Prev. 100Electric Insolation1 Electric Mains1 Electric Mass1 Electric Matter1 Electric Mortar1 Electric Motor1Electric Organ1 Electric Oscillation1 Electric Oscillations1 Electric Osmose1 Electric Pen1 Electric Pendulum1 Electric Piano1 Electric Picture1 Electric Pistol1 Electric Potential Difference1 Electric Power1 Electric Pressure1 Electric Probe1 Electric Prostration1 Electric Protector1 Electric Quantity1 Electric Radiometer1 Electric Ray1 Electric Reduction of Ores1 Electric Register1 Electric Residue1 Electric Resonance1 Electric Resonator1 Electric Saw1 Electric Screen1 Electric Shock1 Electric Shower Bath1 Electric Soldering1 Electric Spark1 Electric Sphygmograph1 Electric Storms1 Electric Striae1 Electric Subway1 Electric Sunstroke1 Electric Superficial Density1 Electric Swaging1 Electric Tanning1 Electric Target1 Electric Tele-barometer1 Electric Telemeter1 Electric Tempering1 Electric Tension1 Electric Thermometer1 Electric Thermostat1 Electric Torpedo1 Electric Tower1 Electric Transmission of Energy1 Electric Trumpet1 Electric Tube1 Electric Typewriter1 Electric Varnish1 Electric Welding1 Electric Whirl1 Electric Wind1 Electrical Aura1 Electrical Cements1 Electrical Classification of Elemen...1 Electrical Convection of Heat1 Electrical Death1 Electrical Efficiency1 Electrical hazard2 Electrical Rectification of Alcohol1 Electrical Reduction of Phosphorous1 Electrically Controlled Valve1 Electricity5 Electrics1 Electrification1 Electrification by Cleavage1 Electrification by Pressure1 Electrization1 Electro Diagnosis1 Electro- Gilding1 Electro- Plating1 Electro-biology1 Electro-capillarity1 Electrochemical cell1 Electro-chemical Equivalent1 Electro-chemical Equivalents1 Electro-chemical Series1 Electro–chemistry1 Electro-culture1 Electrode1 Electro-diagnosis1 Electro-dynamic Attraction andRepul...1 Electro-dynamic Rotation of Liquids1 Electro-dynamic. adj.1 Electro-dynamics1 Electrolier1 Electrolysis1 Electrolyte1 Electrolytic Analysis1 Electrolytic Cell1 Electrolytic Clock1 Electrolytic Conduction1 Prev. 100

Electric Motor

A machine or apparatus for converting electric energy into mechanical kinetic energy. The electric energy is generally of the dynamic or current type, that is to say, of comparatively low potential and continuous or virtually continuous flow. Some electrostatic motors have, however, been made, and an influence machine can often be operated as a static motor.

Electric motors of the current type may be divided into two classes--direct current and alternating current motors.

Direct current motors are generally based on the same lines of construction as dynamos. One of the great discoveries in modern electricity was that if a current is passed through a dynamo, the armature will rotate. This fact constitutes the principle of the reversibility of the dynamo.

Motors built on the dynamo model may be series wound, shunt wound, or compound wound, or of the magneto type, in the latter case having a fixed field irrespective of any current sent through them. The field may be produced by an electro-magnet separately excited and unaffected by the current sent through the motor.

A current passed through a magneto or motor with separately excited field will turn it in the direction opposite to that required to produce the same current from it were it worked as a generator.

A current passed through a series wound motor acts exactly as above.

Both these facts follow from Lenz's law, q. v.

A current passed through a shunt wound motor acts oppositely to the above. The direction of rotation is the same as that required to produce a current of the same direction. This is because the field being in parallel with the armature the motor current goes through the magnet coils in the direction the reverse of that of the current produced in the armature when it is used as a dynamo. Hence this also carries out Lenz's law.

The compound wound motor acts one way or the other according as its shunt or series winding preponderates. The two may exactly balance each other, when there will be no motion at all. The series connections of a compound wound dynamo should therefore be reversed, making both series and shunt work in unison, if the dynamo is to be used as a motor.

The general principles of the electric motor of the dynamo, or continuous rotation type, can only be outlined here. The current passing through the field magnets polarizes them and creates a field. Entering the armature by the brushes and commutators it polarizes its core, but in such a way that the north pole is away from the south pole of the field magnet, and the same for the south pole. Hence the armature rotates. As it does this the brushes connect with other commutator sections, and the poles of the armature are shifted back. This action continues indefinitely.

Another class of motors is of the reciprocating type. These are now very little used. (See Reciprocating Motor)

One valuable feature of continuous rotation electric motors is the fact that they absorb energy, to a great extent proportional in amount to the work they have to do. The rotation of the armature in the field of the motor involves the cutting of lines of force by its coils. This generates an electro-motive force contrary in direction to that producing the actuating current. The more rapid the rotation the greater is this counter-electro-motive force. The motor armature naturally revolves faster with diminished resistance to the motion of the armature. This increases the counter-electromotive force, so that less energy is absorbed. When the motor is called on to do work, the armature rotates more slowly, and the counter-electro-motive force diminishes, so that the machine absorbs more energy. (See Jacobi's Law)