ELECTROMAGNETISM

By:Joshua Alfred De la CruzNicole Marie Dela CruzStephen Miayo

History

The origin of electricity is and magnetism sprang from ancient men’s curiosity over the ability of two materials, amber and lodestone to attract other materials.

With the publication of James Clerk Maxwell's 1873 Treatise on Electricity and Magnetism in which the interactions of positive and negative charges were shown to be regulated by one force.

History

There are four main effects resulting from these interactions, all of which have been clearly demonstrated by experiments:

Electric charges attract or repel one another with a force inversely proportional to the square of the distance between them: unlike charges attract, like ones repel.

History

Magnetic poles attract or repel one another in a similar way and always come in pairs: every north pole is yoked to a south pole.

An electric current in a wire creates a circular magnetic field around the wire, its direction depending on that of the current.

History

A current is induced in a loop of wire when it is moved towards or away from a magnetic field, or a magnet is moved towards or away from it, the direction of current depending on that of the movement.

Magnetism

It is the term used to refer to the ability of lodestones to attract iron.

A material having this property is called a magnet.

The modern name for lodestone or magnetic iron ore is magnetite.

Classification

Natural◦ They are found in nature and are called lodestones or magnetite.

Artificial◦ May be temporary or permanent.◦ Retentivity is the ability of a magnetic material to retain its magnetism after it has been magnetized.

Classification

Electromagnet

◦A magnet whose magnetic field is produced by electric current passing through coils of wire wrapped around a core.

Types

Ferromagnetism

◦ Are strongly attracted be a magnet.

◦ They include iron, cobalt, nickel, and steel.

◦ In ferromagnetic materials, all electrons are spinning in the same direction.

Diamagnetism

◦ Is a weak response to magnetic field.

◦ Materials are repelled by a magnetic field.

◦ Metals, like bismuth, copper, gold, silver, lead, nonmetals, water, and organic compounds are diamagnetic.

Types

Paramagnetism

◦Weakly attracted to magnets.

◦When cooled, more magnetic.

Geomagnetism

Referred as Earth’s magnetism.

William Gilbert- conducted experiments and concluded that the Earth was a huge magnet.

Law of Magnetic Poles

Peter Petegrinus- same poles repel.

William Gilbert- confirmed it.

John Michael- force of attraction or repulsion between poles varies inversely as the square of the distance between them.

Law of Magnetic Poles

Charles de Coulomb- force between two poles is directly proportional to the product of the poles and inversely proportional to the square of the distance between them.

By combining these relation, he proposed the equation:

m1m2

F= kd2

Where F is the force, k as the constant, m are pole strengths in ampere, and d is the distance in meters.

Magnetic Field

Is a region of space where a magnet is capable of exerting a force on a magnetic material.

Analogous to the electric field around an electric charge.

Magnetic Field

Is also defined in terms of the force exerted on an electric charge moving in the field.

Michael Faraday- introduced the idea that the magnetic field is made up of lines of force which is called the magnetic flux.

Magnetic Field

Magnetic flux- it’s unit is weber(Wb), flux per unit area perpedicular to te fiel is called magnetic field intensity– the SI unit for I is tesla. Named afte Nikola tesla.

Magnetic Effect of Current

Chistian Oersted- made a demonstration on the heating effect of a current.

◦ by this , he accidentally discovered that a current-carrying conductor produces a magnetic field and this was influenced the orientation of the nearby compass.

◦ right hand rule- the magnetic field produced by a current may be determined by this.

The Electromagnet

A magnet whose magnetic field is produced by electric current passing through coils of wire wrapped around a core and the strength depends on the number of turns and current.

The first ever electromagnet was made by William Sturgeon and later improved by Joseph Henry.

Uses

They can be turn on/off.

The strength can be varied.

Very large magnetic field can be produced.

Used in steel yards.

Essential parts in the construction of electric meters, electric generators, circuit breakers, motors and others.

Electromagnetic Induction

Process by which a changing magnetic flux produces electric current.

The current and emf produce is called induced current an induces emf.

There are two laws describing the electromagnet induction: Faraday’s law and Lenz’s law.

Electromagnetic Induction

Faraday’s law- states that whenever there is a change in the magnetic flux in a circuit, an induced current is produce.

Lenz’s law- states that the induced current flows in a direction so as to oppose the change causing it.

Application

Discovery of Faraday and Henry paved the development of the generator, transformer and other devices that made the production of electricity cheaper.

AC/DC Generator

Converts mechanical energy to electrical energy.

Hyppolyte Pixii- was credited for having made the first electric generator.

Parts of a Simple AC generator

armature- consist of coils of insulated wire wound around a soft iron core.

- attached to a shaft so that it can rotate between the poles of the magnet.

- ends are connected to the external circuit by means of slip rings that rotate with the armature.

Parts of a Simple AC generator

Slip rings- made of either brass or copper.

- insulated from each other and from he shaft.

- each rings slides against the stationary brush .

Brush- collect the current and transmit it to the external circuit.

Motor

A generator operating reverse.

Changes electrical energy to mechanical energy.

Has the same parts as a simple DC generator.

Parts of a Motor

Brushes are connected to a battery to send current to the armature.

Magnetic field produced by this current in the armature interacts with the field of the magnet and exerts a force that rotates the armature.

A shaft attached to the armature makes the motion for doing work.

Parts of a Motor

Transformer

a device used to raise or lower the voltage of an AC source.

consist primary and secondary coils placed side by side having a common iron core.

Transformer

Plays a major role in power transmission.

Whenever electricity is transmitted , there is always loss of power because of the resistance of the transmission wires.

Types of Transformer

Step down transformer- lowers the voltage.

Step up transformer- raises the voltage.

THE END…

THANK YOU!