History of Magnets:
According to
Greek legend, magnetism was first discovered by a shepherd named Magnes,
who lived in Magnesia, Greece. Magnes was herding his sheep through the
mountains. Suddenly he noticed the ferrule of his stick and nails in his
sandals got stuck to a rock. The iron in his stick and nails had become
attracted to the magnetic rock. The stone was named magnetite. Magnetite was
first discovered at a place called Magnesia. The substances having the property
of attracting iron are now known as magnets.
MAGNETIC AND NON-MAGNETIC
MATERIALS:
We understand that magnet attracts certain materials whereas some do not get attracted towards magnet. The materials which get attracted towards a magnet are magnetic – for example, iron, nickel or cobalt. The materials which are not attracted towards a magnet are non-magnetic.
POLES OF MAGNET:
The two poles
of the magnet are the north and south poles. The poles of a magnet are its
ends. The pole at the beginning or end is called the North Pole and the other
is called the South Pole.
A freely
suspended magnet always comes to rest in north-south direction.
The directive property of magnets has been used for centuries to find
directions. Around 800 years ago, the Chinese (an
emperor in China named Hoang Ti.) discovered that a suspended lode stone stops in the north-south
direction. Chinese used these lode stones to find directions.
MAKE YOUR OWN MAGNET:
There are
several methods of making magnets. Let us learn the simplest one. Take a
rectangular piece of iron. Place it on the table. Now take a bar magnet and
place one of its poles near one edge of the bar of iron. Without lifting the
bar magnet, move it along the length of the iron bar till you reach the other
end.
Now, lift the magnet and bring the pole. Move the magnet again along the iron bar in the same direction as you did before. Repeat this process about 30-40 times. Bring a pin or some iron filings near the iron bar to check whether it has become a magnet.
ATTRACTION AND REPULSION
BETWEEN MAGNETS:
When two
opposite magnetic poles are close, they attract each other. When like poles are
pushed together, there is a force of repulsion. The rule for magnets is
that like poles repel and unlike poles attract.
KEYWORDS:
Compass, Magnet, Magnetite, North Pole,
South Pole, Attraction, Repulsion
Exercise Questions:
1.
Fill in the blanks in the following
(i)
Artificial magnets are made in different shapes such as __________, __________
and ____________.
(ii)
The materials which are attracted towards a magnet are called________.
(iii)
Paper is not a ______ material.
(iv)
In the olden days, sailors used to find direction by suspending a piece of
___________.
(v) A
magnet always has __________ poles.
Answer:
(i)
Artificial magnets are made in different shapes such as bar magnet, horse
shoe and cylindrical.
(ii)
The materials which are attracted towards a magnet are called magnetic.
(iii)
Paper is not a magnetic material.
(iv)
In the olden days, sailors used to find direction by suspending a piece
of magnet.
(v) A
magnet always has two poles.
2. State
whether the following statements are true or false:
(i) A
cylindrical magnet has only one pole.
(ii)
Artificial magnets were discovered in Greece.
(iii)
Similar poles of a magnet repel each other.
(iv)
Maximum iron filings stick in the middle of a bar magnet when it is brought
near them.
(v)
Bar magnets always point towards North-South direction.
(vi) A
compass can be used to find East-West direction at any place.
(vii)
Rubber is a magnetic material.
Answer:
i)
False
ii)
False
iii)
True
iv)
False
v) True
(Freely suspended bad magnet)
vi)
True
vii)
False
3. It
was observed that a pencil sharpener gets attracted by both the poles of a
magnet although its body is made of plastic. Name a material that might have
been used to make some part of it.
Answer:
Iron might
have been used to make some part of it.
4.
Column I shows different positions in which one pole of a magnet is placed near
that of the other. Column II indicates the resulting action between them for
each situation. Fill in the blanks.
|
Column – I |
Column – II |
|
N-N |
_______ |
|
N-___ |
Attraction |
|
S-N |
_____ |
|
___-S |
Repulsion |
Answer:
|
Column – I |
Column – II |
|
N-N |
Repulsion |
|
N- S |
Attraction |
|
S-N |
Attraction |
|
S– S |
Repulsion |
5.
Write any two properties of a magnet.
Answer:
Properties
of a magnet are as follows
It
attracts objects made of Nickel, Cobalt and Iron.
Like
poles of two magnets repel each other and opposite poles attract each other.
6.
Where are poles of a bar magnet located?
Answer:
On two
ends of a bar magnet.
7. A
bar magnet has no markings to indicate its poles. How would you find out near
which end is its north pole is located?
Answer:
A bar
magnet is hung in the air, and the end pointing to the north is the north pole
of the magnet.
8. You
are given an iron strip. How will you make it into a magnet?
Answer:
Take a
bar magnet and keep in contact with one of its poles with one edge of the bar
of iron.
Without
lifting the bar magnet, move it along the length of the iron bar till you reach
the other end.
Lift
the magnet and bring the pole (the same pole you started with) to the same
point of the iron bar from which we began.
Move
the magnet again along the iron bar in the same direction as you did before.
Repeat
this process for about 30-40 times.
9. How
is a compass used to find directions?
Answer:
A
compass always shows north and south directions; by keeping this as a
reference, we can always find east and west directions also.
10. A
magnet was brought from different directions towards a toy boat that has been
floating in water in a tub. The effect observed in each case is stated in
Column I. Possible reasons for the observed effects are mentioned in Column II.
Match the statements given in Column I with those in Column II.
|
Column I |
Column II |
|
Boat
gets attracted towards the magnet |
Boat
is fitted with a magnet with a north pole towards its head |
|
Boat
is not affected by the magnet |
Boat
is fitted with a magnet with a south pole towards its head |
|
Boat
moved towards the magnet when the north pole was brought near its head |
Boat
has a small magnet fixed along its length |
|
Boat
moves away from the magnet when the north pole is brought near its head |
Boat
is made up of magnetic material |
|
Boat
floats without changing its direction |
Boat
is made up of non-magnetic material |
Answer:
|
Column I |
Column II |
|
Boat
gets attracted towards the magnet |
Boat
is made up of magnetic material |
|
Boat
is not affected by the magnet |
Boat
is made up of non-magnetic material |
|
Boat
moved towards the magnet when the north pole was brought near its head |
Boat
is fitted with a magnet with the south pole towards its head |
|
Boat
moves away from the magnet when the north pole is brought near its head |
Boat
is fitted with a magnet with a north pole towards its head |
|
Boat
floats without changing its direction |
Boat
has a small magnet fixed along its length |
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