# Study Test Questions D1 Flashcards

If the peak to peak voltage is 588.4 and the heating load is 2000watts of heat what is the resistance of this heat?

Peak to peak voltage / 2 =

peak voltage x 0.707 = E (RMS)

R= E*2/P

588.4/2= 294.2Em x 0.707= 208E

208*2\2000=21.632 ohms

If a source has an instantaneous voltage of 50 at 18• degrees, what would the instantaneous voltage be at 80degrees?

Instant to peak voltage

50E x sine 18• = 161.8Em

First angles max voltage to another angle at max voltage.

161.8Em x 80• = 159.34Em

State three reasons why alternating current is used more than direct current?

Cheaper, smaller, simpler, the step up or step down fiction of a transformer

List five applications where direct current is preferred or required instead of alternating current.

Mining, high intensity light sources that use carbon arcs, electro-plating, battery charging, precise speed, synchronized motors and alternators

What does Epp stand for?

Peak to peak value

2 X the peak

What is another name for RMS OR ROOT MEAN SQUARE?

Effective Value

At what angle in a sine wave does peak value occur?

90° and -270°

With respects to the peak value, what is the average value of an AC sine wave?

0°

With respects to the peak value, what is the average value of one alternation of an AC Sine wave?

.637

What two meters must be use to determine the effective resistance of an AC circuit?

Watt meter and amp meter

Ohm and volt meters might explode

What term is used to refer to the circulating currents in a magnetic core?

Eddy currents

As the frequency of the AC Increases, the effective resistance_____________.

Increases

What are the three formulas for finding Frequency, voltage and number of field poles?

F= PxN/120

N= 120xF/P

P= 120xF/N

P= poles N= speed in rpm F= Frequency

The peak power in an AC lighting circuit is 1200w. What is the effective power in that circuit?

P= 0.5 x Pm

= 0.5x1200w

=600w

What is the instantaneous voltage at 30° into the AC cycle on a sine wave with an effective value of 480E?

E= 0.707x Em

Em= E/0.707

= 480/0.707x VOLTAGE

=679 Em

e = sine 30°x 679V

=0.5x 679v

= 339.5e

If an AC source with a peak voltage of 339.4 Em is placed across a load with a resistance of 288ohms, what power will the resistance dissipate?

E= 0.707 x Em

P= E*2/R

200w

What is the frequency of an alternating voltage produced by a 10-pole alternator turning at a speed of 600rpm?

F= PxN/120

50hz

An turns at a speed of 450 rpm and produces an alternating current of 60 Hz. How many poles does this alternator contain?

P= fx120/ N

16 poles

At what rpm must a prime mover turn a six pole alternator to produce an alternating voltage with a frequency of 50Hz?

N= 120xF/P

1000rpm

What is the effective voltage of a sine wave with a peak value of 679 volts?

E = Em x 0.707

480.053 E