Download Magnetic Effect of Electric Current

Magnetic Effect of Electric Current
Electromagnetic Effect
Magnet A substance which has the property of attracting other substances like iron filings and points in the
north south direction when suspended freely is called a magnet.
Similar to other effects; electric current also produces magnetic effect. The magnetic effect of electric
current is known as electromagnetic effect.
It is observed that when a compass is brought near a current carrying conductor the needle of compass gets
deflected because of flow of electricity. This shows that electric current produces a magnetic effect.
Properties of magnet:
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
A free suspended magnet always point towards north and south direction.
The pole of a magnet which points toward north direction is called north pole or north seeking.
The pole of a magnet which points toward south direction is called south pole or south seeking.
Like poles of magnets repel each other while unlike poles of magnets attract each other.
Magnetic field and Field Lines
 Magnetic field The space around a magnet in which the force of attraction and repulsion due to it
can be detected is called the magnetic field.
 Magnetic field lines The curved paths along which the north pole of the compass needle moves in a
magnetic field are called magnetic field lines. Magnetic field lines are used to represent a magnetic
field.
The influence of force surrounding a magnet is called magnetic field. In the magnetic field, the force exerted
by a magnet can be detected using a compass or any other magnet.
The imaginary lines of magnetic field around a magnet are called field line or field line of magnet. When
iron fillings are allowed to settle around a bar magnet, they get arranged in a pattern which mimicks the
magnetic field lines. Field line of a magnet can also be detected using a compass. Magnetic field is a vector
quantity, i.e. it has both direction and magnitude.
Direction of Field Line:- Outside the magnet, the direction of magnetic field line is taken from north pole to
South Pole. Inside the magnet, the direction of magnetic field line is taken from south pole to north pole.
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Strength of magnetic field: The closeness of field lines shows the relative strength of magnetic field, i.e.
closer lines show stronger magnetic field and vice-versa. Crowded field lines near the poles of magnet show
more strength.
 Properties of magnetic field lines
1.The magnetic field lines never intersect each other because if they do so it means that at that
point the compass needle would point towards two directions which is not possible.
2. They emerge at North Pole and merge at South Pole.
3. They are crowded near the poles and are far apart near the middle.
4. These are directed from North Pole to South Pole outside the magnet and from south to North
Pole inside the magnet.
2. Oersted Experiment
On passing the current through the copper wire XY in the circuit, the compass needle which is placed near
the conductor gets deflected. If we reverse the direction of current, the compass needle deflect in reverse
direction. If we stop the flow of current, the needle comes at rest.Hence, it conclude that electricity and
magnetism are linked to each other. It shows that whenever the current will flow through the
conductor, then magnetic field around. it will develope
 Magnetic field due to current through a straight conductor:A current carrying straight conductor has magnetic field in the form of concentric circles; around it.
Magnetic field of current carrying straight conductor can be shown by magnetic field lines.
The direction of magnetic field through a current carrying conductor depends upon the direction of flow of
electric current. The direction of magnetic field gets reversed in case of a change in the direction of electric
current.
Let a current carrying conductor be suspended vertically and the electric current is flowing from south to
north. In this case, the direction of magnetic field will be anticlockwise. If the current is flowing from north
to south, the direction of magnetic field will be clockwise.
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 Right Hand Thumb Rule: The direction of magnetic field; in relation to direction of electric current
through a straight conductor can be depicted by using the Right Hand Thumb Rule. It is also known
as Maxwell’s Corkscrew Rule.
If a current carrying conductor is held by right hand; keeping the thumb straight and if the direction of
electric current is in the direction of thumb, then the direction of wrapping of other fingers will show the
direction of magnetic field.
As per Maxwell’s corkscrew rule, if the direction of forward movement of screw shows the direction of
current, then the direction of rotation of screw shows the direction of magnetic field.
 Properties of Magnetic Field lines due to straight conductor:
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

The magnitude; of magnetic field increases with increase in electric current and decreases with
decrease in electric current. (B ά I)
The magnitude of magnetic field; produced by electric current; decreases with increase in distance
and vice-versa. The size of concentric circles of magnetic field lines increases with distance from the
1
conductor, which shows that magnetic field decreases with distance. ( Bα r )
Magnetic field lines are always parallel to each other.
No two field lines cross each other.
Magnetic field due to current through a circular loop:
 Magnetic field due to current carrying circular loop or coil
When the current is passed through circular loop or coil, the lines of force are circular near the
wire but straight and parallel near the centre of loop or coil.
In case of a circular current carrying conductor, the magnetic field lines would be in the form of concentric
circles around every part of the periphery of the conductor. Since, magnetic field lines tend to remain closer
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when near the conductor, so the magnetic field would be stronger near the periphery of the loop. On the
other hand, the magnetic field lines would be distant from each other when we move towards the centre of
the current carrying loop. Finally; at the centre, the arcs of big circles would appear as a straight lines.
Factors affecting magnetic field due to current carrying circular loop or coil.
Directly proportional to the current passing through it. I
Inversely proportional to the radius of loop r
Number of loops N
The direction of magnetic field can be identified using Right Hand Thumb’s Rule. Let us assume that the
current is moving in anti-clockwise direction in the loop. In that case, the magnetic field would be in
clockwise direction; at the top of the loop. Moreover, it would be in anticlockwise direction at the bottom of
the loop.
Clock Face Rule: A current carrying loop works like a disc magnet. The polarity of this magnet can be
easily understood with the help of clock face rule. If the current is flowing in anti-clockwise direction, then
the face of the loop shows north pole. On the other hand, if the current is flowing in clockwise direction,
then the face of the loop shows south pole.
Magnetic field and number of turns of coil:
Magnitude of magnetic field gets summed up with increase in the number of turns of coil. If there are ‘n’
turns of coil, magnitude of magnetic field will be ‘n’ times of magnetic field in case of a single turn of coil.
 Magnetic Field due to a current in a Solenoid:
Solenoid is the coil with many circular turns of insulated copper wire wrapped closely in the shape of
cylinder.
A current carrying solenoid produces similar pattern of magnetic field as a bar magnet. One end of solenoid
behaves as the north pole and another end behaves as the south pole. Magnetic field lines are parallel inside
the solenoid; similar to a bar magnet; which shows that magnetic field is same at all points inside the
solenoid.
Similarities and differences between Solenoid and Bar Magnet
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Similarities:
1. Both possess property of attraction (attracts iron fillings) and directive property (when suspended
freely sets itself in the North- South Direction)
Differences
1. Polarity of solenoid can be changes by changing the direction of current but that of bar magnet is not
possible
2. Strength of solenoid can be changed but that of bar magnet is not possible
Electromagnet: By producing a strong magnetic field inside the solenoid, magnetic materials can be
magnetized. Magnet formed by producing magnetic field inside a solenoid is called electromagnet.
Difference between electromagnet and Permanent Magnet.
Electromagnet
Temporary magnet as it is demagnetised by
stooping current though it
Soft iron core is used
Produces strong magnetic field
Strength can be changed changing current
polarity can be changed by reversing
direction of current
Permanent Magnet
Permanent Magnet as it can not be
demagnetised
Steel is used
Produces weak magnetic field
Strength can not be changed
polarity can not be changed
 Force on a current carrying conductor in a magnetic field.
Andre Marie Ampere (1775-1836) suggested that the magnet also exert an equal and opposite force on the
current carrying conductor. We will observe that the rod will displace i.e. the rod will experience a force,
when it is placed in magnetic field, in a perpendicular direction to its length.– The direction of the exert
force will be reversed if the direction of current through the conductor is reversed.– If we change the
direction of field by inter changing the two poles of the magnet, again the direction of exert force will
change.
– Therefore the direction of exerted force depends on
(1) direction of current
(2) direction of magnetic field lines.
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Left Hand Fleming Rule
According to this rule, stretch thumb, forefinger and middle finger of your left hand such that
they are mutually perpendicular to each other.If fore finger represent direction of magnetic field &
middle finger represent direction of current, then thumb will point in the direction motion or force
acting on the conductor.
The factors affecting magnitude of force exerted:
1. Magnitude of the magnetic field(B) Fα B
2. Magnitude of current (I) F α I
3. Length of the conductor (l) F α l
Force will be maximum when current carrying conductor is placed
perpendicular to the magnetic field.
Electric Motor:
It is device used for converting electrical energy into mechanical energy. Used in electric appliances like
fan, A.C., cooler, washing machines, mixers, blenders.
Principle: when a coil carrying current is placed in a magnetic field, it experiences a torque, as a result of
torque the coil begins to rotate.
Construction: It consists of 5 parts:
1. Armature: Armature ABCD consists of large no. of turns of copper wire wound over a soft iron.
2. Field Magnet: permanent magnet NS
3. Split rings/ commutator(P,Q) two halves of same metallic ring to which the ends of armature coil are
connected which also rotate the armature.
4. Brushes(X,Y): two metal plates/ carbon rods X, Y which are so fixed that they constantly touch with
rings.
5. Battery: battery consists of few cells and is connected across brushes, current is passed through
brushes to split rings to armature.
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Working:
a) Let us suppose that battery sends current as shown in fig.
Applying Flemings left hand rule , we find that AB experiences a force which is acting downwards
and arm CD experiences a force which is acting upward. These two forces form a couple which
make armature rotate in anticlockwise rotation.
b) After armature completes half revolution , the direction of current in the arm AB & CD reversed.
Now the arm CD experiences downward and arm AB experiences upward force. The armature
turns continuous to rotate in the same direction.( anticlockwise)
Speed of rotation can be increased by i) increasing strength of current
ii) increasing strength of magnet iii) increasing no of turns in the coil of armature.
Commutator: is a device that reverses the direction of flow of current through the circuit. Split
ring in electric motor works as commutator.
Electromagnetic Induction
The phenomenon of generation of an electric current in a circuit from magnetic effects i.e. by changing
magnetic field lines linked with it is called as electromagnetic induction.
Faraday’s experiment for electromagnetic induction:
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Experiment setup used for faraday consists of few turns of wire. A sensitive galvanometer G is connected in
series with coil. Faraday’s observation are as below:
i)
ii)
iii)
iv)
v)
When a magnet is stationary there is no deflection in galvanometer G
When N-pole of magnet is brought towards coil, the current flows in the coil and galvanometer
shows deflection towards right.
If the motion of magnet is stopped, galvanometer shows no deflection, thus current flows in the
coil as long as magnet is moving.
Now magnet is moved away from coil current flows in the opposite direction, and galvanometer
shows deflection towards left.
If S-pole is brought towards or moved away from the coil, the deflection in galvanometer is in
opposite direction as observed in case of N-pole movement.
Conclusion:
i)
ii)
iii)
Galvanometer shows deflection only when there is a motion between coil and the magnet.
Direction of deflection is reversed if the direction of relative motion of coil and magnet is
reversed.
The deflection in galvanometer is increases if the magnet and the coil are rapidly moved w.r.t
each other.
Reason for electromagnetic induction: current is induced in the coil because of change in magnetic
field lines (flux) associated with coil.

Different ways of producing induced current
i) By relative motion between magnet and coil
ii) By relative motion between coil and current carrying conductor
iii) By changing the current in a conductor placed near the coil.
Faraday’s law of electromagnetic Induction:
i) Whenever there is change in magnetic flux linked with a coil , an electric current is induced. The
induced potential difference lasts as long as there is a change in magnetic flux linked with the coil.
ii) Magnitude of induced current is directly proportional to the rate of change of magnetic flux.
Direction of induced current: (Flemings right hand rule):
If the magnetic poles are fixed and if we move the coil perpendicularly with the direction of magnetic
field then the direction of induced current is found by Flemings right hand rule.
Rule: stretch the thumb , forefinger and middle finger of right hand so that they are mutually
perpendicular to each other. If the forefingers points In the direction of magnetic field, thumb points
in the direction of motion of coil, then the middle finger points in the direction of induced current.
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Electric Generator(AC & DC)
A generator or dynamo is a machine used for generating electric current by converting mechanical
energy into electrical energy.
Types of currents:
 AC- alternating current
2. DC- direct current
1. AC- an electric current which changes its direction after certain fixed interval of time is called
alternating current.
2. Frequency of AC- number of cycles completed by AC in one second is called its frequency.
3. Frequency of AC In India is 50hz which means that its polarity changes after 1/100 s, as it
complete its one cycle in 1/50 s.
 DC- an electric current which always flow in the same direction is called Direct Current.
 Advantages of AC over DC:
1. AC at any desired voltage can be obtained by use of transformers.
2. Cost of transmission of AC is low
3. Power wastage in AC transmission is negligible.
4. AC can be controlled and energy loss is very small but DC can be controlled by only resistances
which involves huge energy loss in form of heat.
5. AC machines are durable and do not need much maintenance.
Alternating Current (AC) generator:
Function: it converts mechanical energy to electrical energy.
Principle: whenever in a closed circuit the magnetic field linked to it changes , induced current is produced in
it.
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Construction:
1. Armature: it is the coil consisting large number of turns of insulated copper wire wound around soft
iron core. It revolves around the axle between two poles of the magnet.
2. Field magnet: it is a permanent magnet in small generators and electromagnet is used in big
commercial generators.
3. Slip rings: (R1 and R2) are two hollow metallic rings held at different heights. The end D of armature
coil is connected to R1 and end C of the coil is connected to R2 through R1.these rings rotate as the
coil rotates.
4. Brushes (B1 and B2): these are flexible metallic plates or carbon rods. B1 is in constant touch with ring
R1 and B2 is in constant touch with ring R2. With the help of these brushes induced current is passed
from armature through rings to external circuit of resistance R and galvanometer G. Brushes are
stationary.
Working: as the armature rotated about an axis , magnetic flux linked with the armature changes and
induced current is produced.
a) Suppose the armature ABCD is rotated anticlockwise, so that arm AD moves downwards and BC
moves upwards. Applying Flemings right hand rule, we find that induced current is produced in the
armature from A to D and Cto B, due to which Galvanometer shows deflection towards right.
b) When armature turned through 180° it occupies position as shown in fig B , with the armature
rotating in the same direction, BC moves downwards and AD moves upwards, again applying Flemings
right hand rule we find that induced current in external circuit flows in opposite direction due to which
galvanometer shows deflection towards left.
c) Thus we see that direction of induced current changes after every half rotation of armature. Hence
induced current is alternating in nature.
Direct Current (DC) generator:
Principal , construction and working of DC generator is same as that of AC generator except use sliding
contact or split rings in place of slip rings as shown in fig below.
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Working:
a)The armature is moved in clockwise direction, so that arm AD moves upward and arm BC moves
downwards, thus by applying Flemings right hand rule, current is induced in the armature as shown in
fig A. and galvanometer shows deflection towards left.
b) after armature rotated at 180° ( half rotation), it occupies the position as shown in fig B. , with
armature in the same direction but now BC moves upward and AD moves downwards. Applying
Flemings right hand rule, current is induced in the direction shown in fig b.
c) the direction of induced current does not change through out complete rotation of armature i.e
current in the circuit is always in the same direction, hence current induced is of direct in nature.
Domestic Electric Circuits :–
In our homes, the electric power supplied is of potential difference V = 220V and frequency 50Hz.
It consist of three wires :–
(1) Wire with red insulation cover – LIVE WIRE (POSITIVE)Live wire is at high potential of 220V
(2) Wire with black insulation cover – NEUTRAL WIRE (NEGATIVE)Neutral wire is at zero potential
Therefore, the potential difference between the two is 220V.
(3) Wire with Green insulation cover – EARTH WIRE
it is connected to a copper plate deep in the earth near house.The metallic body of the appliances is
connected with the earth wire as a safety measure.
Function–
Earth wire provide a low resistance to the current hence any leakage of current to the metallic body of the
appliances, keep its potential equal to that of earth. That means zero potential and the user is saved from
severe electric shock.
Point to be noted in domestic circuit
(1) Each appliance has a seperate switch of ON/OFF
(2) In order to provide equal potential difference to each appliance, they should
be connected parallel to each other. So that they can be operated at any time.for high power appliances
(3) We have two electric circuit in our home Other circuit consist of current 5A for low power appliances.

Short Circuiting –
Due to fault in the appliances or damage in the insulation of two wires,the live and neutral wire comes in
contact with each other. the circuit will offer zero or negligible resistance to the flow of current. Due to low
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resistance, large amount of current will flow.According to Joule’s law of heating effect (HaI2) heat is
produced in live wire and produces spark, damaging the device and wiring.

Overloading–
Overloading can be caused by (1) Connecting too many appliances to a single socket or (2) accidental rise
in supply voltage if the total current drawn by the appliances at a particular time exceeds the bearing
capacity of that wire, it will get heated up. This is known as overloading.
Fuse : a safety device can prevent the circuit from overloading and short circuiting.it is used in series
to limit the current in a circuit so that it easily melts due to overheating when excessive current passes
through it.
Properties of wire used for fuse:
1. It should have low melting point
2. It is always connected in live wire and at the beginning of the circuit and must have current capacity
less than maximum current that the circuit should withstand.
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