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General Explanations (Written) > Basic Electrical > Flashcards

Basic Electrical Flashcards

1
Q

Working Voltage

A

The highest voltage that can be steadily applied to a capacitor without the danger of the dielectric breaking down.

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2
Q

Working voltage depends upon what?

A

The material used as the dielectric and on its thickness.

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3
Q

What are the three types of resistive forces in an AC circuit? (also known as Impedance)

A

Inductive reactance - causes current to lag the voltage.
Capacitive reactance - causes current to lead the voltage.
Resistance - allows current and voltage to remain in phase.

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4
Q

Inductive and capacitive reactance are how many degrees out of phase?

A

180 degrees, canceling each other out.

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5
Q

Inductive reactance

A

The continuously inducted voltage opposition to the current in a circuit caused by an electromagnetic field (EMF).

/or, the measure of how much the countering EMF in the circuit will oppose current variations.

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6
Q

What units are inductive reactance measured in?

A

Ohms - same as resistance.

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7
Q

Dielectric field

A

The field of force that exists around a charged body (sometimes called an electrostatic field), represented by lines extending in all directions from the charged body, and terminating where there is an equal and opposite charge.

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8
Q

How do transformers work?

A

The changing current in the primary windings produces a changing magnetic field whose flux cuts across the turns of the secondary winding and induces a voltage into it.

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9
Q

8004

A

return to this card

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10
Q

Which of the five items listed have an effect on inductive reactance, and which do not have an effect?

Inductance
Voltage
Capacitive reactance
Frequency
Resistance

A

Have an effect:
Inductance
Frequency

No effect:
Voltage
Capactive reactance
Resistance

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11
Q

Total capacitance formulas in series vs in parallel

A

In series:

C(T) = 1 / ( (1/C(1)) + (1/C(2)) + (1/C(3))…)

In parallel:

C(T) = C(1) + C(2) + C(3)…

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12
Q

How do capacitors behave in response to the amount of electrons present in a circuit?

A

Capacitors accept electrons when there is an excess and release them back into the circuit when the values decrease.

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13
Q

What do capacitors store?

A

electrical charges.

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14
Q

Effective Voltage

A

Also known as root mean square (rms) voltage, effective voltage is the voltage measured by most of the AC voltmeters.

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15
Q

What instruments measure peak voltage?

A

A special peak voltmeter or an oscilloscope.

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16
Q

What three factors affect the amount of electricity a capacitor can store?

A

The area of the plates: the larger the plate area, the greater the capacity

The thickness of the dielectric: the closer the plates are together, the stronger the electrical field will be and the greater the capacity.

The material from which the dielectric is made: the higher the dielectric constant, the greater the capacity.

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17
Q

Metric Prefixes / Powers of Ten

A

Exa (E) = 10^18
Peta (P) = 10^15
Tera (T) = 10^12
Giga (G) = 10^9
Mega (M) = 10^6
kilo (k) = 10^3
hecto (h) = 10^2
deca (da) = 10^1

deci (d) = 10^-1
centi (c) = 10^-2
milli (m) = 10^-3
micro (Greek symbol pronounced “mu”) = 10^-6
nano (n) = 10^-9
pico (p) = 10^-12
femto (f) = 10^-15
atto (a) = 10^-18

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18
Q

Effective values

A

Almost all measuring instruments used for electrical system servicing measure the effective rms values are assumed.

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19
Q

Total Inductance formulas in series vs in parallel

A

In series:

L(T) = L(1) + L(2) + L(3)…

In parallel:

L(T) = 1 / ( (1/L(1)) + (1/L(2)) + (1/L(3))…)

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20
Q

8015 through 8019

A

Math world problems. Review the study guide for their explanations.

Page 6

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21
Q

The power produced by an electric motor is the product of what?

A

Its current and voltage

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22
Q

What is the potential difference between two conductors?

A

The measure of the electrical pressure difference between the conductors.

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23
Q

Current flowing through a conductor produces what and dissipates what?

A

It produces a magnetic field and dissipates thermal energy

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24
Q

What is true power in an AC circuit?

A

the product of the circuit voltage and only that part of the current in phase with the voltage

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25
Q

What is apparent power?

A

the circuit voltage multiplied by all of the current.

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26
Q

What is a reactive circuit?

A

Any AC circuit containing either inductance or capacitance.

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27
Q

Impedance formula

A

Z (impedance) = square root of: ( R(resistance)^2 + ( X(L)(Inductive reactance) - X(C)(capactive reactance) )^2

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28
Q

Resistance formula in series vs parallel

A

In series:

R(T) = R(1) + R(2) + R(3)…

In parallel:

R(T) = 1 / ( (1/R(1)) + (1/R(2)) + (1/R(3))…)

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29
Q

How should ammeters be connected to a circuit?

A

In series

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30
Q

How should voltmeters be connected to a circuit?

A

In parallel

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31
Q

How much voltage drop is acceptable with a maximum current flow through a switch?

A

0.2 volts

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32
Q

General capacitance formula

A

C(capacitance) = Q(charge) / E(applied voltage)

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33
Q

What unit is capacitance measured in?

A

Farads

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34
Q

What unit is charge measured in?

A

Coulombs

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35
Q

When lights are connected in parallel across a voltage source, …

A

The voltage across each of the lights will be the same as the voltage of the source.

36
Q

Power dissipated in a resistor is found how?

A

By multiplying its resistance by the square of the current

P = I^2 x R

37
Q

Ohm’s Law Formulas

A

Resistance:

R = P / I^2
R = E^2 / P
R = E / I

Current:

I = E / R
I = P / E
I = sq.rt( P / R )

Voltage:

E = sq.rt( P x R )
E = P / I
E = I x R

Power

P = I x E
P = I^2 x R
P = E^2 / R

38
Q

Electrical power is measured in what unit?

A

Watt

39
Q

Electrical pressure is measured in what unit?

A

Volt

40
Q

Electrical current flow is measured in what unit?

A

Ampere

41
Q

One coulomb is equal to how many electrons?

A

6.28 x 10^18 electrons.

42
Q

Electrical quantity is measured in what unit?

A

Coulomb

43
Q

Kirchhoff’s current law states what?

A

The sum of the currents into a junction or node is equal to the sum of the currents flowing out of that same junction or node.

(A junction can be defined as a point in the circuit where two or more circuit paths come together)

44
Q

What are diodes?

A

Two element electronic components that act as electron check valves, allowing electrons to pass freely in one direction while blocking their flow in the opposite direction.

45
Q

What are rectifiers?

A

A device that transforms AC into DC by limiting
or regulating the direction of current flow.

46
Q

The continually changing current in an AC circuit causes a changing magnetic field to cut across conductors in an adjacent circuit. When the changing voltage field cuts across a conductor, it induces a voltage in it.

Induction allows electrical energy to be transferred from one circuit to another without the aid of electrical connections.

A

Transformers, amiright?

47
Q

In a series circuit, the voltage drop across each resistor is determined by what?

A

its resistance.

48
Q

The voltage of a battery is determined how?

A

By the number of cells connected in series to form the battery.

49
Q

A lead-acid cell is normally rated at approximately how many volts?

A

2 volts, although in reality one lead acid cell just removed from a charger is approximately 2.2 volts.

50
Q

In a parallel circuit, the more paths there are for the current to flow, the less resistance there will be.

What will happen to the resistance of a circuit if one of the paths is removed.

A

The resistance of the circuit will increase, as fewer paths remain for current flow.

51
Q

In a transformer, if the voltage in the secondary winding is four time that of the primary winding, what will happen to the current in the secondary winding?

A

In a transformer, the power in the secondary winding is equal to the power of the primary winding. Therefore, when the voltage is four times as great in the secondary, the current will be 1/4th of of the primary.

52
Q

The resistance of a conductor varies how with length, cross-sectional area, and resistivity?

A

The resistance of a conductor varies directly with its length, inversely with its cross-sectional area, and directly with the resistivity of the material.

53
Q

Magnetic permeability of a material

A

A measure of the ease with which lines of magnetic force can pass through a material.

Ex. Iron has the highest permeability of copper, iron, and aluminum.

54
Q

Voltage drop across a circuit is determined by what?

A

The resistance of the circuit and the amount of current flowing through it. (Ohm’s Law)

55
Q

Thermal switch

A

Another name for a built-in thermal circuit breaker, which is a circuit protection device that opens the circuit when the windings of the motor get too hot.

56
Q

8057-8071

A

Wiring diagram figure questions. Refer to pages 15-20 in the study guide.

57
Q

(Figure 20 - pg. 21) An open in the resistor causes how much resistance?

A

Infinite resistance. No current can flow in the circuit.

58
Q

(Figure 21 - pg. 21) Resistors symbols

Resistor 1 is what type?
Resistor 2 is what type?
Resistor 3 is what type?

A

Resistor 1: tapped resistor
Resistor 2: variable resistor (specifically a rheostat)
Resistor 3: tapped resistor that is tapped at two places

59
Q

What is a transistor?

A

A three-terminal device primarily used to amplify signals and control current within a circuit. Through a transistor, you can use a small amount of current to control a large amount of current.

60
Q

What are the three pins that make up a transistor?

A

The emitter, base, and collector

61
Q

8075 and 8076 and 8078

A

21 22

62
Q

What is a zener diode?

A

a special type of semiconductor diode that is designed to operate with current flowing through it in its reverse direction.

When a specific amount of inverse voltage is applied between the cathode and anode. the diode breaks down and conducts in its reverse direction.

This principle is used as the voltage-sensing element in a voltage regulator

63
Q

When a solid-state device such as a diode is forward biased, how are the n and p type materials configured?

A

The n-material is negative with respect to the p-material

64
Q

N-type vs P-type doped semiconductors

A

N-type is when a semiconductor has an extra electron in its valence shell

P-type is when a semiconductor lacks an electron in its valence shell

Placing an N-type (-) and P-type (+) semiconductor beside one another (creating a PN or NP junction) and connecting it to a voltage source, causes a flow of electron from the N-type with the extra electron to the P-type that needs that electron.

This is the fundamental principle behind diodes and transistors.

Highly recommend watching this video for more complete information:

https://www.youtube.com/watch?v=Fwj_d3uO5g8&t=402s

https://www.youtube.com/watch?v=J4oO7PT_nzQ&t=311s

65
Q

If there is a 1 on any of the inputs of an “or” logic gate, what will be your output?

A

1

66
Q

If there is a 0 on any of the inputs of an “and” logic gate, what will be your output?

A

0

67
Q

If there is only a single 1 on the input of an “x-or”gate, what will be the output?

A

1

If there is more than one 1 in the inputs, it will have an output of 0.

…Yeah, I know. Just go look up refresher on logic gates. Flash cards are not the right format for this stuff.

68
Q

What is the electrolyte in a lead-acid battery?

A

A solution of sulfuric acid and water.

69
Q

What must be taken into consideration when testing the specific gravity of the electrolyte of a lead-acid battery?

A

The temperature. No correction is necessary between 70 and 90 degrees Fahrenheit.

70
Q

A correction of how much should be added to the specific gravity reading of a lead-acid battery electrolyte above 90 degrees Fahrenheit?

A

A correction of 0.4 should be added to the specific gravity reading for each 10 degrees above 80 degrees Fahrenheit (starting at 90 degrees)

71
Q

A correction of how much should be added to the specific gravity reading of a lead-acid battery electrolyte below 70 degrees Fahrenheit?

A

A correction of 0.4 should be subtracted from the specific gravity reading for each 10 degrees below 80 degrees Fahrenheit (starting at 70 degrees)

72
Q

When a lead acid battery is charged, what occurs inside the battery?

A

The sulfate radicals from both plates join with hydrogen atoms from the water in the electrolyte and form sulfuric acid.

73
Q

What has a lower freezing point, sulfuric acid or water?

A

Sulfuric acid.

The electrolyte in a fully charged battery has a freezing point much lower than that of the electrolyte in a discharged battery.

74
Q

What happens when a battery is charged using the constant-voltage method?

A

a voltage somewhat higher than the open-circuit voltage of the battery is placed across the battery terminals.

When the battery is in a low state of charge, its voltage is low and the constant-voltage charger will put a large amount of current into it.

As the charge continues, the battery voltage rises and the current going into the battery decreases.

When the battery is fully charged, only enough current flows into it to compensate for the power lost in its internal resistance.

75
Q

How are Nickel-cadmium batteries different from lead-acid batteries?

A

The cells of a Nickel-cadmium battery are removable and are connected together with metal straps secured to the tops of the cells with nuts.

76
Q

What will happen to a Nickel-cadmium battery if the cell-link connections are not properly torqued?

A

They will cause a high-resistance path for the current. They will become overheated and will show burn marks.

77
Q

What happens when a Nickel-cadmium battery becomes fully charged?

A

the battery becomes hot and the electrolyte bubbles, causing some of the electrolyte to spew out of the top of the cell through the cell vent.

When the water evaporates from the spewed-out electrolyte, it leaves a deposit of potassium carbonate, a white powder.

78
Q

Lead-acid and nickel-cadmium batteries require separate charging stations, cleaning facilities, and installation tools because why?

A

The chemistry of the two batteries are incompatible and will contaminate one another.

79
Q

What happens to the electrolyte and plates of a nickel-cadmium battery when it is fully discharged?

A

The plates absorb some of the electrolyte.

80
Q

Why do nickel-cadmium batteries emit gas towards the end of their charging cycle?

A

because of the decomposition of the water in the electrolyte into hydrogen at the negative plates and oxygen at the positive plate.

81
Q

The end-of-charge voltage of a nickel-cadmium battery depends on what?

A

The temperature and the method used for charging.

82
Q

Does the specific gravity of the electrolyte of a nickel-cadmium battery change as the state-of-charge changes?

A

No.

The only way to know for sure the amount of charge of a nickel-cadmium battery is to completely discharge it, then to put back into it a known number of ampere-hours of charge.

83
Q

What will happen when water is added to a nickel-cadmium battery when it is not fully charged?

A

The electrolyte level will be too high when the battery is fully charged, causing the excess liquid to spew out of the cell.

84
Q

What is one of the desirable features of a nickel-cadmium battery?

A

Its low internal resistance which gives it the ability to discharge at a high rate and to accept a high rate of charge.

85
Q

When the cell temperature of a nickel-cadmium battery increases, what happens to the voltage and internal resistance?

A

They decrease.

This allows the battery to accept an excessive amount of charging current which produces more heat and can cause thermal runaway.

86
Q

When does thermal runaway occur in a nickel-cadmium battery?

A

During a high current discharge/charge rate in a constant potential charging system.

General Explanations (Written) (12 decks)

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