21. How will you identify whether the magnetic field at a point
is due to earth or due to some current carrying conductor?
I will identify
whether
the magnetic field at a point is due to earth or due to some
current carrying conductor by knowing the nature of magnetic
field whether it is uniform or non-uniform. If the magnetic
field is uniform then the magnetic field at a point is due
to the earth but of the magnetic field is non-uniform then
the magnetic field is due to some current carrying
conductor.
22. When three
identical bar magnets are placed in the form of equilateral
triangle with the North Pole of one touching the South Pole of
the other. What will be the magnetic moment of the system?
When three
identical bar magnets are placed in the form of equilateral
triangle with the North Pole of one touching the South Pole
of the other. The net magnetic moment of the system
becomes zero because no pole is free at either side of each
pole as there is a force of attraction between each joining.
23. Is it possible to construct a magnet with three poles?
Justify your answer.
Basically,
magnetic poles always occur in pair but it is possible to
construct a magnet with three poles if two bar magnets are
arranged to produced a magnetic field configuration of three
poles. It can be done by keeping North poles or South poles
of two magnets together.
24. Does magnetic
monopole exist? Explain.
The poles of a
magnet exits in pair and have equal strength. The
magnet never exits having monopole i.e. an isolated magnetic
pole doesn't exits.
For example
when a magnet is broken down into pieces, each small piece
behaves as a magnet having two poles. Hence, magnetic
monopole does not exits.
25. A piece of iron is in touch with a powerful magnet. The iron
too develops magnetic property. Explain how.
A piece of iron
is in touch with a powerful magnet. The iron too develops
magnetic property. The magnetic substances i.e. iron contains
a large number of magnetic domains which are oriented
randomly in all directions so there is no magnetic effect.
When the powerful magnet touches iron then the magnetic
field of the magnet causes alignment of magnetic domains of
iron in one direction along the magnetic field so that the
iron becomes temporary magnet. Hence, the iron too develops
magnetic property when it is in touch with a powerful
magnet.
26. When a magnet is broken down
into pieces, each small piece behaves as a magnet. Why?
According to
domain theory, a magnet contains numerous tiny molecular
magnets associated with a domain have their magnetic axes
oriented in same direction. So, each domain behaves like a
tiny magnet having two poles. When a magnet is broken down
into pieces, each broken piece contains domain or group of
domain oriented in same direction. As the domain behaves
like magnet so, when a magnet is broken into pieces, each
piece behaves as a magnet.
27. What may happen if a bar magnet
is dropped on a floor or hammered?
A bar magnet
loses its magnetism via shock such as being dropped or hit
with a hammer. This really only applies to older materials
such as magnetic steels and Alnico materials; the mechanism
that creates coercivity means that they are susceptible to
being demagnetized if enough energy is transmitted through
the material via a shock, such as being dropped or hit with
a hammer. Modern materials do not suffer this type of
problem.
Hence,
if a bar magnet is dropped on a floor or hammered then a bar
magnet loses its magnetism.
28. Why is the amplitude of
oscillation magnetometer small?
The oscillation
magnetometer works on the principle of simple harmonic
motion principle. When the amplitude of oscillation
magnetometer is taken small then the sine of the angular
displacement of the magnet from its mean position is equal
to its angular displacement but if we take large amplitude
of oscillation magnetometer then sine of the angular
displacement of the magnet from its mean position cannot be
equalize to its angular displacement. For accuracy in
the measurement of time period using simple harmonic motion
principle, the amplitude of oscillation magnetometer is
small. Hence, the amplitude of oscillation magnetometer is
small.
29. Will the time
period of a vibration magnetometer change if the magnets are of
larger dimension? Why?
Yes,
if the magnets are of larger dimension then the time period
of a vibration magnetometer surely changes i.e. it
increases. The time period for the vibration magnetometer is
given as
The time period
varies directly to the square root of moment of inertia. The
momentum of inertia increases in the dimensions so, there is
change in time period of a vibration magnetometer if the
magnets are of larger dimensions.
30. How can you
determine which one is stronger if you are given two magnets of
the same size and mass using the vibration magnetometer?
The time period
for the vibration magnetometer is given as
From above
relation, the time period of vibration magnetometer varies
inversely to the square root of magnetic moment. Stronger
the magnet, larger will be its magnetic moment and
vice-versa. From above relation, stronger the magnet less
will be its time period. By determining the time period from
vibration magnetometer, we are able to determine the
stronger magnet from given two magnets.
31. Can you plot
the lines of the earth’s magnetic field? What are their shapes?
Yes, we can
plot the lines of the earth's magnetic field. It is believed
that the earth behaves as a huge magnet with its magnetic
north pole towards the geographical south & the south pole
towards the geographical north pole. The earth contains
the magnetic lines of force whose direction is from the
geographical south to the geographical north. The magnetic
poles of the earth's magnet are very far apart from each
other so, the magnetic lines of force over any small portion
of the earth's surface are parallel to each other i.e. of
magnetic lines of force are plotted on a paper, parallel
lines are obtained.
32. Do the magnetic
elements remain the same at every place with time?
As the magnetic
elements varies with the time so, the magnetic elements do
not remain the same at every place with time because there
are some periodic variation that are secular change, daily
variations, actual changes and irregular changes.
33. What are the
factors, which are responsible to make a permanent magnet?
Substances that
are used for making permanent magnets should have high
retentivity and high coercivity. For example: steel & alnico
are used to make permanent magnet. High retentivity and high
coercivity are the factors that a substance must possess to
make a permanent magnet.
34. What type of substance will you prefer for the core of
transformer? Why?
Substances
having high retentivity, low coercivity and low hysterisis
loss are used to make the core of transformer as these
materials can easily lose the magnetism when the current is
switched off. For example: soft iron, radio-metal, etc are
used for the core of transformer.
35. Why is it
easier to demagnetize soft iron than the steel?
It is easier to
demagnetize soft iron than the steel because the coercivity
of soft iron is less than that of the steel. As a result,
the area of the hysteresis loop for soft iron is smaller
than that for the steel. Thus, the loss of energy per cycle
is less for iron than for steel and if loss of energy is
less it results easier to demagnetize. So, it is easier to
demagnetize soft iron than the steel.
36. When a magnetic
needle is located right on geo-magnetic north or South Pole,
which direction does it point?
The horizontal
components of the earth's magnetic field vanish at the North
or South poles. hence only vertical magnetic field of the
earth will be there. Due to this, a magnetic needle is free
to move in a horizontal planes. So, a magnetic needle will
point any direction on the geo-magnetic North or South pole.
37. Can the earth’s
magnetic field be vertical at a place? What will happen to a
freely suspended at such a place? What is the value of dip
there?
Yes, the
earth's magnetic field can be vertical at a place i.e. at
poles. At poles, the value of angle of dip is 900.
Using tangent law, the magnet placed at poles will make
angle of 900
i. e. the magnet will be vertical at such place.
38. The angle of dip in Britain is
greater than that in Kathmandu. Why?
The angle of
dip at a place is defined as the angle made between the
direction of the resultant intensity of the earth's magnetic
field and the horizontal line at that place. As the latitude
increases, the value of angle of dip also increases. The
latitude in Britain is higher than that in Kathmandu. So,
the angle of dip in Britain is greater than that in
Kathmandu.
39. Why does a bar magnet not retain
its magnetism when it is melted?
If a bar magnet
is heated,
due to the heat energy, the tiny
molecular magnet regains the kinetic energy and orient
themselves in any directions. And when it melts, the orientation of the
molecular magnets are completely changed and they are
arranged in random or haphazard fashion and cannot arrange
the position of molecular magnets in same direction as
initially. Hence, a bar magnet does not retain its magnetism
when it is melted.
40. A bar magnet made up of iron is heated
to 10000C
and then cooled in a magnetic field free space. Will it retain
magnetism?
If a bar magnet
made up of iron is heated to 10000C which is
quite above the curie's temperature i.e. 7500C.
Due to the fall in susceptibility above curie temperature all its atomic
magnets are randomly oriented so, these materials becomes
paramagnetic materials above curie's temperature. Thermal
motion gained due to thermal energy at this temperature
destroys its magnetism. Again, if it is cooled, it will not
retain or gain its magnetism.
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