Electromagnetism

Electromagnetism

Magnets • A magnet from Greek word (μαγνήτιςλίθοςmagnḗtislíthos, "Magnesian stone"). • Magnets have been known for centuries. • The Chinese and Greeks knew about the “magical” properties of magnets. • The ancient Greeks used a stone substance called “magnetite.” They discovered that the stone always pointed in the same direction. Later, stones of magnetite called “lodestones” were used in navigation. • An object that is surrounded by a magnetic field and that has the property, either natural or induced, of attracting iron or steel.

William Gilbert, an English physician, first proposed in 1600 that the earth itself is a magnet, and he predicted that the Earth would be found to have magnetic poles.

What is Magnetism • Magnetism is the properties and interactions of magnets. • The earliest magnets were found naturally in the mineral magnetite which is abundant the rock-type lodestone. These magnets were used by the ancient peoples as compasses to guide sailing vessels. • Magnets produce magnetic forces and have magnetic field lines.

Magnets have two ends or poles, called north and south poles. At the poles of a magnet, the magnetic field lines are closer together. Unlike poles of magnets attract each other and like poles of magnets repel.

The Earth is like a giant magnet! • The nickel iron core of the earth gives the earth a magnetic field much like a bar magnet.

History • In 1820, Hans Christian Oersted discovered the connection between electricity and magnetism when he observed the magnetic needle of a compass was deflected by an electric current in a nearby wire. • In 1831, Michael Faraday showed that a changing magnetic field can induce a current in a circuit. • In 1860, James Clerk Maxwell predicted that a changing electric field has an associated magnetic field and wrote the mathematical equations that describe the force of electromagnetism for the first time.

Cont… • In 1905, the theoretical implications of electromagnetism led to Albert Einstein's theory of special relativity.

Electromagnet • When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.

Cont… • We can make an electromagnet stronger by doing these things: • wrapping the coil around an iron core • adding more turns to the coil • increasing the current flowing through the coil.

Electromagnetism: Definition • The word Electromagnetism is a compound form of two Greek terms, ἢλεκτρον, ēlektron, "amber", and μαγνήτης, magnētēs, "magnet". • It is a branch of physical science that deals with the physical relations between electricity and magnetism.

Circuit Theory Introduction to Electromagnetic Fields Maxwell’s equations Fundamental laws of classical electromagnetics Geometric Optics Electro-statics Magneto-statics Electro-magnetic waves Special cases Statics: Transmission Line Theory Input from other disciplines Kirchoff’s Laws

Introduction to Electromagnetic Fields • Maxwell’s Equation • Maxwell's equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electrodynamics (classical electromagnetism), classical optics, and electric circuits. • Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents. • Classical Electromagnetism is a branch of theoretical physics that studies consequences of the electromagnetic forces between electric chargesand currents.

Introduction to Electromagnetic Fields • Electromagnetics is the study of the effect of charges at rest and charges in motion. • Some special cases of electromagnetics: • Electrostatics: charges at rest (Static Electricity) • Magnetostatics: charges in steady motion • Electromagnetic waves: waves excited by charges in time-varying motion.

Introduction to Electromagnetic Fields • transmitter and receiver • are connected by a “field.”

Cont… • When an event in one place has an effect on something at a different location, we talk about the events as being connected by a “field”. • A fieldis a spatial distribution of a quantity; in general, it can be either scalar or vector in nature.

Cont… • Electric and magnetic fields: • Are vector fields with three spatial components. • Vary as a function of position in 3D space as well as time. • Are governed by partial differential equations derived from Maxwell’s equations.

Introduction to Electromagnetic Fields • Fundamental vector field quantities in electromagnetics: • Electric field intensity • Electric flux density (electric displacement) • Magnetic field intensity • Magnetic flux density units = volts per meter (V/m = kg m/A/s3) units = coulombs per square meter (C/m2 = A s /m2) units = amps per meter (A/m) units = teslas = webers per square meter (T = Wb/ m2 = kg/A/s3)

Introduction to Electromagnetic Fields • Universal constants in electromagnetics: • Velocity of an electromagnetic wave (e.g., light) in free space (perfect vacuum) • Permeability of free space • Permittivity of free space: • Intrinsic impedance of free space: 19

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Electromagnetism