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Modern Refrigeration Study Material > 12 - Basic Electrical Theory > Flashcards

12 - Basic Electrical Theory Flashcards

1
Q

What are Atoms?

A

Atoms are the smallest part of any element and are, therefore, the basic building blocks of all matter.

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2
Q

What is a nucleus?

A

The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom.

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3
Q

What are protons, electrons, and neutrons?

What distinguishes electrons from protons and neutrons?

A

Electrons - negative charge.
Protons - positive charge.
Neutrons - neutral charge.

Neutrons orbit around the nucleus, while protons and neutrons contract the nucleus.

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4
Q

What do these configurations of atoms mean?

1: Same number of protons and electrons.
2: An atom has an imbalance of electrons and protons
3: An atom has more electrons than protons
4: An atoms has more protons than electrons

A

1: Neutral charge
2: Ionized
3: Negatively charged ion
4: Positively charged

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5
Q

What will a negatively charged ion do when adjacent to another atom?

A

It will give up its extra electron to the adjacent atom, which will then become negatively charged. The new negatively charged atom will then perform this same process with the next atom, creating a chain reaction.

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6
Q

What is potential difference?

A

The push created by a difference in atomic charges. Also known as voltage or EMF (electromotive force)

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7
Q

What is voltage?

A

The electrical force or electrical pressure that a power source can generate.

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8
Q

What is the measurement of one volt?

Ex: how many amperes of current can a 9 volt battery send through a resistance of one ohm?

A

It is the amount of EMF required to send one ampere of current through a resistance of one ohm.

(EX: 9 volt battery can send 9 amperes of current through a resistance of one ohm)

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9
Q

What is current?

What is its measurement?

A

Current is the flow of electrons.

It is measured using a unit called an ampere. One ampere is equal to the flow of one coulomb per second.

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10
Q

What is a coulomb?

A

It is a measurement of the electrical charge in 6.24 X 10^18 electrons.

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11
Q

What happens to current when voltage increases, and vise versa?

A

They will both increase simultaneously, assuming electrical resistance is unchanging.

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12
Q

What is resistance?

What is it measured in?

A

It is the name of the electrical property that expresses how much a material resists the flow of electrons through it.

It is measured in ohms. An ohm is equal to the resistance that allows one volt to push one ampere of current through a circuit?

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13
Q

What are resistors? What are they usually made of?

A

Components designed to offer specific levels of resistance. Usually are made of carbon.

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14
Q

How is electrical energy expended when it passes through a high resistance material?

A

It generates heat.

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15
Q

What is Ohm’s Law?

What is the resistance of a lamp that draws 2 A at 120 v?

A

E (volts) = I (amps) x R (ohms)

60 ohms.

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16
Q

Due to ohms law, what will happen to a 120 v motor when it is wired up to a 240 v circuit, assuming the resistance remains the same.

A

Because current and voltage are directly related, the 240 v when ran through the 120 v motor will result in twice the amount of normal current, which will exceed the mfg specs. This will trip breakers and burn up winding insulation.

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17
Q

What is capacitance?

What is its unit of measurement?

A

It is the ability of a material to store a charge of free electrons or electrical energy in an electrostatic field.

It is measured in farads, which is the charge of one coulomb on a capacitors surface with a potential difference of one volt.

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18
Q

What are capacitors?

A

Capacitors are devices that are specifically designed and used for their capacitance. They are composed of two metal surfaces (aluminum) separated by an insulating material called a dielectric (mica, paper, oil, ceramic)

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19
Q

What is the difference between static and current electricity?

A

Static electricity is defined as the accumulation of an electric charge, such as in a capacitor.

Current electricity is electricity flowing through conductors.

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20
Q

What will happen when objects with positive and negative static charges interact with each other?

A

Objects with similar charges will repel each other. Objects with different charges will attract each other.

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21
Q

What is direct current?

A

It is electron flow along a conductor in one direction.

22
Q

Which type of current do batteries produce?

A

Direct current

23
Q

How can DC current be created?

A

By using a rectifier, which converts AC to DC voltage. By using an AC motor to power a DC generator, or by operating a DC generator using a gasoline or diesel engine (car alternator)

24
Q

What is alternating current?

A

It is electron flow along a conductor first in one direction, then in the other. It switches direction at regular intervals. It can be graphed to form a sine wave.

25
Q

What is alternating current frequency of cycles per second measured in?

A

Hertz

26
Q

How is voltage represented in an AC circuit

A

Voltage starts at zero, positive voltage then flows in one direction, and negative voltage back in the other.

27
Q

What are the three kinds of electrical materials?

A

Conductors: Materials that allow electrons to flow easily. Most are made of metal. They have atoms with free electrons in their structure.

Insulators: Materials that resist electron flow. They have virtually no free electrons.

Semiconductors: Materials that are ordinarily insulators, however, under certain conditions, can be made to conduct electricity.

28
Q

What does the term “solid-state” refer to?

A

It refers to the way solid-state electronics, which are made of semiconductors, can switch from insulator to conductor without moving parts.

29
Q

What is an SCR?

A

An SCR (silicone controlled rectifier) is a type of electronic switch that does not conduct electricity until it is triggered by a certain voltage level.

30
Q

What is an electrical circuit?

What are its three main components?

A

It provides a complete path for electrons to follow.

A power source
Conductors
Electrical load

31
Q

What is an electrical load?

A

Any device that consumes electricity to perform work.

32
Q

What is the difference between a closed and an open circuit?

A

A closed circuit allows electrons to flow from the power source and return back to it.

Open circuits mean the flow has been open or disconnected, and current cannot flow.

33
Q

What is a series circuit?

A

A circuit that only has a single path for current to flow. Commonly used for safety circuits.

34
Q

What is a parallel circuit?

A

It allows current to flow to and from a power source along two or more electrical paths, each of which has only one electrical load. The current changes based on the resistance of each load.

35
Q

What the difference in voltage and amperage between series and parallel circuits?

A

The current is the same across each load in a series circuit, but the voltage is the same in a parallel circuit.

36
Q

What is a series parallel circuit?

A

It has some electrical loads in series and some in parallel.

37
Q

What is a voltage drop?

A

It is the voltage applied across an electrical load that is causing current to flow through it.

38
Q

What are the four main causes of voltage drop?

A
  1. Undersized conductors
  2. Poor connections
  3. Higher than design circuit current
  4. Long conductors
39
Q

What is magnetic flux?

A

Lines of magnetic force connecting the north and south poles of a magnet.

40
Q

What is a magnetic field?

A

The space in which a magnetic force is operating.

41
Q

What is Induced Magnetism

A

It refers to any material that is capable of being magnetized when placed inside a magnetic field

42
Q

What is electromagnetism?

A

It refers to a conductor becoming surrounded by a magnetic field when current passes through it.

43
Q

What is an Electromagnet?

How is one formed?

A

It is an object that exhibits a magnetic field when current passes though it.

It is formed by wrapping a conductor (usually copper) around a soft iron core

44
Q

What four factors determine the strength of an electromagnet?

A
  1. The number of turns in the winding
  2. The strength of the current
  3. The core material and construction
  4. The length of the coil
45
Q

What is a slip ring?

A

It is a cylindrical piece of electrically conductive material that rotates with the wire loop in an AC generator/motor

46
Q

What is a commutator?

A

It is a split slip ring that forces the current to flow in one direction only, generating direct current in a generator.

47
Q

What is the difference between a slip ring and a commutator?

A

The slip ring is a continuous ring, whereas the commutator is segmented. In AC motors, slip rings are employed to enable a continuous power transfer, but in DC motors, commutators are used to reverse the polarity of the current in the armature windings.

48
Q

What is a transformer?

A

It transfers an alternating current from one coil of wire to another coil of wire through a magnetic field. It does this through induction

49
Q

What is induction?

A

The process of transferring electricity using a magnetic field.

50
Q

How are the primary and secondary coils utilized in a transformer?

A

The primary coil receives power from an AC electrical source and generates a magnetic field.

The secondary coil picks up this magnetic field, and converts it back into electricity.

51
Q

How many volts will a transformers secondary coil output, if the primary coil is fed 100 volts, and has double the amount of turns than the secondary coil?

A

50 volts

52
Q

What is the difference between a step down and a step up transformer

A

A step up transformer will increase the voltage supplied at the primary coil, and a step down transformer will decrease it.

Modern Refrigeration Study Material (11 decks)

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