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it 137 midterm 3
| Question | Answer |
|---|---|
| magnetic flux | invisible lines in a magnet that travel north to south on the interior and south to north on the exterior |
| Magnetic permeability | A material's ability to absorb magnetic flux |
| What type of materials have high permeability? | Ferromagnetic |
| Reluctance | Opposition to the passage of magnetic lines of force. |
| What three elements are magnetic lines not able to pass through. | Nickel, Cobalt, iron |
| Retentivity | Ability to retain magnetic field after removal of magnetic force |
| How to create a magnetic field around a conductor? | Pass an electrical current through it |
| Relay | a small device that connects a small voltage/current to a large voltage/current |
| solenoid effect | uses a coil wire to try to center a sliding ferromagnetic core |
| ampere turns | amperes x the number of turns in the coil of the electromagnet |
| electromagnet | A coil wrapped around a soft iron core. When current runs through the coil the core becomes magnetized |
| flux density | Number of lines of flux per cross-sectional area of magnetic circuit |
| hysteresis | A property that causes magnetization to lag behind the force that produced it |
| magnetic shielding | conducting magnetic lines around an object |
| residual magnentism | magnetism remaining in a material after the magnetizing force is removed |
| alternator versus generator | one uses a magnetic field the other doesn't? |
| amplitude | maximum range of a quality |
| armature | revolving part in a generator or motor. |
| average value | 1/area |
| brushes | Sliding contact between commutator external circuit in a dc generator |
| commutator | Mechanical switch to maintain current in one direction in an external circuit |
| cycle | one complete segment of alternating current from positive to negative and back to the starting point |
| eddy current | induced current flowing through the core of an electromagnetic device |
| Len'z Law | Induced emf is always in such a direction that it opposes the effect that produces it |
| Magnetic induction | moving a conductor through a magnetic field to induce voltage |
| peak | maximum value of a sine wave |
| peak-to-peak | Measure of the peak in a positive direction to the peak of a negative direction |
| period | time for one complete cycle |
| phase displacement | equal to the angle between the two polar vectors when current and voltage waves are out of phase |
| rectification | changing from alternating current to direct current. |
| rotor | rotating part of an ac generator |
| sine wave | depicts the flow of alternating current |
| slip wrings | metal rings connected to armature windings to connect an external circuit |
| stator | stationary coils of an ac generator |
| counterelectromotive force | voltage induced in a conductor moving through a magnetic field that opposed source voltage |
| field windings | electromagnets that can replace permanent field magnets in a generator motor to make it more powerful |
| locked rotor | a rotor that is not turning while power is being applied to the motor because of physical impedance |
| servo motor | any motor that is modified to give feedback concerning the motors speed, direction of rotation, and number of revolution |
| stepper motor | a motor designed to rotate in small increments, using a series of digital pulses to control rotation |
| torque | turning power of a motor |
| voltage ratio | the ratio between the voltages of the primary and secondary windings |
| turns ratio | the number of turns the primary winding of the transformer compared to the number of turns of the secondary winding |
| step up transformers | used to raise a voltage |
| step down transformers | used to lower a voltage |
| self inductance | induced in a current carrying conductor |
| mutual induction | two coils located so that the magnetic flux of one coil can link with the turns of another coil. The change in flux in one causes an emf in the other |
| laminations | thin sheets of steel used in the cores of transformers, generators and motors. |
| isolation transformers | a transformer that isolates the primary circuit from the secondary one |
| impedence | the resistance to flow of ac current |
| hysterisis loss | energy loss due to molecular friction occurs as molecules move through the cycle of magnetization |
| eddy current loss | as energy flows through the core heat is lost due to the resistance of the core |
| current ratio | ration betwwen primary and secondary windings in a transformer |
| coupling | percentage of mutual inductance between coils |
| copper losses | Resistance of wire causes heat loss in motors transformers and generators |
| autotransformers | has a common primary and secondary winding. Taps on common winding cause step-up/down |
| slip | the difference in rotor speed and the magnetic field of the stator in in ac motors |
| squirrel cage rotor | made of bars placed in slots of the rotor core and joined at the ends. |
| synchronous speed | rotor speed equals the speed of the rotating magnetic field |
| motor effect | two magnetic fields cannot occupy the same space at the same time so. If their poles attract n-s, n-s then they will combine if they oppose, N-N, s-s, then th more powerful one will expel the other |
Created by:
camcox3