Procedure Place the bar magnet on the sheet of paper. Position the plotting compass at the end of magnet and draw dots on the paper at either end of the compass needle.
Reposition the compass as illustrated in Fig 20.2 and draw another dot at the arrowhead of the needle. Repeat this process until you reach the other pole of the magnet. Join the dots to show a field line. Repeat this from a number of different starting points so as to get a representation of the field.
Observation The shape of the magnetic fields are illustrated in Fig 20.3.
SN S Fig 20.2 Fig 20.3 N
SCIENCE,TECHNOLOGY & SOCIETY
Earth’s magnetic field The Earth has a magnetic field around it which behaves as though there were a giant bar magnet going through its centre. Obviously, there is no such bar magnet inside the Earth. It is believed that the magnetic field is due to the convection currents of molten iron in the Earth’s core.
The most obvious use of this magnetic field is for navigation by compass, but it has a far more important role. The Sun emits a huge amount of charged particles every second, called the solar wind.The Earth’s magnetic field protects us from this harmful solar wind which would otherwise be fatal. The field deflects the speeding particles toward Earth’s Poles. As the cosmic rays interact with the gases in the atmosphere they give off light.These are called the Northern Lights and the Southern Lights (see photo). Although we now need the field to protect us from the Sun’s radiation, without the mutating effects of this radiation evolution would not have occurred as it has on Earth, and we would not be here to wonder about it.
Fig 20.4: The Earth is protected from solar radiation by its magnetic field
Fig 20.5: The magnetic field around the Earth is similar to what you’d find if there were a giant bar magnet in its centre
Canada: a brilliant display of aurorae over the Yukon Territory. Such aurorae are caused by elec- trically charged particles of the solar wind colliding with gases in the Earth’s atmosphere.
