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WHAT IS ELECTROMAGNETISM?
The phenomenon where by electricity creates magnetism is known as electromagnetism.
When an insulated wire is wrapped with round an iron nail and the ends of the wire connected to the battery the nail becomes capable of picking up iron fillings paper. This is a simple electromagnet. The nail has been magnetized by the current in the wire.
Disconnecting the wire from the battery the paper clips fall off. The nail looses most of first magnetism when the current is switched off. The passage of electric current along a wire creates a magnetic field around the wire.
The lines of forces due to a straight current carrying wire are circles, center on the wire on the wire. The field is strongest near the wire the direction of the magnetic field is reversed if the direction of the current is reversed.
THE DIRECTION OF THE MAGNETIC FIELD
The direction of the magnetic field is determined by applying the following rules
- Right hand grip rule
States that if you grip a conductor in your right hand the thumb pointing in the direction of the current, the fingers point in the direction of the magnetic field
 2. Maxwell’s screw rule (The corkscrew rule)
States that “if a corkscrew is screwed in the direction of the current in the conductor, the screw rotates in the direction of the magnetic field”
THE DIRECTION OF THE MAGNETIC FIELD IN FIELD IN A SOLENOID
What is a solenoid?
A solenoid is a long coil of wire. The magnetic field lines created by current carrying solenoid are similar to that of a bar magnet.
However unlike a bar magnet the field line pass through the solenoid a long its axis.
RULES
1. Right hand grip rule
If you hold a wire in the right hand and your thumb lies parallel to the wire, the thumb then points in the direction of the flow of current . The remaining fingers point in the direction of the magnetic field.
2. The corkscrew rule
If a right handed cork screw is turned so that its points travel along the current direction, the direction of rotation of the cork screw gives the direction of the magnetic field.
THE FACTORS AFFECTING THE STRENGTH OF A MAGNETIC FIELD AROUND A SOLENOID
- The number of turns (windings)The more the number of turns the stronger is the magnetic field of the solenoid and vice verse
- The amount of current flowing.
- The bigger is the current flowing the stronger is the magnetic field and vice verse.
- Placing a soft iron core along the axis of the solenoid increases the strength of the magnetic field.
FORCE OF A CURRENT CARRYING CONDUCTOR IN A MAGNETIC FIELD
- The force on a conductor of length (L) carrying a current (I) placed perpendicular to the magnetic field is given by Fleming’s left hand rule which states that , if you hold three fingers of your left hand perpendicular to each other such that the forefingers and second finger point in the direction of the magnetic field and the current respectively then the thumb point in the direction of the force (motion) acting on the conductor
 Demonstration
Consider the arrangement below
NOTE;
When the current I flows the conductor AB moves in the direction shown.
FORCE DUE TO TWO PARALLEL CURRENT CARRYING CONDUCTORS
- Consider two parallel current carrying conductors such that the some amount of current, (I) flows through the two conductors since each conductor is a carrying a current, it produces a magnetic field.  Each conductor carries a current in the magnetic field of the in the other conductor. Hence each conductor experiences a force depending on the direction of the currents.
Case 1:Â Â
THE FORCE BETWEEN TWO CURRENT CARRYING CONDUTORS IN THE SAME DIRECTION
                                Â
Observation
- The strips of the conductors attract each other when the currents are flowing in the same direction (because the forces acting on the wires).
Case 2
THE FORCE BETWEEN TWO CURRENT CARRYING CONDUCTORS IN OPPOSITE DIRECTION
                   Â
Observation
The strips of the conductor repel each other where the currents are flowing in the opposite direction.
THE ELECTROMAGNET
•    An electromagnet is a coil of wire wound on a soft iron core controlled by an electric current. When the electric current flows in the iron core the soft iron core is magnetized. When the current is switched off, the magnetism of the electromagnet disappears as it was magnetized temporally, unlike that of a permanent magnet. The soft iron core is magnetized only when the current flows in the coil.
NB;
The poles of the electromagnet are by Maxwell right hand grip rule.
NOTE;
By clock Rule:
When viewing the end of the solenoid, if the current flows in a clockwise direction the end of the soft iron bar is South Pole. (S) If the current flows in a (N) if clockwise direction the end of the soft iron is North Pole (N).
THE DAILY APPLICATIONS OF ELECTROMAGNETS
- The electromagnet is an essential part of many electrical devices including the following;
- Electric bell
- Telephone receiver
- Relay doors
- Scrap yards
- Magnetic tap
AN ELECTRIC BELL
- An electric bell is a bell which uses electricity to function or operate.
Simple construction
Mode of action
When the bell is connected to the power supply the soft iron armature is pulled onto the electromagnet the hammer will strike the gong (hits the gong) and the sound will be heard. This action opens the screw contact and the electromagnet switches off. When the electromagnet is switched off; the soft iron armature returns back to close the screw contact. Again and so the whole cycle repeats itself continuously.
THE TELEPHONE RECEIVER AND LOUD SPEAKER
- The telephone receiver contains a U-shaped magnet formed by placing a short permanent magnet across the ends of the two soft iron bars to exert a pull on a spring magnet alloy diaphragm.
                       Simple construction
     Â
Mode of action
When a varying current is posed through the coil, the magnetic field of the permanent magnet produce a corresponding vibration in the pull of the diaphragm therefore vibrates and reproduces a copy of the sound waves which entered the microphone.
- The electromagnet is used in scraping to lift car bodies or heavy loads. The iron core of the electromagnet must lose its magnetism to release its load when the current is switched off.
- The electromagnets are also used in relays systems and automatic switches.
Simple construction of automatic switches
NB:Â The relay system or automatic switches are used in control circuits to switch the machines on and off. When the current passes through the electromagnet, the iron armature is pulled onto the electromagnet the armature turns about the pivot and closes the switch gap. The relay system or automatic switches are used in making the relay doors or automatic doors in modern offices or banks.
ELECTROMAGNETIC INDUCTION
- Whenever there is relative motion between the magnetic field and the conductor, the electromotive force is induced. The lines of magnetic field are sometimes referred to as magnetic flux. An electromotive force is induced whenever the magnetic flux linking a conductor is cut.
DEMONSTRATION
If a magnet is inserted into a solenoid connected to a galvanometer the current is observed to flow. This process is known as electromagnetic induction. The deflection observed on the pointer of the galvanometer proves that there in is an induced current flowing in the conductor when cut by the magnetic flux.       Â
Deflection is observed
no deflection is observed
