Magnetic Effects of Electric Current

Introduction

When a compass is brought near an electric current carrying conductor, the needle of compass gets deflected; this happens because of magnetic field produces by electric current. This phenomenon is called magnetic effect of electric current.

Magnet is a substance with a special property or capacity to attract iron and nickel or substances made of iron or nickel towards it. A magnet has two poles, i.e. North Pole and South Pole. When a magnet is suspended free using a thread, its one end points towards north direction and another end points towards south direction. End of magnet that points towards north direction is called North Pole or north seeking and end that points towards south direction is called South Pole or south seeking.

Electricity and Magnetism are related phenomenon. This was first observed by Hans Christian Oersted, a Danish scientist in 1820. In his honour the unit of magnetic field strength is named as Oersted.

Magnetic Field and Field Lines

Magnetic Field: The region surrounding of a magnet, in which the force of the magnet can be observed or detected, is called MAGNETIC FIELD.

Magnetic field has magnitude and direction both, and thus magnetic field is a quantity. Since magnetic field has both magnitude and direction, thus, magnetic field is a quantity.

Field Lines: The magnetic field around a magnet forms a certain pattern; this pattern is called field lines. Field lines are the graphical or pictorial representation of direction and magnitude of magnetic field around a magnet.

Properties of magnetic field and field lines

Direction of magnetic field: The direction of the magnetic field is taken to be the direction in which a north pole of the compass needle moves inside it.

Conventionally, the field lines emerge from North Pole and merge at the South Pole as depicted in figure.

Magnetic field lines are closed curves.

No two field lines cross each other.

The degree of closeness of the field lines shows the strength of magnetic field. This means where field lines are dense, the magnetic strength is greater at that area.

Since, magnetic field lines are densest at poles of magnet (as can be seen in the figure of magnetic lines), thus, magnetic strength is greatest at the poles of magnet.

Electromagnet

When electric current is passed through a conductor, conductor starts behave like a magnet. Thus, an electric carrying conductor is called an ELECTROMAGNET.

Magnetic Field Due to a Current Carrying Conductor

Current carrying conductor may be of two types, i.e. straight conductor and circular loop

Magnetic Field due to Current through a Straight Conductor

When electric current is passed through a straight conductor, it produces magnetic effect. Because of this magnetic field lines are formed around the straight conductor in the form of concentric circles.

The concentric circles are denser near the conductor. This shows that magnetic field is stronger near the conductor and vice versa.

Density of concentric circles increases when magnitude of electric current increases, this shows that magnetic field increases, i.e. becomes stronger with increase in the magnitude of electric current. This means magnetic field varies directly with the magnitude of electric current.

Magnetic field produced by a straight current carrying conductor depends inversely on the distance from it.

Conclusion

• The magnetic field lines are circular and in concentric rings around a straight current-carrying conductor.


• The magnetic field is stronger near the conductor and weakens as we move farther away from the conductor.


• Magnetic field varies directly as the magnitude of electric current.

Right-Hand Thumb Rule

Direction of the magnetic field associated with a current carrying conductor can be understood easily with Right-Hand Thumb Rule.

Right – Hand Thumb Rule states that if one holds a straight current carrying conductor with right hand such that the thumb points towards the direction of current, then fingers will wrap around the conductor in the direction of field lines of the magnetic field.

Magnetic Field due to a Current through a Circular Loop

When electric current is passed through a circular loop, the magnetic field is produced at every point of it is in the form of concentric circles.

Every point of a current carrying conductor in the form of circular loop is act as a straight current carrying conductor.

By moving farther from a point of a current carrying conductor in the form of circular loop, the concentric circles of magnetic field become larger. At the middle point of the center of circular loop, the arcs of these big circles would appear as straight lines.

This means every point on the wire carrying current would give rise to the magnetic field appearing as straight lines at the center of loop.

The direction of magnetic field lines is the same within the loop. The direction of magnetic field is similar as direction of the straight current carrying conductor. The direction of magnetic field can be understood or found using right hand thumb rule.

Conclusion:

• Every point of current carrying conductor in the form of circular loop works similar to a straight current carrying conductor.


• At every point of current carrying conductor in the form of circular loop magnetic field produced is in the form of concentric circle.


• Magnetic field becomes denser near the conductor and rarer by moving farther from the conductor. This means concentric circles due to magnetic field are smaller and very close to each other near the conductor and larger and less dense by moving farther from the conductor.


• At the middle point of the center of circular loop, the arcs of these big circles would appear as straight lines.


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Magnetic field due to a current carrying conductor through a circular loop with more than one turn

Magnetic field produced by a current carrying wire at a given point depends directly upon the current passing through it.

If there are two turns of circular coil, the magnetic field produced by coils will become double as large as that produced by single turn.

And if there are three turns of circular coil, the magnetic field produced by coils will become triple, i.e. three times as large as that produced by single turn.

Thus, if there are n turns of circular coil, the magnetic field produced by coils will become n–times as large as that produced by single turn.

This happens because the current in each circular turn has the same direction and the field due to each turn then just adds up.