In other words, it is a property of certain substances that attract or repel other objects.
Magnetic effects of electric current
-> When a current flows through the conductor then a magnetic field arises on it. This phenomenon is known as the magnetic effects of electric current.
The direction of the magnetic field is found by Maxwell's right-hand thumb rule or Maxwell's corkscrew rule.
* Magnetic field- The area around a magnet where a magnetic force is experienced is called the magnetic field. It is a vector quantity.
Note:- If we kept any magnetic materials like iron, cobalt, etc. inside or at the surface of the magnetic field then that magnetic materials experience force but if we kept it outside the magnetic field then magnetic materials do not experience any force.
* Magnet- It is defined as a material that can produce its own magnetic field.
Properties of magnets:-
-> Attractive Property– Magnet attracts ferromagnetic materials like iron, cobalt, and nickel.
Note:- Substances which is strongly attracted by the magnetic field and show magnetism even in the absence of a magnetic field called ferromagnetic substances or materials.
-> Repulsive Properties– Like magnetic poles repel each other and unlike magnetic poles attract each other.
-> Directive Property– A freely suspended magnet always points in a north-south direction.
-> Pairproperty- When a magnet is cut into two pieces, both the pieces will have the north pole and the south pole.
Types of Magnets
There are two types of magnets:-
* Permanent magnets- Permanent magnets are those magnets that do not lose their magnetic property once they are magnetized.
-> Normally, we use permanent magnets.
e.g. Refrigerator’s door, Audio speakers, etc.
* Temporary magnets- Those substances that are made of soft metals and only retain their magnetic property in the presence of a magnetic field are called temporary magnets.
When the magnetic field is removed, these materials lose their magnetic property.
e.g. Iron nails, paper-clips, electromagnets, etc.
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Those devices that consisting of a coil of insulated wire wrapped around an iron core that becomes magnetized when an electric current flows through the wire are called electromagnets.
e.g. Hairdryers, CD players, Power drills, Electric mixers, etc.
* Natural magnets- The natural magnets are the one which occurs naturally in nature.
e.g. Lodestone
Lodestone occurs in all types of shapes and has a small magnetic field. To produce a large magnetic field, a large lodestone would be required. This would be very cumbersome (very heavy). So, this arose the development of small but powerful artificial magnets.
Uses:- Mostly used in Navigation as Magnetic needle
* Artificial magnets- An artificial magnet is one that is made by human beings by magnetizing small pieces of iron and nickel.
These are usually made of an alloy called Alnico (aluminium, nickel, cobalt, and iron) and Nipermag (iron, nickel, aluminium, and Titanium).
e.g. Bar magnet, horseshoe magnet, etc.
Uses of magnets
-> in refrigerators
-> in radio and stereo speakers
-> in audio and video cassette players
-> in children’s toys
-> on hard discs and floppies of computers
Magnetic field lines
-> It is an imaginary line at which unit N-pole moves freely. It is also called magnetic lines of force.
Properties of magnetic field lines
* Magnetic lines of force are emitted from the North pole.
* Magnetic lines of force are ends at the south pole.
* Magnetic lines of force are dense at both poles.
* Two magnetic lines of force never intersect each other because of the presence of a unit north pole which travels at each line and hence gets repulsion.
* They always form a closed loop.
-> Outside the magnet, the direction of the magnetic field line is taken from N-pole to S-pole and
Inside the magnet, the direction of the magnetic field line is taken from S-pole to N-Pole.
Important points
-> When the magnetic lines of force are parallel to each other then the magnetic field is uniform. It has the same magnitude and direction.
-> When the magnetic lines of force aren’t parallel to each other then the magnetic field is non-uniform. It has a different magnitude and direction.
-> The point at which magnetic lines of force are far apart than at that point, the magnetic field is very weak.
-> The point at which magnetic lines of force are equal to each other than at that point, the magnetic field is moderate.
-> The point at which magnetic lines of force are very close to each other then at that point, the magnetic field is very strong.
Here, At point A- Very weak magnetic field
At point B- Very large magnetic field
At point C- Moderate magnetic field
Note:- It was Oersted who gave the first evidence of the connection between electricity and magnetism.
This Discovery lead to some of the most fruitful achievements in the areas of industrial and technical development.
-> In Oersted's experiment, when a compass is placed directly over a horizontal wire then some results are found:-
* The needle points North when there is no current.
* The needle swings towards the east when the current flows north.
* The needles swing west when the current flows south.
Note:- When the compass is placed directly under the wire then the needle swings are reversed.
-> Magnetic needles can be deflected only due to the presence of a magnetic field therefore Oersted concluded that a magnetic field is produced around the
current-carrying wire.
This conclusion leads to the magnetic effects of electric current.
The direction of deflection of the needle can be determined by the following rules:-
(i) Snow Rule- It states that if the current is flowing in an electric circuit from South to North direction and
the magnetic compass is placed over the conducting wire, then the needle of the compass deflects in the West direction.
(ii) Ampere’s swimming Rule- It states that if a man swims along the
current-carrying wire, such that his face is always towards the magnetic needle through which the current is entering his feet and leaving from his head, then the north pole of the magnetic needle is always deflected towards his left hand.
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