Completion
Complete each
statement.
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1.
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A permanent magnet has a ___________ field surrounding it.
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2.
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Amagnetic field is visualized by lines of _________ that radiate from the north
pole (N) to the south pole (S) and back to the north pole through magnetic material.
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3.
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When unlike poles of two permanent magnets are placed close together, their
magnetic fields produce an ___________ force.
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4.
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When two like poles are brought close together, the _________ each other.
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5.
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The fact that magnetic lines of _______ follow a path through iron or other
materials is a consideration in the design shields that prevent stray magnetic fields from affecting
sensitive circuits.
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6.
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The group of force lines going from the north pole to the south pole of a magnet
is called the magnetic ______, symbolized by j (phi).
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7.
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The unit of magnetic flux is the ____________.
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8.
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The magnetic flux density is the amount of flux per unit area perpendicular to
the _________ field.
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9.
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The unit for the magnetic flux density is the __________(T).
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10.
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Ferromagnetic materials such as iron, nickel, and cobalt become magnetized when
placed in the magnetic field of a _________.
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11.
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Ferromagnetic materials have minute magnetic domains created within their atomic
structure by orbital motion and spin of ___________.
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12.
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The hall effect is the occurance of a small voltage that is generated on
opposite sides of a thin current-carrying conductor or ______________ that is in a magnetic
field.
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13.
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Hall-effect sensors are used to measure various parameters such as throttle
angle, crankshaft and camshaft positions, distributor position, ____________, power seat and
rear-view mirror positions.
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14.
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Current produces a magnetic field, called an ______________ field, around a
conductor.
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15.
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Although the magnetic field cannot be seen, it is capable of producing
_____________ effects.
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16.
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An aid to remembering the direction of the lines of force is the ______ Hand
Rule.
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17.
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Imagine that you are grasping the conductor with your left hand, with your thumb
pointing in the direction of current. Your fingers indicate the direction of the ________ lines
of force.
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18.
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The ease with which a magnetic field can be established in a given material is
measure by the ______________ of the material.
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19.
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The opposition to the establishment of a magnetic field in a material is called
____________.
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20.
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The cause of a magnetic field is called the _______________ force.
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21.
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Like other phenomena in science, the flux is an effect, the mmf is a cause, and
the ___________ is an opposition.
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22.
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A basic ____________ is simply a coil of wire wound around a core material that
can be easily magnetized.
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23.
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A __________ is a type of electromagnetic device that has a movable iron core
called a plunger.
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24.
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As long as there is a coil current, the ________ remains retracted by the
attractive force of the magnetic fields.
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25.
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The solenoid is used for applications such as opening and closing _________ and
automobile door locks.
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26.
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Relays differ from solenoids in that the electromagnetic action is used to open
or close electrical _________ rather than to provide mechanical movement.
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27.
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Another widely used type of relay is the ________ relay.
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28.
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When there is a current through the coil, the reeds make contract because they
are ____________ and attract each other.
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29.
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Reed relays are faster, are more reliable, and produce less contact _________
than armature relays.
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30.
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________ relays have less current-handling capability than armature relays and
are more susceptible to mechanical shock.
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31.
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A speaker is an electromagnetic device that converts electrical signals into
__________.
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32.
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The audio signal is connected using very flexible wires to a cylindrical coil
called the _________ coil.
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33.
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Current from the audio input alternates back and forth and powers the
____________.
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34.
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The _______ is a flexible diaphragm that vibrates to produce sound.
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35.
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The d’Arsonval meter movement is the most common type used in _______
multimeters.
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36.
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A pointer is attached to the moving assembly. With no current through the
coil, a _________ mechanism keeps the pointer at its left-most (zero) position.
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37.
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When there is current through the coil, electromagnetic forces act on the coil,
causing a rotation to the right. The amount of rotation depends on the amount of
_________.
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38.
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A data bit (1 or 0) is written on the magnetic surface by the magnetization of a
small segment of the surface as it moves by the ________ head.
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39.
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A magnetized spot of one polarity represents a binary 1, and one of the opposite
polarity represents a ________ 0.
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40.
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Once a spot on the surface is magnetized, it remains until written over with an
___________ magnetic field.
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41.
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The magneto-optical disk uses an electromagnet and _______ beams to read and
write (record) data on a magnetic surface.
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42.
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A ________ senses the difference in the polarity of the reflected laser beam to
determine if the bit being read is a 1 or a 0.
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43.
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The magnetic field intensity in a material is defined to be the ______________
force per unit length of the material.
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44.
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_____________ us a characteristic of a magnetic material whereby a change in
magnetization lags the application of the magnetic field intensity.
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45.
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The ability of a material, once magnetized, to maintain a magnetized state
without magnetic field intensity is called __________.
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46.
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When a straight conductor is moved perpendicular to a magnetic field, there is a
relative motion between the conductor and the magnetic field. Likewise, when a magnetic field
is moved past a stationary conductor, there is also relative motion. In either case, this
relative motion results in an ____________ voltage.
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47.
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The amount of the induced voltage depends on the rate at which the conductor and
the magnetic field move with _________ to each other.
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48.
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Polarity of induced voltage depends on the __________ of motion of the conductor
relative to the magnetic field.
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49.
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The voltage induced across a coil equals the number of turns in the coil times
the rate of change of the __________ flux.
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50.
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When the current through a coil changes, the polarity of the induced voltage
created by the changing magnetic field is such that it always ________ the change in currrent that
caused it.
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51.
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_______ generators produce a voltage that is proportional to the magnetic flux
and the rotational speed of the armature.
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52.
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Motors convert electrical energy to __________ motion by taking advantage of the
force produced when a current-carrying conductor is in a magnetic field.
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53.
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The rotor in all dc motors contains the armature winding, which sets up a
_________ field.
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54.
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The _________ dc motor has the field coil windings and the armature coil
windings in series.
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55.
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A _________ dc motor has the field coil in parallel with the armature.
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56.
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The ________ wound motor will have a very high starting torque when the current
is high because flux and armature current are high.
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Matching
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Typical Flux Density in Teslas a. | 0.1 to 0.2 | e. | 0.2 to
0.3 | b. | 0.3 to 0.52 | f. | 1 | c. | 45 | g. | 0.08 to 0.1 | d. |  |
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57.
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Earth’s magnetic field
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58.
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Small “refrigerator” magnet
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59.
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Ceramic magnets
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60.
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Alnico 5 reed switch magnet
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61.
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Neodymium magnets
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62.
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Magnetic resonance imaging (MRI)
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63.
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The strongest steady magnetic field ever achieved in a laboratory
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a. | stator | d. | armature | b. | self-excited | e. | commutator | c. | brushes | f. | rotor |
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64.
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The conductive metal ring of a DC generator.
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65.
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The fixed contacts that commutators make contact with.
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66.
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A ferromagnetic core assembly connected to bearings and rotates in the magnetic
field.
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67.
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The stationary part of a generator (or motor) is known as the ________.
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68.
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The power producing component of a generator that can be on the rotor or the
stator.
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69.
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A method for using the generator itself to provide current for the
electromagnets.
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