chapters 29, 30 DC machines, DC Motor

counter torgue

a measure of the useful electric energy produced by the generator.

The _____ ride against the commutator segments and are used to connect the armature to the external circuit of the DC machine.

brushes

the brushes ride against the commutator segments and are used to connect the armature to the external circuit of the DC machine.

brushes

The motor that does not contain a wound armature, commutator, or brushes is the

brushless DC motor

What is the component of a DC generator that converts the armature AC into DC?

commutator

What is the component of a DC generator that converts the armature AC into DC? ​

commutator

A coil has an inductance of 3 H and a wire resistance of 15 f2. How long will it take for the current to reach its full value?

1.0 seconds

A square wave voltage varies between 0 V and 12 V. The positive pulses are 50 jus wide and there is a 50 jus gap between them. What is the DC average of the waveform?

6 V

a square wave voltage varies between 0 V and 12 V. The positive pulses are 75 us wide and there is a 25 us gap between them. What is the DC average of the waveform?

9 V

What is a device that converts mechanical energy into DC electrical energy?

a generator

Counter-electromotive force (CEMF) and back-EMF are names for the voltage induced into the armature of a DC

true

The amount of voltage induced into a conductor depends on the turns of wire, the strength of the magnetic field, and the speed of cutting action.

true

When the current flow through an inductor stops and the current also decreases at an exponential rate, a volt spike occurs.

volt spike

Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. Which type of winding provides high voltage and low current?

wave-wound

Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. Which type of winding provides high voltage and low current?

wave-wound

When a closed loop of wire cuts through magnetic flux lines, a current is induced into the loop. The current in the loop sets up a magnetic field that is in opposition to the original magnetic flux. This is essentially ______ ​

Lenz's law

The output voltage of a generator is usually controlled by the amount of

Field excitation current

The direction of induced current can be determined by using fleming left-hand generator rule.

Fleming

When a DC machine is used as a generator, the commutator performs the function of a mechanical rectifier to change the AC produced in the armature into DC before it exits the machine through the brushes.

commutator

The relationship of the strengths of the two fields in a generator determines the amount of

compounding

A compound generator has both series and shunt field windings. When those windings are connected so they aid cach other in the production of magnetism, that connection is called

cumulative-compound

When using the left-hand generator nale, the center finger points to the direction of

current

The compound motor connection that should generally be avoided is the

differential

Losses in the core of iron core inductors include eddy current and hysteresis losses.

eddy current; hysteresis

When a conductor cuts magnetic lines force, a voltage is induced into the conductor. This principle is called

electromagnetic induction

Series field windings are connected in series with the armature. They are wound with few turns of fairly large wire

few; large

Exponential curves are always divided into 5 time constants.

five

What is a device that converts mechanical energy into DC electrical energy?

generator

A device that converts electrical energy into mechanical energy is called a(n)

motor

If a conductor is moved upward, the polarity of induced voltage is reversed and the current flows in the opposite direction.

opposite

The ServoDisc motor is also often called a

printed-circuit motor

If a voltage is being induced into a conductor by electromagnetic induction, reversing the direction of motion of the conductor will

reverse the polarity of the induced voltage

new

section

The series generator has only a series field, which is connected in series with the armature.

series

Small permanent magnet motors that have lightweight rotors are often used as

servomotors

A compound motor has shunt field windings.

shunt

The DC motor, known as a "constant speed motor," is the shunt motor.

shunt