Coulomb’s Law of Magnetism

Introduction

We all have heard of magnets and have come across their various types, such as bar magnets and horseshoe magnets. They are available in various shapes such as cylindrical, ring, and spherical magnets. So what are they? Magnets are objects that can attract other objects made of iron, steel, cobalt, and nickel and produce a magnetic field. Magnets are used for multiple purposes such as in toy trains, compasses, in hospitals for NMR and MRI scans, for fridges, for closing doors, in furniture and household appliances, in jewellery, for recycling, and so much more. Read on to know more about the magnetic effects of current and Coulomb’s Law of Magnetism in detail.

Classification of Magnets

Magnets can be classified based on two criteria

• According to their occurrence
• According to their use

According to their occurrence

Magnets occur in two ways. They are either naturally available or artificial/ man-made.

• Naturally occurring magnets – Lodestone, Pyrrhotite, Columbite, and Basalt. Lodestone is the strongest naturally occurring magnet that was first discovered and is also known as magnetite.
• Artificially occurring magnets – Various shapes such as the horseshoe, bar, disc, and ring magnets.

According to their use

• Permanent magnets 
• Temporary magnets 
• Electromagnets
• Permanent magnets

Permanent magnets can emit magnetic fields without requiring any external source of power or magnetism. All naturally occurring magnets are permanent magnets and they never lose their magnetic power once magnetised. Examples: Ceramic or ferrite, Alnico, Samarium Cobalt (SmCo), Neodymium Iron Boron (NIB)

• Temporary magnets

Some magnets can get temporarily magnetised for a short period while acting in the presence of a magnetic field. They lose their magnetic property once the magnetic field is removed. Examples: Iron nails and paper clips.

• Electromagnets

Electromagnets are very strong magnets consisting of a coil of wire wrapped around the metal core made from iron. These magnets depend upon the strength of the electric current and the number of coils of wire. This concept is used in electric motors, televisions, telephones, computers, and other modern devices.

Magnetic effects of electric current

Electric current can exhibit three types of effects, namely, magnetic effect, heating effect, and chemical effect. The magnetic effect is produced when an electric current flows through a wire and generates a magnetic field. This field can be determined by the deflection of a compass. The magnetic field consists of both direction and magnitude. The direction of the magnetic field depends on the direction of flow of the electric current. The magnetic field acts clockwise if the electric current flows from the north to south direction.

Electromagnetic induction

This phenomenon was explained by an English physicist called Michael Faraday. He studied the generation of electric current with the help of a magnetic field and a conductor. The production of electricity due to magnetism, which is termed as induced current, is said to be electromagnetic induction. This phenomenon is used in the conversion of kinetic energy into electrical energy.

Mechanism

When a conductor moves inside a magnetic field or when a magnetic field changes around a conductor, electric current is said to be induced in the conductor. This is opposite to the exertion of force produced by a current-carrying conductor inside a magnetic field. Or, to put it another way, when a conductor is brought in relative motion with relation to a magnetic field, a potential difference gets induced in it.

Solenoid

A solenoid is defined as a coil of wire tightly wound in a spiral form whose diameter is small when compared to its length that converts electrical energy into mechanical work. The solenoid produces a magnetic field similar to a bar magnet. One end of the solenoid acts as the north pole, and the other end acts as the south pole. The magnet formed by the action of the strong magnetic force produced by a solenoid is called an electromagnet.

Coulomb’s law of magnetism

This law states that, if any two magnetic poles of suitable strengths m1 and m2 are held apart by a distance r, then the force of attraction or repulsion between the two poles is said to be directly proportional to the product of their pole strengths and inversely proportional to the square of the distances between them.

The forces of attraction or repulsion exerted between the magnetic poles are also inversely proportional to the absolute permeability “μo” of the surrounding medium.

Coulomb’s Law of magnetism formula can be expressed as

F ∝ m1m2

F ∝ 1/r2

Therefore, F = K (m1m2) / μ0r2

where K is constant.

Conclusion

Magnetic effects of electric current are briefly described in this article. Some properties of magnetic field lines that need to be kept in mind are that they originate from the magnetic north pole and end at the south pole, they are denser near the poles but rarer at other places and do not intersect one another. Coulomb’s law of magnetism describes the electric force between charged objects. It further acknowledges the fact that like poles repel each other, and opposite poles mutually attract.