ELECTROMAGNETISM
Electromagnetism is the
effect produced by the interaction of an electric current with a magnetic field.
OR
Electromagnetism is the
production of a magnetic field by current in a conductor
MAGNETIC FIELD DUE TO A CURRENT –CARRYING CONDUCTOR
If a current of few
amperes is passes through a wire a weak magnetic field is produced.
NOTE:
The strength of the
magnetic field produced increases as the current passing through conductor
increases. (Strength of the magnetic field depends on the magnitude of the
electric current)
The effect of the magnetic
field can be detected by iron fillings when the current through the conductor reaches
20A.
The direction of the
magnetic field can be determined by applying two rules; Right-hand Grip Rule
and Maxwell’s cork screw rule
RIGHT-HAND GRIP RULE
The Right-Hand Grip Rule
states that;
“Imagine the wire
carrying the current is gripped by the right hand with the thumb pointing in
the direction of the convectional current, the fingers will curl around the
wire pointing in the direction of the magnetic field”
MAXWELL’S RIGHT-HAND CORK SCREW RULE
The Maxwell’s Right-Hand Cork
Screw Rule states that;
“If a
right-hand screw advances in the direction of the current, then the direction
of rotation of the screw represents the direction of the magnetic field due to
the current”
DIRECTION OF THE MAGNETIC FIELD DUE TO
CURRENT-CARRYING CONDUCTOR
FLEMING’S LEFT HAND RULE
The Fleming’s left hand
rule states that;
“If the first
three fingers of the left hand are held mutually at right angles to each other,
such that the middle finger points in the direction of the current, and the
forefinger in the direction of magnetic field lines, then the thumb points in
the direction of motion of the current-carrying conductor”
The Fleming’s left hand rule
determines the direction of the force acting on a current-carrying conductor in
a magnetic field. The Fleming’s left hand rule also known as Motor Rule
FORCE ON A CURRENT CARRYING CONDUCTOR IN A MAGNETIC
FIELD
When a current carrying
conductor is placed in a magnetic field, it experiences a force. This force
causes conductor to move when suspended freely.
NOTE:
The magnitude of the force
on the current-carrying conductor depends on;
Magnetic field strength:
Force on the current-carrying conductor is proportional to strength of the
magnetic field Fα B
Magnitude of current: Force
on the current-carrying conductor is proportional to the current through conductor.
Fα I
Conductor Length: Force on
the current-carrying conductor is proportional to the length of the conductor Fα L
Angle between magnetic
field and conductor: The magnitude of the force is proportional to the
component of the field that is at right angles to the conductor.
·
The force is at a maximum when the conductor is at right angles
to the field,
·
The force is zero when the conductor is parallel to the
field
FORCE DUE TO PARALLEL CONDUCTORS CARRYING CURRENT
When electric current
passes through parallel wires, a force is developed between them. The force
developed can be attractive or repulsive depending on the direction of the
current through the wires.
A.
When the current flow in
the same direction
Two
parallel wires that carry current in the same direction attract each other
When
the current flows in the same direction, the magnetic field between the
conductors (wires) cancel out while outside magnetic field add up. This causes
weak magnetic field between the conductors than on the outside, hence the
resultant force pushes the conductors towards each other.
B.
When the current flow in
the opposite direction
Two
parallel wires that carry current in the opposite direction repel each other
When
the current flows in the opposite direction, the magnetic field between the
conductors (wires) add up while outside magnetic field cancel out. This causes strong
magnetic field between the conductors than on the outside, hence the resultant
force is towards the outside of each conductor.
NOTE:
The Magnitude of the force
between parallel wires carrying current inversely proportional to the distance
between wires.
The shorter the distance of separation the stronger
the force of attraction or repulsion
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