Magnetic Effect of Electric Current

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CHAPTER - 13
MAGNETIC EFFECTS OF ELECTRIC CURRENT

1) Magnetic field and Field lines:-
a) Magnetic field :-
The region around a magnet where the force of attraction or repulsion can be detected is called magnetic field. Magnetic field around a magnet can be detected by using a magnetic compass. b) Magnetic field lines:-

Magnetic field lines are the paths around a magnet along which the north pole of a magnetic compass needle tends to move.

The magnetic field lines around a magnet can be observed by sprinkling iron filings around a magnet. It can also be observed by moving a magnetic compass around a magnet. i) The magnetic field lines emerge at the North Pole and merge at the South Pole. ii) The magnetic field lines are closer at the poles.

iii) The magnetic field lines do not intersect each other.
2) Magnetic field due to a current carrying conductor:-
If a magnetic compass is placed near a conductor carrying current (wire), the needle is deflected. This shows that a conductor carrying current has a magnetic field around it. If the direction of the current is from north to south, the deflection of the magnetic needle is towards the east. If the direction of the current is from south to north, the deflection of the needle is towards the west. The magnetic field around a current carrying straight conductor is in concentric circles. It can be observed by passing a current carrying straight conductor through a cardboard and sprinkling iron filings on it.

Right hand thumb rule:-

The direction of the magnetic field around a conductor is given by the Right Hand Thumb Rule.

It states that ‘ If a current carrying conductor is held in the right hand such that the thumb points in the direction of current, then the fingers wrapped around the conductor shows the direction of the magnetic field ’.

3) Magnetic field due to a current through a
circular loop:-
When current is passed through a circular conductor (loop) the magnetic field produced is in the form of concentric circles around the conductor. Towards the centre the arc of the circles become larger and appears as straight line. 4) Magnetic field due to current in a solenoid:-

A solenoid is a circular coil of wire in the shape of a cylinder. When current flows through a solenoid, it behaves like a bar magnet. The end of the solenoid behaves like the North and South poles of a magnet. The magnetic field produced by a solenoid is similar to the magnetic field produced by a bar magnet. The strength of the magnetic field depends upon the strength of the current and the number of turns of the coil.

5)Electromagnet:-
A strong magnetic field inside a solenoid can be used to magnetize a piece of magnetic material like a soft iron when placed inside the coil. Such a magnet is called an Electromagnet. If electric current is passed through a wire wound around a piece of soft iron, it behaves like a magnet. Such a magnet is called an electromagnet.

6) Force on a conductor carrying current in a magnetic field A.M.Ampere suggested that if a current carrying conductor produces a magnetic field and exerts a force on a magnet, then a magnet should also exerts a force on a current carrying conductor.

Eg :- If an aluminium rod is suspended horizontally by a wire between the poles of a horse shoe magnet and current is passed through the wire, then the aluminium rod is displaced. If the direction of current is reversed, the direction of displacement is also reversed. The force exerted is maximum if the conductor is perpendicular to the magnetic field.

Fleming’s Left Hand Rule

The direction of force (motion) of a current carrying conductor in a magnetic field is given by Fleming’s Left Hand Rule.

It states that ‘ If we hold the thumb, fore finger and middle finger of the left hand perpendicular to each other such that the fore finger points in the direction of magnetic field, the middle finger points in...
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