# UNIT OF MAGNETIC FIELD

## Magnetic Field

In general terms, a magnetic field refers to the area surrounding a magnet or a moving electric charge within which the magnetic force is experienced. The force of magnetism acts in a direction perpendicular to that of the direction of the velocity of a moving charge in a magnetic field. Also, it acts perpendicular in the direction of the magnetic field itself. The magnetic field produced by a permanent magnet exerts a pulling force on ferromagnetic materials like iron and will either repel or attract another magnet depending on the orientation of the magnets, that is, if the facing poles of the magnets are the same or opposite (same poles repel, opposite poles attract). Moreover, a magnetic field that varies with location exerts a magnetic force that affects non – magnetic materials by changing the movement of the electrons in their outermost valence shells.

The term magnetic field can be used to refer to two similar, but different types of vector fields indicated by using the symbols H and B. H, which denotes the magnetic field strength is expressed using the SI base units of ampere per meter (A/m). B, which denotes the magnetic flux density of the magnetic field, is expressed in tesla (T), the SI base unit of which is kilogram per second 2 per ampere; this is equal to newton per meter per ampere. B and H are different from each other in the way they induce the force of magnetization.

Magnetic fields result from the movement of electrical charges and the intrinsic magnetic moments of elementary particles due to those particle’s spin, which is a fundamental quantum property. The components of the electromagnetic force, which is one of the four fundamental forces of nature, are magnetic fields and electric fields, both of which are interrelated. Magnetic fields play a huge role in modern engineering and technology. Motors make use of rotational magnetic fields to convert electrical energy to mechanical energy and mechanical energy to electrical energy in the case of generators.

## Units of Magnetic Field

We have already established that the two kinds of vector fields, B and H, are commonly referred to as the magnetic field’s strength and the magnetic field’s density. H – field is very similar to B – field except it is the equivalent of B – field measured inside a material. However, they also differ from each other in the way they are measured. B - field is expressed in terms of tesla and is denoted by the symbol T whereas H - field is measured and expressed in terms of amperes per meter which is denoted as A/m. A flux density of one tesla is equal to one weber per square meter, which is denoted as wb/m 2 . In accordance with Lorentz Force law, F = qvB where

• F is the force of magnetization
• q is the electric charge
• v is the velocity of the particles
• B is the magnetic field

Thus, it can be said that a particle of a charge of 1 coulomb, moving at a direction perpendicular (90 0 ) to and in a magnetic field of magnitude 1 tesla, at a speed of 1 m/s, experiences a force of magnitude 1 newton. The unit of B – field, tesla, can also be expressed as T = V.s/ m 2 = N/A. m = J/A.m 2 = H.A/ m 2 = Wb/ m 2 = Kg/ C.s = N.s/ C. m = Kg/ A. s 2 where

• V = volt, unit for voltage
• s = second, unit of time
• m = meter, unit of distance
• N = newton, unit of force
• A = ampere, unit of electric current
• J = joule, unit of energy
• H = henry, unit of electrical inductance
• Wb = weber, unit of magnetic flux
• Kg = kilogram, unit of mass
• C = coulomb, unit of charge

Besides the SI system, the B – field in the CGS system is expressed in a smaller unit of the magnetic field known as gauss, which is denoted by the symbol G. Tesla and gauss are related using the expression 1 T = 10,000G. Additionally, the H-field in the CGS system is expressed in terms of oersted (Oe), which is identical to 1 dyne per maxwell. Equivalent values of tesla and other units in terms of each other are given below.

• 1 T = 10,000 (or 10 4 ) G (Gauss) or alternatively 10 kG = 1 T (tesla)
• 1 G = 10 −4 T = 100 μT (microtesla)
• 1 T = 1,000,000,000 (or 10 9 ) γ (gamma) or alternatively 1 γ = 1 nT (nanotesla)
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