19 - Properties of
Magnetic field
Q 1. Fill in the blanks with the appropriate words:
(1)
The alloys called…………and……… are used for making industrial magnets.
(2) A
magnetic field can pass through …………. and ………………..
(3)
The intensity of a magnetic field is indicated by the lines of …………….
(4)
The real test of a magnet is .....................
Ans.
(1) Nipermag and alnico (2) cardboard and water (3) force (4) repulsion
Q. 2.
With whom should I pair up?
Ans.
(1)
Compass - A magnetic needle
(2)
Door of a cupboard - A magnet
3)
Repulsion - Like poles
(4)
Magnetic pole - The highest magnetic
force.
Q. 3.
Answer the following questions:
(1) Distinguish between the two methods of making an
artificial man
Ans.
Single-touch method Double-touch method
2. 'N pole of one bar magnet is rubbed over 2. Taking two bar magnets and placing
a
steel bar from the end A to the end B. their two opposite poles at the centre
of On repeating this procedure 15-20 again the
steel bar, both the magnets are rubbed and again magnetism is developed in the over the steel bar from one end to the
steel
bar. This method is called the other such as south pole of one
of magnet single-touch method. is at the 'A' end and the north pole
of the
another bar magnet is at the 'B' end. On
repeating
this procedure 15 to 20 times
again and again, magnetism is developed in
the
steel bar. This method is
called the double-touch method.
3. The
magnetism produced by this method 3. The
magnetism produced by this method
is of
low strength and lasts for a short
lasts longer as compared to that
of single
while. touch method.
(2) Which
substances are used for making electromagnets?
Ans.
Electromagnet is made using - an iron nail, copper wire of about 1 meter, a
battery and pins and can be tested.
(3)
Write a note on 'magnetic field'.
Ans. Michael Faradey proposed the idea of magnetic
lines of force to explain the magnetic field. The magnetism of a magnet acts
upon a certain distance from the magnet. The
space around the magnet in which the magnetic force acts on an object, is
called a magnetic field. The magnetic field around the magnet can be shown with
magnetic lines of force.
(4)
Why is a magnetic needle used in a compass?
Ans.
The magnetic needle used in a compass freely rotates and always settles in the north-south
direction as it is a property of a magnet. Thus, a magnetic needle can be used
to ascertain the direction.
Hence, magnetic needle is used in a compass.
(5) Explain with the help of a diagram how the
intensity and direction of the magnetic field of a bar magnet can be
determined.
Ans.
(1) The intensity of magnetic field is indicated by the magnetic lines of force
in that particular area. (2) Intensity of magnetic field in a particular area
can be understood by the number of field lines passing perpendicular through
that! unit area. The intensity of magnetic field is more where the lines of
force are more concentrated. (3) The direction of magnetic field is determined
by the directions of magnetic lines of force. The magnetic lines of force
always start from Magnetic field the north pole and end on the south pole. In
the similar manner, the direction of magnetic field is from north pole to south
pole.
(6) Give detailed information about how the merchants of olden times used a magnet while travelling.
Ans.
The merchants of olden times used to carry compass for ascertaining directions
while travelling. In a compass, a magnetic needle is fitted. This magnetic
needle supported on a sharp point can freely rotate in horizontal plane. If a
traveller goes anywhere while travelling, due to the property of a magnet,
magnetic needle always get settled in the north South direction. Once, the
north direction is known, other directions can be easily known. At the oceans
where only water is seen everywhere or at the desert areas where only sand is
seen everywhere, it becomes difficult to know the direction at night. At that
time, the compass to be helpful for merchants to know the directions.
