The Tesla (T) and the Gauss (G) are both units for magnetic flux destiny.
The Unit for measuring magnet-motive force (mmf) is the volt.
Ohm's law for a magnetic circuit gives the relationship between flux destiny, magnet-motive force, and reluctance.
A Solenoid is a form of electromagnetic switch that opens and closes mechanical contacts.
A hysteresis curve is a plot of flux density (B) as a function of field intensity (H).
To produce an induced voltage in a coil, the magnetic field surrounding can be changed.
The speed of a generator can be controlled with a rheostat in the field winding's.
A self-excited dc generator will normally have enough residual magnetism in the the field magnets to start the generator producing voltage at the output when it is first turned on.
The power developed by a motor is proportional to its torque.
In a brushless motor, the magnetic field is supplied by permanent magnets.
The period of a 60 Hz sine is 16.7 ms.
The rms and average value of a sine wave are the same.
A sine wave with a peak value of 10 V has the same heating effect as a 10 V dc source.
The peak value of a sine wave is the same as its amplitude.
The number of radians in 360 degrees is 2π.
In a three-phase electrical system, the phases are separated by 60°
The purpose of an exciter is to supply dc rotor current to an alternator.
In an automotive alternator, the output current is taken from the rotor through slip rings.
A maintenance issue with induction motors is brush replacement.
A synchronous motor can be used when constant speed is required.
When the south poles of two bar magnets are brought close together, there will be
a force of attraction
a force of repulsion
an upward force
no force
A magnetic field is made up of
positive and negative charges
magnetic domains
flux lines
magnetic poles
the Direction of a magnetic field is from
north pole to south pole
south pole to north pole
inside to outside the magnet
front to back
Reluctance in a magnetic circuit is analogous to
voltage in an electric circuit
current in an electric circuit
power in a electric circuit
resistance in a electric circuit
The unit of magnetic flux is
tesla
weber
ampere-turn
ampere-turns/weber
The unit of magneto-motive force is the
ampere-turns/ weber
The unit of flux density is the
electron-volt
The electromagnetic activation of a movable shaft is the basis for
relays
circuit breakers
magnetic switches
solenoids
When there is current through a wire placed in a magnetic field,
the wire will overheat
the wire will become magnetized
a force is exerted on the wire
the magnetic field will be cancelled
A coil of wire is placed on a changing magnetic field. if the number of turns ion the coil is increased, the voltage induced across the coil will
remain unchanged
decrease
increase
be excessive
if a conductor is moved back and forth at a constant rate in a constant magnetic field, the voltage induced in the conductor will
remain constant
reverse polarity
be reduced
be increased
In the crankshaft position sensor in figure 10-33, the induced voltage across the coil is caused by
a current in the coil
rotation of the steel disk
a tab passing through the magnetic field
acceleration of the steel disks rotational speed
The purpose of the commutator in a generator or motor is to
change the direction of the current to the rotor as it spins
change the direction of the current to the stator winding's
support the motor or generator shaft
provide the magnetic field for the motor or generator
In a motor, back emf serves to
increase power from the motor
decrease flux
increase the current in the field windings
decrease the current in the armature
The torque of a motor is proportional to the
amount of flux
armature current
both of the above
none of the above
The difference between alternating current (AC) and direct current (DC) is
ac changes value and dc does not
ac changes direction and dc does not
both answers A and B
neither answers A and B
During each cycle, a sine wave reaches a peak value
one time
two times
four times
a number of times depending on the frequency
A sine wave with a frequency of 12 kHz is changing at a faster rate than a sine wave with a frequency of
20 kHz
15,000 Hz
10,000 Hz
1.25 MHz
A sine wave with a period of 2 ms is changing at a faster rate than a sine wave with a period of
1 ms
0.0025 s
1.5 ms
1200 ms
when a sine wave has a frequency of 60 Hz, in 10 s it goes through
6 cycles
10 cycles
1/16 cycle
600 cycles
if the peak value of a sine wave is 10 V, the peak-to-peak value is
20 V
5V
100V
none of these
I the peak value of a sine wave is 20V, the rms value is
14.14 V
6.37 V
7.07 V
5 V
The average value of a 10 V peak sine wave over one complete cycle is
0 V
The average half-cycle value of a sine wave with a 20 V peak is
12.74 V
One sine wave has positive-going zero crossing at 10° and another sine wave has a postive going zero crossing at 45°. The phase angle between the two wave-forms is
55°
35°
0°
The instantaneous value of a 15 A peak sine wave point at a 32° from its postive-going zero crossing is
7.95 A
7.5 A
2.13 A
7.95 V
A phasor represents
thew magnitude of a quantity
the magnitude and direction of a quantity
the phase angle
the length quantity
if the rms current through a 10kΩ resistor is 5 mA, the rms voltage drop across the resistors is
70.7 V
50V
Two series resistors are connected to an AC source, If there are 6.5 V rms across one resistor and 3.2 V rms across the other, the peak source voltage is
9.7 V
9.19 V
13.72 V
4.53 V
An advatage of a three-phase induction motor is that it
maintains constant speed at any load
does not require starting winding's
has a wound rotor
all of the above
The difference in the synchronous speed of the stator field and the rotor speed of the motor is called
differential speed
loading
lag
slip
a 10kHz pulse waveform consists of pulses that are 10us wide. Its duty cycle is
100%
10%
1%
not determinable
The duty cycle of a square wave
varies wit the frequency
varies with the pulse width
is 50%
