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Magnetic Effects of current

 So , our first question that arises in our mind is what is Magnetic effects of current

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When there is an electric current passing through a circuit then the circuit experiences magnetic field. This property of electric current is called Magnetic effects of current.

Magnetic field

The particular area on which the magnetic force is exerted by a magnet is called its magnetic field.

Magnetic field around a bar magnet

magnetic-field-cordelia-molloy

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.

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.
Magnetic field Due to a Current Carrying Conductor:

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: It tells us that if we hold a current carrying conductor in our right hand palm in such a way that our thumb points towards the direction electric current then magnetic field produced will be in the direction of the curl of our fingers.  If the current is in the upward direction then the magnetic field produced will be in the anticlockwise direction and if it is in downward direction then the direction of magnetic field produced will be vice-versa of the above situation.

Maxwell’s corckscrew rule
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.

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Properties of Magnetic Field:
•The magnitude of magnetic field increases with increase in electric current and decreases with decrease in electric current.
•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 conductor, which shows that magnetic field decreases with distance.
•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:

10_physics_magnetism_fig_5

In case of a circular current carrying conductor, the magnetic field is produced in the same manner as it is in case of a straight current carrying conductor.

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 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.

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.

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.

Fleming’s Left Hand Rule:

If we stretch  our middle finger , fore-finger and thumb of our left hand  in such a way that they  are mutually perpendicular to each other. If middle finger points towards the direction of flow of electric current , fore-finger points towards the direction of magnetic field and the thumb points towards the direction of motion of conductor or force.

Many devices, such as electric motor, loudspeaker, etc. works on the Fleming’s left Hand Rule.

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Electric Motor:

electric motor

Electrical energy is converted into mechanical work by using an electric motor. Electric motor works on the basis of rule suggested by Marie Ampere and Fleming’s Left Hand Rule.

Principle

A motor works on the principle that when a coil is placed between the magnetic field then it experiences torque. Torque is nothing but the tendency to rotate.

Working of a Motor

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We are taking a rectangular coil of ABCD that is placed between a magnet of North pole and south pole. Now the side AB is attached with its commutator(split ring) P. Commutator is a device which reverses the direction of current. The commutator P is attached with the carbon brush X and commutator Q is attached with carbon brush Y that is further attached with the side CD of rectangular coil ABCD. Carbon Brush which make a contact with the split ring so that the coil keeps on getting current for rotation.

Now when the current passes brushes to split ring and then to the coil AB and CD then after applying Flemings left hand rule the direction of magnetic field is from North pole to south pole that is in the left to right and the current is flowing in AB produces a force in vertically downward direction whereas the side of coil CD produces a force in the vertically upward direction. This helps the coil ABCD to rotate in the anticlockwise direction. Now, the coil CD comes at the position of AB .While rotating the coil reaches a vertically position where the commutator link is broken and current supplied through the carbon brushes P and Q are cut off. But due to moving of coil it gains momentum and goes beyond the vertical position and again it comes in contact with split rings and receives current to rotate again and again .

Now in this a shaft is connected  with the coils to a dynamo which help in converting electrical energy to mechanical work.


 

Electromagnetic Induction

Michael Faraday, an English Physicist is supposed to have studied the generation of electric current using magnetic field and a conductor.

When there is a relative motion between coil and a magnet then an instantaneous amount of current is produced and this instantaneous current is called induced current. This phenomenon is called Electromagnetic induction.

Electromagnetic induction can be explained with the help of Fleming’s Right Hand Rule. If the right hand is stretched in a way that the index finger, middle finger and thumb are in mutually perpendicular directions, then the thumb shows the direction of movement of the conductor, index finger shows the direction of magnetic field and the middle finger shows the direction of induced current in the conductor. The directions of movement of conductor, magnetic field and induced current can be compared to three mutually perpendicular axes, i.e. x, y and z axes.

The mutually perpendicular directions also point to an important fact that the when the magnetic field and movement of conductor are perpendicular, the magnitude of induced current would be maximum.

Electromagnetic induction is used in the conversion of kinetic energy into electrical energy.

Electric generator:

electric generator

The structure of electric generator is similar to that of an electric motor. In case of an electric generator a rectangular armature is placed within the magnetic field of a permanent magnet. The armature is attached to wire and is positioned in way that it can move around an axle. When the armature moves within the magnetic field an electric current is induced. The direction of induced current changes, when the armature crosses the halfway mark of its rotation. Thus, the direction of current changes once in every rotation. Due to this, the electric generator usually produces alternate current, i.e. AC. To convert an AC generator into a DC generator, a split ring commutator is used. This helps in producing direct current.

AC and DC current:

AC – Alternate current: Current whose direction reverses after every equal interval of time. In India, most of the power stations generate alternate current. The direction of current changes after every 1/100 second in India, i.e. the frequency of AC in India is 50 Hz. AC is transmitted upto a long distance without much loss of energy is advantage of AC over DC

DC – Direct current: Current that flows in one direction only is called Direct current. Electrochemical cells produce direct current.