Magnetism and electromagnet

 magnets: Magnet is a force that acts on some materials and not on other materials. Physical devices which possess this force are called magnets. Magnets attract iron and steel, and when free to rotate, they will move to a fixed position relative to the north pole.

the substance which attracted the magnetic  materials toward that's know as magnet.

following character of a good magnet material

-- magnet attracted the magnetic materials .

-- magnet has two magnet poles North Pole (N) and south pole (S) .

-- magnet poles is not separated .

-- same and equal strength of both magnet poles .

-- center of the magnet is no force.

-- in  Magnet like poles are repel each other and attracted each other unlike poles . 

-- magnet is freely suspended in air , it indicates north and south .

TYPES OF MAGNET:

there are two types of magnet : 

1) NATURAL MAGNET

2) ARTIFICIAL MAGNET

NATURAL MAGNET : an ancient era some black hard materials was founded in Magnetia,  This materials was called lodestone and  a property of attracting small pieces of iron  on it was know as magnetite. Afterward due to property of attracting it is popular with name of magnet. Because  this reason its called natural magnet.

ARTIFICIAL MAGNET : The magnet whose prepared by artificial method that's called artificial magnet 

there are two types of artificial magnet : 

-- TEMPORARY MAGNET

-- PARMANENT MAGNET

-- TEMPORARY MAGNET :  a piece of magnetic material is placed in a strong magnetic field of solenoid it becomes magnetised by induction. The soft iron  becomes a temporary magnet as long as the current continues to flow in the solenoid it self .  source producing as soon as the mag- netic field is removed, the soft iron piece will loose its magnetism.

-- PARMANENT MAGNET :  steel is substituted for soft iron in the same inducing field as in the previous case, due to the residual magnetism, the steel will become a perma- nent magnet even after the magnetising field is re- moved. This property of retention is termed retentivenes. Thus, permanent magnets are made from steel, nickel, ALNICO, TUNGSTEN all of which have higher retentive- ness.

the magnet which attain the magnetic properties for short periods is known as temporary magnet .

Properties of a magnet The following are the properties of magnets.

ATTRACTIVE PROPERTY: 

 the property of magnet attracting magnetic substances  and its power of attraction is greatest at its poles.

DIRECTIVE PROPERTY: 

 its poles will always tend to set themselves in the direction of north and south. 

INDUCTION PROPERTY: 

A magnet has the property of producing magnetism in a nearby magnetic substance by induction.

POLES-EXISTING PROPERTY: 

A single pole can never exist in a magnet. If it is broken into its molecules, each molecule will have two poles. 

DEMAGNETISING PROPERTY: 

If a magnet is handled roughly by heating, hammering,  it will lose its magnetism.

PROPERTY OF STRENGTH: Every magnet has two poles. The two poles of a magnet have equal pole strength.

SATURATION PROPERTY: 

If a magnet of higher strength is further subjected to magnetization, it will never acquire more magnetization due to its being already saturated.

PROPERTY OF ATTRACTION AND REPULSION: 

Unlike poles (i.e. north and south) attract each other, while like poles  repel each other.

METHODS OF MAGNETIZATION

There are three principal methods of magnetizing a material.

Touch method

By means of electric current

 Induction method.

TOUCH METHOD: This method can be further divided into:

single touch method

double touch method

 divided touch method

SINGLE TOUCH METHOD: 

In the single touch method, the bar of steel is  magnetized is rubbed with either of the magnet poles , keeping the other pole away from it. Rubbing is done only in one direction as shown in . The process should be repeated many times for inducing magnetization of the bar.

DOUBLE TOUCH METHOD:

 In this method the steel bar is magnetized is placed over the two opposite pole ends ofA a magnet, and the rubbing magnets are placed together over the centre of the bar with a small wooden piece in between, as shown in . They are never lifted off the surface of the steel bar, but rubbed again and again from end to end, finally ending at the centre where the rubbing was started.

ELECTRO MAGNET :

 In the year 1819, Oersted discovered that an electric current always accompained by a magnetic field.On placing a wire carrying current parallel to a magnetic needle, it is found that the needle gets, deflected as if acted upon by a magnet

Direction of deflection depends upon the direction of the current.

Deflection can be increased by

1. Bringing the needle closer to the conductor.

2. Increasing the current.

From above experiment it follows that every conductor carrying current is surrounded by a magnetic field. The magnetic field exists in circles above the conductor. The circles have their centres at the centre of the conductor a their planes are perpendicular .

 (i) that conductor itself is not magnetised. (ii) the field strength decreases as the distance from the conduct increases.

A definite relation exists  between the direction of the current in conductor the direction of the magnetic field surrounding the conductor. There are rules by which this relation may be remembered.

1. Right Hand Gripping Rule. Grip the conductor in the right hand thumb in the direction of the current as shown. Then the direction of line of flux coincides with the direction in which the fingers are bent round the e as show 

Symbols given below are used to show the current direction and its Magnetic field direction. (+) means current going away from you or current goes into the plan paper.

(•) means current coming towards you or current coming out of the plan of paper.

(i) Ampere Rule

(ii) Cork Screw Rule.

(1) Ampere Rule. It is used for finding the direction of lines of  force around a wire-carrying current. It states that if an observer imagines himself in the electric circuit with the current flowing in the direction from his feet to his head, then on facing the compass needle, the north will be deflected towards his left hand. 

( ii )CorkScrew Rule. It is used for finding the direction of lines of around a wire carrying current.

Imagine a right-hand screw to be along the wire carrying current. Then the flux surrounding the conductors bears the same relation to the flow of current as the direction of rotation of a right handed screw bears to the direction of advancement of its points .

Field to Circular Coil:If the conductor is bent so as to form a circular loop and it carries current in the direction . it will give magnetic field .