2. z
ACTIVITY
Take a straight thick copper wire and
place it between the points X and Y in
an electric circuit, as shown in Fig. The
wire XY is kept perpendicular to the
plane of paper.
Horizontally place a small compass
near to this copper wire. See the
position of its needle.
Pass the current through the circuit by
inserting the key into the plug.
Observe the change in the position of
the compass needle.
3. z
Hans Christian Oersted (1777–1851)
Hans Christian Oersted, one of the leading
scientists of the 19th century, played a crucial
role in understanding electromagnetism.
In 1820 he accidentally discovered that a
compass needle got deflected when an electric
current passed through a metallic wire placed
nearby.
Through this observation Oersted showed that
electricity and magnetism were related
phenomena.
His research later created technologies such as
the radio, television and fiber optics.
The unit of magnetic field strength is named the
oersted in his honor.
6. zMAGNETIC FIELD AND FIELD LINES
The portion of space near a magnetic body or a current-
carrying body in which the magnetic forces due to the body
or current can be detected is called magnetic field.
Magnetic lines of force are the lines that depict
the magnetic force that exists in the surrounding
of the magnet.
7. zThe properties of
magnetic lines of
force are as
follows.
Each line is a closed and continuous curve.
Outside a magnet, magnetic field lines are
directed from North pole to South pole.
The direction of field lines inside the magnet
is from the South pole to the North pole.
8. z
They will never intersect each other.
They are crowded near the poles
where the magnetic field is strong.
The direction of field line is along
the tangent made at that point in the
field line towards the field.
The strength of the magnetic lines is
the same throughout and is
proportional to how close are the
lines.
The properties of magnetic lines of force are as
follows.
10. z
Fig. 13.3 - Magnetic lines of
force are the lines that depict
the magnetic force that exists
in the surrounding of the
magnet
11. z
Q) Why does a compass needle get deflected when
brought near a bar magnet?
Ans. A compass needle is a small bar magnet. When it is
brought near a bar magnet, its magnetic field lines interact
with that of the bar magnet. Hence, a compass needle shows
a deflection when brought near a bar magnet.
Concept Insight: Magnetic fields interact with each
other. Interaction of magnetic field of earth and that of the
compass needle is used to find directions.
12. zQ) Why don’t two magnetic field lines intersect
each other?
Ans. No two field-lines are found to
cross each other. If they did, it would
mean that at the point of intersection,
the compass needle would point
towards two directions, which is not
possible.
13. zRight Hand Thumb Rule
Imagine that you are holding a
current-carrying straight conductor
in your right hand such that the
thumb points towards the direction
of current. Then your fingers will
wrap around the conductor in the
direction of the field lines of the
magnetic field, as shown in Fig.
This is known as the right-hand
thumb rule*.
B : Magnetic field Intensity
I : Value of current
