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Magnetism And Matter

Question
CBSEENPH12037725
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A short bar magnet placed in a horizontal plane has its axis aligned along the magnetic north-south direction. Null points are found on the axis of the magnet at 14 cm from the centre of the magnet. The earth's magnetic field at the place is 0.36 G and the angle of dip is zero. What is the total magnetic field on the normal bisector of the magnet at the same distance as the null point (i.e., 14 cm) from the centre of the magnet? (At null points, field due to a magnet is equal and opposite to the horizontal component of earth’s magnetic field).

Solution
Bar magnet is placed such that its axis is aligned along the magnetic N-S direction. As the null points are found on the axis of the magnet, it shows that south pole of the magnet faces the Geographical North direction. (as shown in fig.). 

 

In this case, magnetic moment M→ is antiparallel to the earth's field.
Since angle of dip is zero, the horizontal component of the earth's magnetic field equals the field itself.
In this case i.e., magnetic field at the axis is,

μ0 2M4πr3 = 0.36 G       Bax  = -.36 G 

From the figure, total magnetic field at the normal bisector of the magnet at the same distance as the null point (r = 14 cm) from the centre of magnet is given by,

 = Beq+BH 

= μ0M4πr3+0.36= 0.362+0.36 = 0.54 

That is, the total magnetic field is 0.54 G in the direction of earth's field.

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Some More Questions From Magnetism and Matter Chapter

Answer the following question regarding earth:
Geologists claim that besides the main magnetic N-S poles, there are several local poles on the earth's surface oriented in different directions. How is such a thing possible at all?

Answer the following question:
The earth's magnetic field varies from point to point in space. Does it also change with time? If so, on what time scale does it change appreciably?

Answer the following question:
The earth's core is known to contain iron. Yet geologists do not regard this as a source of the earth's magnetism. Why?

Answer the following question:
The charged currents in the outer conducting regions of the earth's core are thought to be responsible for earth's magnetism. What might be the ‘battery’ (i.e., the source of energy) to sustain these currents?

Answer the following question:
The earth may have even reversed the direction of its field several times during its history of 4 to 5 billion years. How can geologists know about the earth's field in such distant past?

Answer the following question:
The earth’s field departs from its dipole shape substantially at large distances (greater than about 30,000 km). What agencies may be responsible for this distortion?

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