# Kaplan- Lesson 6: Electical Systems Flashcards

1
Q

The three basic factors in electricity are…

A

potential, current, & resistance

2
Q

Potential electricity is measured in…

A

voltage (volts)- V

3
Q

Current electricity is measured in….

A

amperes (amps)- I

4
Q

Resistance electricity is measured in…

A

ohms (Ω)- R

5
Q

What is Ohm’s Law?

A

The formula that relates the three factors of electricity.

I = V / R

```I= current
V= voltage
R= resistance```
6
Q

What is direct current?

A

current that flows only in one direction with constant voltage.

7
Q

Equation for power in Direct Current (DC) circuit is….

A

P = V x I

```P= power
V= voltage
I= current```
8
Q

What is alternating current?

A

based on the concept that electricity has no inertia, and therefore the direction of the flow can be reversed very rapidly by reversing the voltage.

9
Q

Equation for power in a single-phase circuit is…

A

P = V x I x PF

```P= power
V= voltage
I= current
PF= power factor in decimal form```
10
Q

Equation for power in a three-phase circuit is…

A

Same as single-phase but multiply by the √3

P = V x I x PF x √3

```P= power
V= voltage
I= current
PF= power factor in decimal form```
11
Q

A wire wound spirally around an iron core to produce a magnetic field and that is used as an electromagnetic switch is called?

A

A solenoid

12
Q

The most basic form of power generation is…

A

a single-phase alternator

13
Q

What is the typical AC power frequency in the US and what is the most common household voltage?

A

60 hertz

110 volts

14
Q

Devices that change the voltage of an AC circuit to a higher or lower value are called ______.

A

Transformers

15
Q

How does a transformer work?

A

A transformer consists of an iron core on which two separate coils of wire are wound. The coil with the greater number of turns will have a higher voltage.

16
Q

A primary winding is the winding that is used for ____ in a transformer, while the secondary winding is used for ____.

A

Input; output

17
Q

Residences are limited to ____ volt single-phase systems.

A

120/240

18
Q

What are the four types of motors in general use?

A

DC Motor
Single-phase AC Motor
Three-phase induction Motor
Universal Motor

19
Q

What are DC motors used for?

A

Small scale applications and elevators

20
Q

What kind of motor is used in a mixer or hand drill?

A

Universal motor

21
Q

What are capacitors used for?

A

To improve the power factor in a circuit which improves efficiency and overall performance.

22
Q

In residential applications how far should receptacles (outlets) be placed?

A

No farther than 12 feet apart

23
Q

What is the maximum voltage drop due to resistances of the wire in a lighting circuit?

A

3 %

24
Q

What is the maximum voltage drop due to resistances of the wire in a circuit supporting motors?

A

5 %

25
Q

What are the three types of protection (shutoff devices) for a circuit?

A

Fuses
Circuit breakers
Ground fault interrupter (GFI or GFCI)

26
Q

A device that automatically disconnects a circuit when the current is excessive?

A

Circuit Breaker

27
Q

What is the device called that is composed of a soft metal link in a glass plug or fiber cartridge. If the link gets hot enough it will melt, breaking the circuit.

A

Fuse

28
Q

What device detects a continual current lost to ground, even after the power is shut off?

A

Ground Fault Interrupter (GFI or GFCI)

29
Q

To avoid excessive voltage drop and flicker, the distance from the transformer to the meter should not exceed ____ feet.

A

150’

30
Q

What are the two ways electric usage is measured?

A

Total consumption and Peak Demand

31
Q

The charge associated with peak demand in larger buildings is called a _________.

A

Demand surcharge.

32
Q

Given a 120 volt outlet and a hair dryer with a resistance of 8 ohms (Ω), the current flow through the hair dryer when it is turn on is ____ amps.

A. 15
B. 6.7
C. 1.5
D. 0.67

A

A. 15

```I = V/R
I = 120/8```
33
Q

If the power factor is 1 for the hairdryer in the previous question, the wattage rating is _____.

```V= 120
R= 8
I= 15```
A

1,800

```P = V x I x PF
P = 120 x 15 x 1```
34
Q

Given three parallel paths, two paths with a resistance of 4 ohms and one with a resistance of 2 ohms what is the total net resistance?

A. 0.125 ohms
B. 10 ohms
C. 1.25 ohms
D. 1. 0 ohms

A

D. 1.0 ohms

1 / [ (1/4) + (1/4) + (1/2) ]

1 / 1 = 1

35
Q

If the voltage between the neutral and the peak of a three-phase current is 120 volts, what is the voltage between two phases?

A. 120 volts
B. 208 volts
C. 240 volts
D. 277 volts

A

B. 208 volts

120 x √3

36
Q

A three-wire transformer means that

A. the primary winding is one of three input options.

B. the transformer generates three-phase current.

C. the secondary winding allows two different voltage takeoffs.

D. there is a tertiary winding.

A

C. the secondary winding allows two different voltage takeoffs.

37
Q

To provide five light switches for a large room, we need

I. two-way switches.
II. three-way switches.
III. four-way switches.

A. I & II
B. II & III
C. I & III
D. I, II, & III

A

B. II & III

II. three-way switches.
III. four-way switches.

38
Q

A variable speed mixer motor is most likely a

A. universal motor.
B. DC motor.
C. three-phase induction motor.
D. synchronous AC motor.

A

A. universal motor

39
Q

Which conduit system is unacceptable for embedding in concrete?

A. rigid conduit
B. flex conduit
C. IMC conduit
D. Armored cable

A

D. armored cable

40
Q

Which of the following is true about a ground fault interrupter?

I. It is a form of protection against short circuits.

II. It may be actuated even when there is no equipment switched on in the circuit.

III. It can completely disconnect a circuit.

A. I & II
B. II & III
C. I & III
D. I, II, & III

A

D. I, II, & III

41
Q

What is a demand surcharge?

A. a negative charge which builds up in a circuit when the current is too great.

B. The copper side of a capacitor.

C. A method by which utilities attempt to reduce the need for new power plants.

D. The factor that triggers a circuit breaker.

A

C. A method by which utilities attempt to reduce the need for new power plants.