Magnetic Field Lines
Activity 2
Place a magnet over a
cardboard. Sprinkle some iron-filings on the cardboard. Tap the card board
gently. We observe that the iron filings align themselves in definite pattern.
These patterns are called magnetic lines of force.
Activity 2 shows that
magnets have some curved lines around them and these lines are called magnetic
field lines. is can also be inferred by placing a test magnet in the magnetic
field of another magnet. rough the direction the test magnet moves, magnetic
field lines can be identified. The magnetic field lines start at north pole and
ends at south pole as shown in the Figure 3.4(a)
A magnetic field line is
de ned as a curve drawn in the magnetic field in such a way that the tangent to
the curve at any point gives the direction of the magnetic field as shown in
the Figure 3.4 (b). In the Figure 3.4 (b), the arrow mark indicates the
direction of magnetic field at points A, B and C. Note carefully that the
magnetic field at a point is tangential to the magnetic Field lines.
We all know that earth
also behaves like a magnet and the magnetic field lines of earth’s is shown in
the figure 3.5
Magnetic flux is the
number of magnetic field lines passing through a given area as shown in the
figure 3.6. It is denoted by Ï• and its unit is weber (Wb).
The number of magnetic
field lines crossing unit area kept normal to the direction of field lines is
called magnetic flux density. It is shown in the figure 3.7. Its unit is Wb/m2
·
Magnetic lines of force are closed continuous curves, extending
through the body of the magnet.
·
Magnetic lines of force start from the North Pole and end at the
South Pole.
·
Magnetic lines of force never intersect.
·
They will be maximum at the poles than at the equator.
·
The tangent drawn at any point on the curved line gives the
direction of magnetic field.
What does happen when
two magnets are placed near each other? ere are four ways we can keep them. ey
are shown in Fig 3.8
(a) two unlike poles
facing each other, (b) two like poles facing each other, (c) parallel magnets
with same poles facing same side and (d) parallel magnets with opposite poles
facing same side. All these positions are.
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