Another class 6 grade science ppt by me. This will tell you about chapter number 13 of NCERT science book. Please see.... thanks

1. Fun With
Magnets
Bhavya Mohindru

2. Magnets
 A magnet is a material or object that produces a magnetic field.
 This magnetic field is invisible.
 But it is responsible for the most notable property of a magnet: a
force that pulls on other ferromagnetic materials, such as iron, and
attracts or repels other magnets.

3. Discovery
 It is said that, there was a shepherd named Magnes, who lived in ancient
Greece.
 He used to take his herd of sheep and goats to the nearby mountains for
grazing. He would take a stick with him to control his herd. The stick had a
small piece of iron attached at one end.
 One day he was surprised to find that he had to pull hard to free his stick
from a rock on the mountainside. It seemed as if the stick was being
attracted by the rock. The rock was a natural magnet and it attracted the
iron tip of the shepherd's stick. It is said that this is how natural magnets was
discovered.

4. Magnetite/ Lodestone
 In Magnesia, rocks contained large numbers of black stones which
had the power to attract peices of iron.
 The Black Stone came to be known as Lodestone or The Leading
Stone because of the way it could be used to find directions.
 Today, it is known as the mineral magnetite ( Fe3 O4 ) and is found
in many countries.

5. Magnetic & Non - Magnetic
Substances
 Materials which get attracted
towards magnets are called
Magnetic Materials, for example,
Copper, Iron, Nickle.
 Magnets can attract or repel other
magnets and can attract any
magnetic material even if it is not
magnetised.
 Non - Magnetic materials, Such as
wood, paper, plastic & most
metals, don't get attracted towards
magnets.

6. Test For Magnetism : Compass
 We can use a compass to find out wether a substance is magnetic
or not.
 One end of the compass needle normally points to north. If a
magnetic substance comes close to needle, it will make the needle
turn.

7. Test For Magnetism : Repulsion
 Take a metal & a known magnet.
 Bring one pole ( N or S ) of a magnet near the ends of the metal bar
one by one.
 If both ends of the magnet get attracted towards the metal bar, the
bar is not a magnet.
 If one end attracts and the other repels the metal bar is a magnet.

8. Magnetic Compass
 The magnetic compass functions as a pointer to "magnetic north",
the local magnetic meridian, because the magnetized needle at its
heart aligns itself with the horizontal component of the Earth's
magnetic field.
 The magnetic field exerts a torque on the needle, pulling one end or
pole of the needle approximately toward the Earth's North magnetic
pole, and pulling the other toward the South magnetic pole.
 The needle is mounted on a low-friction pivot point, in better
compasses a jewel bearing, so it can turn easily.
 When the compass is held level, the needle turns until, after a few
seconds to allow oscillations to die out, it settles into its equilibrium
orientation.

9. Attraction & Replusion
 Two magnets will be attracted by
their opposite poles, and each will
repel the like pole of the other
magnet.

10. An Isolated Magnetic Pole Does'nt
Exist
 The Magnetic Poles always exist in pairs.
 When an attempt is made to separate the magnetic poles by
breaking a magnet , the it is observed that the two parts become a
complete magnet.
 New magnetic poles are developed at broken ends.
 Thus, an isolated magnetic pole does not exist i.e each magnet is
dipole.

11. Uses Of Magnets
 It is used in a Compass to find directions
 It is used in factories for lifting heavy masses of iron.
 It is used by surgeons in hospitals to remove steel splinters from the
wounds.
 It is used in construction of telephones, electric bells etc.
 It is used to separate iron & steel from non-magnetic materials.
 And Many many more.....