Electromagnetism

1. Electromagnetism

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

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

9. 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.

10. 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.

11. 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.

12. 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

13. 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.

14. 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.

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

16. 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.

17. 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.

18. 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)

19. 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

20. Any Questions…????