1 DC ELECTRICAL CIRCUITS MAGNETISM. 2 DC ELECTRICAL CIRCUITS A magnet is a material or object that...

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DC ELECTRICAL CIRCUITS

MAGNETISM

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A magnet is a material or object that produces a magnetic field, the first known magnets were called magnetites or lodestones.

This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.

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A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field.

An everyday example is a refrigerator magnet used to hold notes on a refrigerator door.

Temporary magnets quickly lose their magnetism.

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Magnets are classified by the materials they’re made of like metallic or ceramic.

They’re further classified by the alloys they’re made from.

Magnets are labeled North (N) and South (S) because they align themselves with the earth’s magnetic poles.

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The magnetic fields form lines around a magnet and are called flux lines that follow four rules;

1. They have direction or polarity2. They always form complete loops3. The flux lines can not cross each

other.4. They form the smallest possible

loops.

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When current flows through a wire a magnetic field is developed around the wire, the direction of the field depends on the direction of current flow.

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The direction of the flux lines can be determined if the direction of the current flow is known, to do this we use the left hand rule.

You grab the conductor with your left hand using your thumb to point in the direction of current flow, your finger point in the direction of the magnetic flux lines.

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An electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops.

Often, the coil is wrapped around a core of "soft" ferromagnetic material such as steel, which greatly enhances the magnetic field produced by the coil.

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An electromagnet, in its simplest form, is a wire that has been coiled into one or more loops, known as a solenoid.

Types of electromagnets

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The left hand rule for coils helps you determine the north pole of magnetic coil, you wrap your hand around the coil in the direction of current flow (fingers point toward current flow) and your thumb will point to the North pole.

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Electromagnetic induction is the action that causes electrons to flow in a conductor when the conductor moves across a magnetic field.

IF THIS CONDUCTOR IS CONTINUOUSLY MOVED UP AND DOWN THROUGH THE MAGNETIC FIELD ELECTRONS WILL CONTINUE TO FLOW CREATING INDUCED EMF.

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The amount of EMF induced in a conductor is determined by four factors:

1. The strength of the magnetic field.2. The speed of the conductor through the

field.3. The angel at which the conductor cuts

the field.4. The length of the conductor in the field

(in terms of coils).

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These four factors are the basis for Faraday’ law.

Faraday’s law states;The voltage induced in the conductor

is directly proportional to the rate at which the conductor cuts the magnetic lines of force.

In other words, the more flux lines cut per second, the higher the induced EMF.

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The Faraday flashlight uses a capacitor charged up by moving a magnet back and forth through a coil instead of batteries, output of coil is fed to a capacitor through a full wave rectifier so it charges up with the magnet going right to left and vice versa.

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The polarity of the induced EMF can be determined by the left hand rule for generators

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The majority of voltage produced in the world today (approx. 95%) is produced by the use of magnetic induction.

A BASIC ELECTRIC GENERATOR.

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The AC (alternating current) generator converts mechanical energy into electrical energy through electromagnetic induction.

An armature made up of laminated copper coils spins through a magnetic field.

Using water pressure (as in hydro electric) to spin the armature causes EMF to be produced.

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As the coil (armature) cuts through the magnetic field it creates the maximum positive voltage at 90 degrees and the maximum negative voltage at 270 degrees.

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The DC (direct current) generator is similar to an AC generator but it has a commutator that converts the AC to pulsating DC.

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