Current Creates Magnetism

Current Creates MagnetismWhenever a current flows through a wire, magnetic lines of force are created around the wire. These lines of force are small concentric circles formed around the wire. These circular lines of magnetic force have no polarity.

Current Creates Magnetism

Current Creates MagnetismThe magnetic lines leave the inside of the loop at the north pole, flow around the outside of the loop, and re-enter at the south pole � just like a bar magnet.

Right-Hand Rule, Straight WireThe direction of current flow can be determined by applying the right-Hand Rule.

Right-Hand Rule, Straight WireGrasp a straight conductor with your right hand with your fingers on the leading side of the conductor, with your right hand with your fingers on the leading side of the conductor, and pointed in the direction of the magnetic lines of force. Your thumb will then point in the direction of current flow.

ElectromagnetismWhen a wire carrying electric current is wound into a coil, a magnetic field with north and south poles is created, just as in a bar magnet. If an iron core is placed inside the coil, the magnetic field becomes much stronger because iron conducts magnetic lines more easily than air.

Electromagnetism

ElectromagnetismAn iron core can increase the strength of the magnetic field by as much as 2500 times This arrangement, called an electromagnet, is used in alternators to create strong magnetic fields by winding many turns of current-carrying wire around iron core called pole pieces.

Electromagnetic FactsThe number of magnetic lines of force is proportional to the number of ampere turns of the coil. The number of magnetic lines of force is inversely proportional to the field reluctance.

Electromagnetic FactsHigh reluctance = fewer lines of force. Lower reluctance = more lines of force.

Electromagnetic InductionWhen a magnetic field is moved so its lines of force cut across a wire or conductor. When a voltage is generated by magnetic lines of force cutting across a conductor, the process is called electromagnetic induction.

Electromagnetic Induction

Electromagnetic InductionIn an alternator, the field moves, and the conductor is stationary. In a generator, the conductor moves, and the field is stationary. In an alternator, a magnet is rotated inside the stationary conductor so lines of force cut across the conductor.

Electromagnetic InductionVoltage is induced in the stationary conductor, called a stator. The rotating magnet is called the rotor.

Right � Hand Rule for CoilsWith lines of force leaving the coil at one end and entering at the other, a north and south pole are formed at the coil ends, the same as in a bar magnet. To find polarity of the coil ends, apply the Right-Hand Rule for coils. If the current direction through the coil is reversed, the polarity of the coil ends will also reverse.

Relay Operation

Relay OperationA relay, which is actually a switch, provides a way to control a large amount of current with a small amount. Typically, a relay has both a control circuit and a power circuit. The control circuit is fed current by the power source.

Relay OperationThe current flows through a switch and an electromagnetic coil to ground. The power circuit is likewise fed current from the power source, and the current flows to an armature, which can be attracted by the magnetic force on the coil.

Relay OperationWhen the control circuit switch is open, no current flows to the relay and the coil is not energized. The contacts are open and no power goes to the loads.

Relay OperationWhen the control circuit switch is closed, however, current flows to the relay and energizes the coil.

Relay OperationThe resulting magnetic field allows power to the load by pulling the armature down and closing the contacts.

Solenoid Operation

Solenoid Operation

Solenoid OperationSolenoids are electromagnetic switches. The solenoid�s movable core converts current flow into mechanical movement. In a pulling-type solenoid, the magnetic field pulls the core into the coil or holds the core in place. These solenoids are called magnetic switches.

Solenoid OperationIn a push-pull-type solenoid, the core is a permanent magnet. The core is pulled in or pushed out when current flow direction is changed. Solenoids are now being used in automatic transmissions to control shifting. They eliminate the need for a TV cable and governor.