Magnetic effects of current

1. MAGNETIC EFFECTS OF
ELECTRIC CURRENT

2. Topics covered :
1.Introduction: Magnetic properties
2.Magnetic Effect of Current – Oersted’s Experiment
3. Maxwell’s Cork Screw Rule
4.Right Hand Thumb Rule
5.Magnetic Field due to Infinitely Long Straight Current –
carrying Conductor
6.Magnetic Field due to a Circular Loop carrying current
Topics to be covered :

3. 7. Magnetic Field due to a Solenoid
8. Fleming’s left hand rule
9. Electric motor(AC/DC)
10. Electromagnetic Induction and Fleming’s right hand rule
11. Electric generator (AC/ DC): Dynamo
12. Domestic electric circuit
Topics covered :

4. Introduction: Magnetic properties
1. They have two permanent poles namely, North and South and
poles cannot be isolated.
2. Like poles repel each other and unlike poles attract each other.
3. When magnet is cut into pieces they will behave like separate
magnets with same property but lesser magnetic strength
compared to whole magnet.
4. The freely suspended bar magnet will align in geographic
N – S direction.

5. 1. When magnet is subjected to mechanical damages (falling on a hard
surface, heating, piling, hammering etc.) they lose their magnetic
properties.
2. Magnets attract iron like substances, Fe, Co, Ni etc.
3. Depending on application we have, i) dumbbell magnet, ii) ring
magnet, iii) bar magnet, iv) horse shoe magnet, v) compass needle,
vi) round magnet, vii) circular magnet etc.
Note: 1. There is a magnet without poles is called toroid, whose north and
south poles are joined.
2. Magnets are naturally available (Earth) and can be prepared
artificially for use.
Properties of Magnets

6. MAGNETIC FIELD AND FIELD
LINES
MAGNETIC FIELD
Definition: Magnetic field is space or region surrounding the
magnet (or current carrying conductor) in which another
magnet will experience the force of magnetostatics.
It is denoted by ‘B’ SI unit T (tesla) and is a vector.
MAGNETIC FIELD LINES
Definition: Magnetic field lines are the imaginary path in which
an isolated north pole can travel from one pole to another in
space.

7. 1.Magnetic field lines or Magnetic lines of force, travel from north pole
and reach south pole in its vicinity or travel up to infinity.
1.Magnetic Field Lines are continuous closed curves and can pass through
conductors
2.Note: Superconductors does not allow Magnetic Field Lines to enter inside
hence magnetic field, B = 0 (inside).
3.The tangent drawn at any point on the Magnetic Field Lines gives direction
of Magnetic Field at that point.
4.No two Magnetic Field Lines can intersect each other since two value of
Magnetic Field doesn’t exist at a point.
5.Magnetic Field Lines are crowded at poles (strong Magnetic Field) but
diverged at weak Magnetic Field region.

8. MAGNETIC FIELD LINES OF A BAR MAGNET
Experimental image Illustrative diagram

9. Magnetic Effect of electric Current
An electric current (i.e. flow of electric charge) produces magnetic effect
in the space around the conductor called Magnetic field.
Hans Christian Oersted’s Experiment:
When current is passing through the wire over the
compass needle in anti-clockwise direction, the needle
was found to deflect towards West direction from its
normal position.
When current direction is reversed through the wire
over the compass needle, the direction of needle also
reversed.

10. Maxwell’s Cork Screw Rule
or Right Hand Screw Rule:
If the forward motion of an imaginary right
handed screw is in the direction of the current
through a linear conductor, then the direction of
rotation of the screw gives the direction of the
magnetic lines of force around the conductor. B
B
I I

11. Right Hand Thumb Rule or Curl Rule
If a current carrying conductor is imagined to be held in the
right hand such that the thumb points in the direction of the
current, then the tips of the fingers encircling the conductor will
give the direction of the magnetic lines of force.
I
B

12. Magnetic Field Lines due to current
carrying conductor
Direction of B is determined by Right Hand Screw Rule.
It is perpendicular to the plane of the diagram and entering into the plane
at as shown in diagram.
B
I
I
B

13. I I
Different views of direction of current and magnetic
field due to circular loop of a current carrying coil:
B
I
I
B B
Current moving in clockwise
direction representing the
face towards us (Outwards)
as South pole of bar magnet
Current moving in anticlockwise
direction representing the face
towards right (outwards) as North
pole of bar magnet

14. Magnetic Field due to a current carrying
Solenoid:
TIP: When we look at any end of the coil carrying current, if the
current is in anti-clockwise direction then that end of coil behaves
like North Pole and if the current is in clockwise direction then that
end of the coil behaves like South Pole. Hence it behave like bar
magnet.
I I
x
x
x
x
x x
x
B

15. Force acting on a current carrying
conductor:
When a current
carrying conductor placed between
two poles of horseshoe magnet
experience force (motion)
depending on direction of current
and magnetic field applied inwards
or outwards.

16. FLEMING’S LEFT HAND RULE:
I
Stretch first three fingers of your left
hand mutually perpendicular to each
other such that, fore (Index) finger
represents direction of magnetic field,
middle finger represent direction of
current, then thumb finger show the
direction of force (motion) of the
conductor.

17. ELECTRIC MOTOR:
AC MOTOR:
DC MOTOR:

18. The device which converts electrical energy (AC/DC current)
into mechanical energy.
Principle: When a current carrying conductor placed between
magnetic field it will undergo rotation based on Fleming’s left hand
rule.
Working: Current passing through armature will experience opposite
force at two ends of poles and start rotating, the commutators help in
changing direction according to AC/DC cycle with external source.
Application: Fan, mixer, blen
der, washing machine etc.
AC/DC MOTOR:

19. The relative motion between closed conducting wire and magnet
will induce electric current in the coil without any electrochemical
reaction.
Faraday’s Experiments:
Faraday’s Electromagnetic Induction:
Current
direction

20. Stretch first three fingers of
your right hand mutually perpendicular
to each other such that, fore (Index)
finger represents direction of magnetic
field, middle finger represent direction of
current induced, then thumb finger show
the direction of force (motion) of the
conductor.
Fleming’s right hand rule:

21. ELECTRIC GENERATOR:
It is a device which converts mechanical energy into electrical
energy (AC/DC).
AC : Alternating current and DC : Direct current
Principle: When a coil is rotated between magnetic field there will be
induced current/emf based on Electromagnetic Induction.
Load
Resistor

22. ADVANTAGES OF AC OVER
DC
1. The cost of producing AC much lesser than that of DC.
2. AC can be easily converted into DC using rectifier.
3. AC can be easily transmitted for long distances compared to DC.
4. AC can be controlled much easily compared to DC without much
loss of energy.
DISADVANTAGES OF AC OVER DC
1. AC cannot be used in electrolysis as that of DC.
2. AC is more dangerous than DC.
3. AC will have more magnitude (Positive value) compared to DC
magnitude.

23. The electric circuit designed for the purpose of domestic use
(house, factory, SSI etc) is called domestic electric circuit.
DOMESTIC ELECTRIC CIRCUIT:
The electric circuit is
having,
Live wire ( +ve):
Neutral wire(- ve):
Earth wire (0 V):
S1
S2 S3

24. SUMMARY:
1. Magnetic field and magnetic field line properties.
1. Current carrying conductor and coil possess magnetic properties –
Oersted’s activity
1. Various laws and rules explaining the direction of magnetic field
produced due to current carrying conductor, such as right hand
thumb rule.
1. When current appear to travel in anti clockwise direction in a closed
coil it behave like North pole, if it is clockwise it resembles South pole
of a magnet.
1. The combination of such closed loops form solenoid and when current
is passed through it behaves like bar magnet.

25. 6. The direction of force experienced by current carrying conductor in
uniform magnetic field – Fleming’s left hand rule, its application in
electric motors such as grinder, fan, washing machine etc.
7. Production of induced current/ emf due to relative motion between coil
and magnet – Electromagnetic induction.
8. Current is induced in a coil when subjected rotation in a uniform
magnetic field – Fleming’s right rule
9. Application of EMI in producing current due to various sources – AC
generation in Hydroelectric power plants, wind mill etc.
10. Purposeful use of electricity using domestic electric circuit with
proper safety devices and precautions