Can You Answer Master and Journeyman Exam Electrical Theory Related Questions With Ease?

Making sure that you can effectively answer electrical exam theory related questions is the key to successfully preparing to pass your electrical exam.

Question: 

What is the true power of an 120 volt single-phase AC circuit it the circuit current is 20 amperes and the voltage and amperage have a phase angle of 45 degrees?

Solution:

True power represents the power used by a system to do useful work and is traditionally expressed in the unit of watts.

The reference to a phase angle of 45 degrees is an indication that the voltage and current are out of phase.

Step #1 

Use ohm’s law to convert the voltage and amperage to volt-amps

VA = E x I

= 120 volts x 20 amps

= 2,400 volt-amps

Step #2 

Find the cosine of the phase angle by entering 45, then pressing the cosine function on a scientific calculator.

The cosine of 45 degrees = 0.67 or a power factor or 67%

Multiply the volt-amps from Step #1 by the cosine of 45 degrees

= 2,400 volt-amps x .67

= 1,608 volt-amps final answer

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