|
MAGNETIC EFFECT OF
ELECTRIC CURRENT
v Hans Christian Oersted discovered a relationship
between electricity and magnetism.
v A current carrying wire behaves as a magnet.[1]
v When a current passes through a wire, a magnetic
field is set up around the wire. This effect of current is called magnetic effect of current.
v Like magnetic poles repel each other and unlike
magnetic poles attract each other.
v Magnetic field is a space or region around a current
carrying wire or a magnet within which its influence is felt by a tiny
magnet.
v The path along which a free unit north pole moves in
a magnetic field is called magnetic field line.
The tangent at any point on a magnetic field line gives the direction of the
magnetic field at that point.
v No two magnetic field lines can intersect or cross
each other.
v Magnetic field lines are crowded in a region of
strong magnetic field.
v Magnetic field lines are far apart in a region of
weak magnetic field.
v When current passes through a straight wire or
conductor, a magnetic field is set up around the wire or the conductor.
v Magnetic field around a current carrying wire or
conductor is represented by concentric circles centered at the wire or the
conductor.
v The direction of magnetic field around the current
carrying conductor is determined by ‘Right Hand Thumb Rule’.
v Magnetic field around the current carrying wire
increases with the increase in the current passing through the wire.
v Magnetic field around the current carrying wire
decreases as we go away from the wire.
v Magnetic field due to a very long wire like a power
transmission line carrying current I and at a distance r from the wire is
given by, B = (µ0/4Π.).2.I/r, where, µ0
= 4Π X 10-7 Tm/A
v Two parallel conductors carrying current the same
direction attract each other.
v Two parallel conductors carrying current the
opposite direction repel each other.
v
The magnetic
field around a straight current carrying conductor can be increased by
bending it into a circular loop.
|
||||
|
v The strength of magnetic field produced at centre of
a circular loop of a wire is 1-directly proportional to the amount of current
passing through the loop of the wire, 2-directly proportional to the number
of turns of the circular loop of the wire, 3-inversely proportional to the
radius of the circular loop of the wire.
v Magnetic field produced by current carrying circular
wire or loop decreases on both sides along the axis of the circular wire.
v A solenoid is a
coil of many turns of an insulated copper wire closely wound in the shape of
a tight spring.
v Magnetic field inside a current carrying solenoid is
a uniform magnetic field.
v A solenoid carrying current behaves like a bar
magnet.
v A soft iron rod placed in a current carrying
solenoid is known as electromagnet.
v A current carrying conductor placed perpendicular to
the magnetic field experiences maximum force.
v The force acting on a current carrying conductor
placed perpendicular to the magnetic field B is given by, F = B.I.L
v Direction of force experienced by a current carrying
conductor placed in a magnetic field is determined by ‘Fleming’s Left Hand Rule’.
v No force acts on a current carrying conductor when
placed parallel to the magnetic field.
v SI unit of magnetic field is tesla(T).
v Force acting on a charge moving perpendicular to the
magnetic field is called ‘Lorentz Force’.
v Force acting on a charge Q moving with velocity v
perpendicular to the magnetic field is given by, F
= B.Q.v
v No force acts on a charge moving parallel to the
magnetic field.
v No force acts on a charge at rest in the magnetic
field.
v Direction of force experienced by a moving charge in
a magnetic field is determined by ‘Right Hand Rule’.
v Electric motor is a device which converts electrical energy into
mechanical energy.
v Electric motor works on the principle that a current
carrying conductor placed perpendicular to a magnetic field experiences a
force.
v The phenomenon of producing induced current in a
closed circuit due to the change in magnetic field in the nearby circuit is
known as ‘Electromagnetic Induction’.
|
||||
|
v More induced current flows through a closed coil if
a bar magnet is brought towards or away from the coil with large speed.
v No induced current flows through a closed coil if
magnetic field linked with it does not change.
v Direction of induced current in a conductor is
determined by ‘Fleming’s Right Rule’.
v Direct current is an electric current whose
magnitude is either constant or variable but the direction of flow in a
conductor remains the same.
v Frequency of direct current is zero.
v Alternating current is an electric current whose
magnitude changes with time and direction reverse periodically.
v In
v AC is more dangerous than DC.
v Electric generator is a device used to convert mechanical energy into
electrical energy.
v Electric generator works on the principle of electromagnetic
induction.
v To supply electric power from one place to another
place three wires known as phase wire(or live wire), neutral wire & earth
wire are used.
v The potential difference between the live wire &
neutral wire in a household supply of electric power is 220 V.
v Current rating of a fuse is the maximum amount of electric current
that can be passed through the fuse wire without melting it.
v Current rating of a fuse wire in a circuit having
bulbs & tubes is 5 A.
v Current rating of a fuse wire in a circuit having
heating appliance is 15 A.
v Electric fuse is a safety device used to save the
electrical appliances from burning when large current flows in the circuit.
v Electric fuse is made of a material of low melting
point.
v Material used for making a fuse wire is made of
copper.
v When live wire & neutral wire come in direct
contact, the resistance of the circuit becomes very small. Hence huge current
flows through the circuit. This huge current produces large amount of heat in
the circuit and the circuit catches fire. This is known as short circuiting.
|
||||
Er.
V. K. Pandey
