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.
·
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;
i)
Magnetic field strength: Force on the current-carrying conductor is
proportional to strength of the magnetic field
∴
Fα B
ii)
Magnitude of current: Force on the current-carrying conductor is
proportional to the current through conductor. ∴ Fα I
iii)
Conductor Length: Force on the current-carrying conductor is
proportional to the length of the conductor
∴ Fα l
iv)
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
CLASS ACTIVITY
1.
Under what conditions does the charge affect a magnet?
2. The figure below shows
two parallel wires. What would be the effect of passing
a) Upward current through
both wires.
b) An upward current
through wire A and a download current through wire B?
