Magnets and magnetic field lines
What is a Magnet?
A magnet is a material that attracts pieces of iron, nickel or other magnetic materials. Magnets have magnetic field lines around them which form closed loop. Magnets attract or repel any magnetic material with the help of magnetic field lines. Magnetic field lines of magnet are like our hand. As we can push, pull and lift something with our hands similarly magnets can also attract or repel using magnetic field lines. All magnets have two poles, North pole and South pole. Magnetic field lines comes out from the north pole and enter the magnet from south pole. There are different shapes of magnet. Horseshoe magnet (U shape), cylindrical magnet, dumbbell magnet, etc.
Properties of magnetic field lines:
Two magnetic field lines never cross each other. Because each point on the magnetic field has only one direction. If the magnetic field lines cross each other at any point it means that point has two direction of magnetic field at that point which is contradiction.
Magnetic field lines are vector quantity. Outside the magnet they exit form north pole and enter south pole. Inside the magnet they are parallel to each other and travel south pole and north pole.
Magnetic field lines form closed loop.
In the region of strong magnetic field, lines are close to each other and in the region of weak magnetic field lines are far from each other. It means if you see rarer magnetic field lines indicate week field strength and denser magnetic field lines indicate strong magnetic fields.
Like poles repel and opposite poles attract.
How do we decide the north and south pole of magnet?
To find the answer of this question we can do small actvity.
Activity:
Take bar magnet and piece of thread.
Tie the string at the centre of magnet so that when magnet is hanged freely its horizontally balanced.
Hang the magnet freely, give it time to settle.
Observation:
You will notice that the magnet settles in north and south direction.
Now you can mark the oles of magnet. The pole which is in north direction is called north pole or north seeking pole and the pole which is in south is called south pole or south seeking pole
Types of magnets
Other than shapes, magnetics are classified based on their property of attraction or repulsion in magnetic field.
Some magnetic materials are strongly attracted some are weakly attracted towards a magnet and some are repelled form magnets
Ferromagnet
Diamagnet
Paramagnet
Ferromagnets:
The materials which are strongly attracted towards am magnet are called ferromagnet. Ferromagnet develops strong magnetism in presence of any other magnet. They suitable for making core electromagnets.
Examples of ferromagnet are Iron, nickel, cobalt and some alloys. Ferromagnets have high susceptibility in external magnetic field.
Diamagnets:
The materials which are repelled in presence of external magnetic field are called diamagnet. For example, Mercury, Copper, Inert gases etc.
Paramagnetic materials:
The materials which are weakly attracted towards a magnet in presence of external magnetic field are called paramagnetic. For example, Aluminium, Oxygen etc are paramagnetic material.
What are electromagnets?
An electromagnet is made of copper wire wounded on a iron core. Th copper wire is in the form of spring (helical wire). When current flows in the copper windings a strong magnetic field develops in winding and iron core. The electromagnet generates magnetic field lines like bar magnet when curent flows through it. It develops temporary north and south poles in presence of current.
Image below shows electromagnet and solenoid. You can guesss the diffrence between two. Electromagnets have iron inside and solenoids just copper coil.
