15 – Fun with Magnets
Q 1
Fill in the blanks.
Ans (1) If a bar magnet is hung by a thread tied at its
centre, its north pole becomes steady in the direction of the North Pole of the
earth.
(2) If a bar magnet is cut into equal pieces by cutting it
at right angles, 3 bar magnets are formed, and a total of 6 poles are formed.
(3) There is
repulsion between the like poles of a magnet, and attraction between its
opposite poles.
(4) When magnetic material is taken close to a magnet, the
material acquires induced magnetism.
(5) If a magnet attracts a piece of metal, that piece must
be made of magnetic metal or iron.
(6) A magnet remains steady in a north-south direction.
Q. 2. Which magnet will you use? Ans
(1) Iron is to be
separated from trash. Electromagnet
(2) You are lost in a
forest. Mariner’s compass
(3) A window shutter opens and shuts continuously in the
wind. Permanent magnet
Q. 3. How will you do this?
(1) Determine whether a material
is magnetic or non-magnetic.
Ans. The material should be taken
near to the magnet. If the material sticks to the magnet. the material is
magnetic. If it does not stick then it is non-magnetic.
(2) Explain that magnet has a certain magnetic field.
Ans. Keep a magnet in the centre of a paper. Spread iron
filings uniformly on the flat paper. The iron filings will get attracted to the
magnet only till a particular region. Beyond this region, the iron filings will
not get attracted. The region where iron filings are attracted
Is the magnetic field, whereas the region from where the
iron filings are not attracted will be the region with no magnetic field. This
experiment can give some idea about the extend of magnetic field of a magnet
(3) Find the north pole of a
magnet.
Ans. Suspend a magnet freely in the air with help of a
thread. The north pole of the magnet will point to the north direction while
the south pole of the magnet will point to the south direction. If the
directions are not known, then we can use mariner's compass. Take a magnet near
the mariner's compass. The pole which shows repulsion if taken near the north pole of a mariner's compass, will be
the north pole of this magnet.
Q. 4. Write the answers in your words:
(1) Write the
properties of magnet.
Ans. (1) A magnet always settles in the north-south
direction.
(2) At the two poles of a magnet, the magnetic force is
concentrated.
(3) If a magnet is divided into two parts. It forms two
independent magnets. Two poles of a magnet cannot be separated from each other.
(4) Between the like poles of a magnet, there is repulsion,
whereas between the opposite poles there is attraction.
(5) When a magnetic
material is placed near a powerful magnet, it acquires magnetism. This is known
as induced magnetism.
(6) Magnetic objects acquire
temporary magnetism if they are in the vicinity of a magnet.
(2) How is an electromagnet made ?
Ans. When an article of iron is wound by a copper wire and
the electric current is sent through the wire, the magnetism is produced in
this iron article. If the electric current is shut off, the magnetism is lost.
This is how temporarily magnetism can be produced by creating electromagnetism.
(3) What are the practical uses of a magnet?
Ans.(1) Pin holder, doorbell, doors of a fridge, car doors,
magnets attached to a fridge for decorations are some of the articles in which
magnets are used.
(2) The crane uses magnets which are very powerful. They are
usually electromagnets.
(3) The modern medical technique such as MRI (Magnetic
Resonance Imaging) also uses magnetism. ATM cards, credit cards and debit cards
also have a magnetic strip attached to them.
(4) Hard disc of computer, audio and video CD, etc. also use
magnetic materials.
