (Figure . ). Similarly, the south pole of magnetic compass needle is attracted towards the magnetic north-pole of the Earth which is near the geographic south pole.
The branch of physics which deals with the Earth’s magnetic field is called