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THE PRAYAS TUTORIAL
MAGNETIC EFFECTS OF ELECTRIC
CURRENT
ASSIGNMENT(M
1. Magnetic field: It is the space around a magnet in which the force of attraction or
Repulsion due to the magnet can be detected. It has both magnitude and direction.
2. Magnetic field lines: It is the curved paths along which the iron filings arrange
Themselves due to the force acting on them in the magnetic field of the bar magnet.
3. Properties of Magnetic field lines: (i) It starts from the north pole of a magnet and
end at its south pole.
(ii) It is a closed and continuous curve.
(iii) They do not intersect one another.
(iv) They come closer to one another near the poles of a magnet but they are
widely separated at other places.
4. Oersted experiment: This experiment demonstrated that around every conductor
carrying an electric current, there is a magnetic field. The direction of deflection of the
needle due to magnetic field of a current carrying conductor is given by Ampere’s
Swimming Rule.
5. Magnitude of Magnetic field due to a current carrying straight conductor:
B  ( µo I ) / (2 π r)
Where B = Magnetic field
µo = Permeability of vacuum
I = Current flowing in conductor.
r = Distance from the conductor.
The magnetic lines of force round a straight conductor carrying current are concentric
circles whose centers lie on the wire.
The direction of magnetic field produced by is given by a straight conductor carrying
current Right –Hand Thumb Rule.
The SI unit of magnetic field is Tesla (T).
6. Magnetic field due to a current carrying circular coil
A circular coil consists of twenty or more turns of insulated copper wire closely wound
together. The magnetic field produced at the center of a circular wire of radius r and
carrying a current I is given by:
Magnetic field, B = (o I )/ (2r )
Where o = Permeability of free space (constant)
I = Current flowing through the wire
r = radius of the circular wire
7. Solenoid: It is a coil of many circular turns of insulated copper wire wrapped closely
in the shape of a cylinder.
The magnetic field produced by a current carrying solenoid is similar to the magnetic
field produced by a bar magnet. The strength of magnetic field produced by a current
carrying solenoid depends on: The number of turns in the solenoid
 The strength of current in the solenoid
 The nature of core material used in making solenoid
 The polarity of a solenoid can also be determined with the help of a Clock Rule.
The anti clockwise current in a face of the solenoid gives north polarity and
clockwise current gives south polarity.
8. Electromagnets and Permanent Magnets
(a). Electromagnets: It works on the magnetic effect of the current. It consists of a long
coil of insulated copper wire wound on a soft iron core. The core of the electromagnet
must be of soft iron because soft iron looses all of its magnetism when coil is switched
off.(b). Permanent Magnets: a permanent magnet is made from steel. As steel has
more retentivity than iron, it does not lose its magnetism easily.
Apart from steel alloys like Alnico (Aluminium, Nickel-Cobalt, alloy of iron) and
Nipermag (an alloy of Iron, Nickel, Aluminium and Titanium) are used to make very
strong permanent magnets.
9. Force on current carrying conductor placed in magnetic field
When a current carrying conductor is placed in a magnetic, a mechanical force is
exerted on the conductor which can make the conductor move.
The direction of the force is given Flemings left hand rule.
The magnitude of force acting on a current carrying conductor placed in a magnetic field
F = B × I ×L
Where
B= magnitude of magnetic field ,I = current flowing in the wire ,L= length of the currentcarrying wire placed in the magnetic field
10. Electric motor
A motor is a device which converts electrical energy into mechanical energy.
A motor works on the principle that whenever a current carrying conductor is placed in a
magnetic field, it experiences a force given by Fleming’s left hand rule.
11. Electromagnetic induction: It is the phenomenon of producing induced current in
a moving conductor or coil in a magnetic field. It was discovered by Faraday. The
direction of the induced current is given by Fleming’s right hand rule.
The potential difference corresponding to induced current is induced potential
difference (pd) or induced electromotive force (emf).
12. Electric generator: It converts mechanical energy into electrical energy. It works on
principle of electromagnetic induction.
13. Direct current and alternating current: The current which does not change in
direction and magnitude is called direct current (D.C).
The frequency of the D.C current is zero.
The current which changes its magnitude and direction after a certain fixed interval of
time is called alternating current.
The frequency of the alternating current in India is 50 HZ.
14. Domestic electric circuits: Usually there are two separate circuits in a house, the
lighting circuit with a 5A fuse and the power circuit with a 15A fuse.
All electrical appliances like bulbs, fans and sockets, etc., are connected tin parallel
across the live wire and neutral wire.
If a straight conductor is held in right hand, such that thumb point along the direction of
the current, then the tips of the finger show the direction of magnetic field or magnetic
lines of force. This is known as the Right -Hand Thumb Rule
According to Fleming’s left-hand rule: Hold the forefinger, the centre finger and the
thumb of your left hand at right angles to one another. Adjust your hand in such a way
that the forefinger points in the direction of the magnetic field and the centre finger
points in the direction of current, the direction in which thumb points, gives the direction
of force acting on the conductor.
ALTERNATING CURRENT (AC) GENERATOR:
It converts mechanical energy into electrical energy.
Principle:
It works on the principle of electro magnetic induction i.e When a coil is rotated in
uniform magnetic field , electric current is induced in the Coil.
Construction:
Main components of a.c generator are given below :
1. Armature (abcd ): It consists of a large number of turns of insulated copper wire
wound over a soft iron core.
2. Field Magnet: It produces magnetic field. The armature coil rotates between the
pole pieces of the field magnet.
3. Slip Rings: The two ends of the armature coil are connected to two hollow metal
rings. These rings rotate along with armature coil.
4. Brushes or Sliding Contacts: B1 and B2 are flexible metal plates or carbon rods.
These are called brushes. The brushes remain fixed while slip rings rotate along
with the armature.
 Diagram –Refer NCERT TEXT BOOKWorking:
As the armature coil is rotated about an axis , the magnetic flux linked with
armature changes. Therefore, an induced current is produced in the armature coil.
(a) Let us suppose that the armature coil ABCD is rotating anti-clockwise so that the
arm BA moves inwards and CD moves outwards. Applying Fleming’s Right Hand
Rule, we find that the induced current in the armature coil and in the circuit is due
to which galvanometer (G) shows deflection towards right.
(b) After the armature coil has turned through 180°, it occupies the position as
shown in the fig.. With the armature coil rotating in the same direction, CD
moves inwards and BA moves outwards. Thus, again applying Fleming’s Right
Hand rule, we find the induced current in the external circuit flows in the opposite
direction due to which the direction of deflection in galvanometer is towards left.
Direct current: The current which has a constant magnitude and same direction is
called direct current (D.C). The frequency of the D.C current is zero.
Alternating current :The current which changes in magnitude and direction at regular
interval of time is called alternating current.Frequency of AC is the number of cycles
per second made by the current. The frequency of the alternating current in India is 50
HZ.
Advantages of AC over DC :
1. A.C can be transmitted over long distances without much loss of energy.
2. A.C can be produced easily and cheaply than D.C.
3.A. C voltage can be transformed to any desired value with help of a transformer.
4. A.C can be converted into D.C when required.
Disadvantages of A.C over D.C:
1. A.C is more dangerous than DC
2. A.C cannot be used for electroplating, electrotyping and other electrolytic
processes.
Best wishes
sinha
Rajiv