Transcript Magnetic Effects of Electric Currents

Magnetic Effects of
Electric Currents
The magnetic effect of an
electric current.
When an electric current passes through a wire, a
magnetic field is produced around the wire. If the wire
is wound into a coil the resulting field is similar to that
of a bar magnet wit north and south poles.
Predicting the direction of the field
around a current carrying conductor.
Maxwell’s screw rule:
Imagine that a right handed screw is
turned so that it moves forward in
the direction of convectional current.
Then, its direction of rotation
indicates the direction of the
magnetic field due to the current.
Predicting the direction of the field
around a current carrying conductor.
You can also use the right hand grip rule, which
says:
If a conductor carrying a current is gripped with
the right hand, with the thumb pointing along
the conductor in the direction of conventional
current, the curl of the fingers around the
conductor indicates the direction of the
magnetic lines of force.
Electromagnets
An electromagnet is a temporary magnet
which has magnetism only when
current is passing through a coil wire.
The strength of the magnetic field
associated with an electromagnet can be
increased by
• Increasing the current
• Increasing the number of turns pf coil
per length
• Including a soft iron core.
Applications of
electromagnets
• To lift iron rods and steel bars.
• As cranes in scrap yards
• In hospitals to remove splinters
from eyes.
• In electric bells
• In the cores of transmissions
• In control systems.
The magnetic Relay
The basic relay consists of a coil and
a set of contacts. When voltage is
applied to the coil, current passes
through the wire and creates a
magnetic filed. The magnetic field
pulls the contacts together and
hold them there until the current
flow is stopped.
Magnetic Relay
The force on a current carrying
conductor in a magnetic field.
The direction of the force which results
from the interaction of a current and a
magnetic field can be predicted by’
Fleming's Left Hand Rule’.
Fleming's Left Hand Rule.
• The first finger is the direction of
the field
• The second finger is the direction of
current.
• Thumb is the movement of the
wire.
A current carrying
conductor in a magnetic
field.
• Above the conductor, the field of the
conductor and that of the magnet are
acting in the same direction. The
field is strengthened.
• Below the conductor, the field of the
conductor and that of the magnet ar
in the opposition. The field is
weakened.
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