1-1) DC-Terms

Question 1

Definition: direct current (DC)

Answer 1

Direct Current is defined as the flow of electronics in one direction through a circuit with constant voltage and current.

Question 2

What is Farday’s Law?

Answer 2

Electrical current will flow in a circuit provided that: there exists an electrical difference of electrical potential and; there is a complete path for current to flow.

Question 3

What is the direction of current flow in a DC circuit?

Answer 3

The direction of current flow is from a negative electrical potential to the opposite end that has a positive one.

Question 4

What is the negative ground concept?

Answer 4

In America, we use the negative ground concept for current flow where electromotive force (EMF) is flowing from a negative potential to a positive one.

Question 5

Definition: atoms

• what they are
• what they are made of
• electrical potential of its components

Answer 5

Atoms represent the smallest elements that exist in nature.
They represent the building blocks from which all other elements are made.
Most atoms are made up of 3 components: protons, neutrons and electrons.
The nucleus is the center of the atom made of protons and neutrons.
Electrons orbit the nucleus at the speed of light.
Electrical potential attracts the electrons to the nucleus.

Question 6

What are protons? Where are they found? What is their electrical potential? What is their role in the conduction of electricity?

Answer 6

Protons are positively charged subatomic particles that exist within the nucleolus of all atoms.
Protons contain a positive electrical potential.
Since protons cannot leave the nucleus, they are not involved in the conduction of electricity.
Their positive charges do affect the orbits of electrons around them.

Question 7

What are neutrons? Where are they found? What is their electrical potential? What is their role in the conduction of electricity?

Answer 7

Neutrons are neutral subatomic particles that exist within the nucleolus of all atoms.
They have no electrical effect on the atom, however they are important elements in the building blocks of all matter.
Being electrically neutral, neutrons are not involved in the conduction of electricity.

Question 8

What are electrons? Where are they found? What is their electrical potential? What keeps them attached to the atom? What is their role in the conduction of electricity?

Answer 8

Electrons are negatively charged subatomic particles that are located and travel around (orbit) the nucleus in an imaginary sphere or shell at the speed of light.
The speed of rotation combined with the electrical potential of the nucleus keeps the electrons in their orbits.

Question 9

What are the characteristics of a good conductor?

Answer 9

A good conductor is one that easily permits the movement of electrons from an electrical source to a load and back to the electrical source with a minimum of resistance.

Question 10

How do valence electrons factor into the conduction of current?

Answer 10

When the numbers of valence electrons in adjacent atoms are all the same, the atom is electrically neutral. As long as there is no difference of electrical potential between the atoms, current cannot flow.
When one atom gains a valance electron, it become more negative relative to the atom next to it, which is now more positive.
The second atom will then “attract” the extra electron while the first wants to get rid of its “incorrect” number of electrons in orbit. This causes the first electron to flow into the next atom’s valence orbit.

Question 11

What factors determine that amount of current that can flow in a conductor?

Answer 11

Cross-sectional area
Length
Temperature
Conductor material

Question 12

What is the difference between a conductor and an insulator?

Answer 12

Conductors are elements that don’t hang onto their valence electrons very well.
Insulators are elements that retain their valence electrons very well no matter the amount of force that is applied.

Question 13

What is an insulator and what are the key characteristics for an electrical insulator?
What are some examples of insulators?

Answer 13

An insulator is a material or device used to prevent the passage of heat, electricity or sound from one medium to another.
Electrical insulators do not allow their valance electrons to move from atom to atom.
Glass, mica and silica are all examples of insulators.
Air is also a good insulator, but can be jumped by a spark when enough electrical force is applied.

Question 14

What is static electricity? Where is it found? How is it generated? How is it released?

Answer 14

Static electricity is an electrical charge that may be built up on a non-conductive surface by friction.
Friction manually removes free electrons from a surface, and those electrons can combine until the charge is very large.
This creates a different of electrical potential that is held until contact is made to equalize the different charges.
when the charge is equalized by discharging, there can be a very large discharge–lightning is a good examples.

Question 15

What is the role or place of static electricity in aviation?

Answer 15

Static electricity serves no useful purpose in aviation. Static electricity discharges cause millions of dollars in damage every year to electronic equipment and aircraft structures.

Question 16

What is voltage?

Answer 16

Voltage is electric potential energy per unit charge. Often referred to as “electric potential,” which must be distinguished from “electromotive force” (EMF). “Electrical potential” is a per-Unit charge quantity.

Question 17

What is the unit of voltage?

Answer 17

Voltage is measured in “volts,” which is equal to joules per coulomb.

Question 18

What is a Coulomb and what is it equal to?

Answer 18

A Coulomb is a basic unit of electrical quantity. A Coulomb is equal to 6.28 billion-billion electrons. Not to be confused with EMF. A Coulomb is the actual count of electrons in a unit of measure.

6. 28 quintillion
7. 28x10^18

Question 19

What is a Joule? What component might use Joule as its measurement?

Answer 19

Not to be confused with a Coulomb, a Joule is the measure of actual electrical potential that is stored in an electrostatic field. Energy stored in a capacitor, for example, is energy stored in Joules.

A Joule is the amount of electrons in a suspended state as compared to some electrons in an adjacent part of the circuit.

Joules do NOT apply to a battery because that energy is stored chemically.

Question 20

What is EMF (E)? What units is EMF measured in?

Answer 20

Electromotive Force is the force required to move an electron.
EMF is measured in volts.
EMF is the force required to cause one amp of current to flow through one ohm of resistance.
EMF is interchangeable with volts and electrical energy.

Question 21

What are 3 methods to generate EMF?

Answer 21

1. Mechanically
2. Chemically
3. Friction

Question 22

What is a Volt (V)? How is it often expressed?

Answer 22

A volt is a basic unit of measure of electrical pressure.

A volt is the amount of force required to cause one amp of current to flow through one ohm of resistance.

Voltage is often expressed as: voltage, voltage drop, potential different, EMF, IR drop of the symbol “E.”

Question 23

What is electrical current?

Answer 23

Current is the flow of electricity. Electrical current is the flow of electrons that pass a given point in a specific amount of time.

Question 24

What is electrical current’s unit of measurement?

Answer 24

Current for electricity is measured in Amps and symbolized by the letter “I.”

Question 25

What is an Ampere (A, amp)? What symbol is it represented by? How much is 1 Amp?

Answer 25

It is the unit of measure used to express the flow of electrons (current).

In mathematical calculations, amps are represented as the symbol “I.”

Current must have a complete path back to its opposite power source (see also Faraday’s Law).

1 amp is the amount of current that can be forced through 1 ohm of resistance by the pressure of 1 volt.

Question 26

What is Resistance (R)?

Answer 26

Resistance is the electrical opposition to current flow in a conductor. This is the opposition that a circuit, component, or substance presents to the flow of electricity.

Resistance is the force that opposes or slows down another force, drops voltage or consumes power.

Question 27

What is the relationship between current (I) and resistance (R)?

Answer 27

Current and Resistance are inversely proportional. The higher the resistance in any circuit, the less current can flow at any given time.

Current will take the path of least resistance. When current flows in a parallel path between two unequal legs of a circuit, a larger amount of current will flow into the leg with the least amount of resistance.

Question 28

What is an Ohm?

Answer 28

Ohm is the unit of measurement of Resistance (R). Ohm is a mathematical unit of measure of electrical opposition to the current flow in a circuit. A circuit has one ohm of resistance when it limits the flow of current to 1 amp under 1 volt of pressure.

Question 29

What is Ohm’s Law?

Answer 29

V = IR

Voltage = Current x Resistance

The amount of current flowing in a circuit is directly proportional to the circuit voltage and inversely proportional to the circuit resistance. This is the basic formula for mathematically determining numerical values of items in the circuit. Voltage equals the electrical current times the resistance.

By knowing 2 variables, you can solve for the 3rd.

Question 30

What is a Watt (W)? How is it calculated?

Answer 30

P=IE
Power = Current x Voltage
Watt is a basic unit of electrical power. It is calculated from the product of voltage and current.

Question 31

What is a series circuit?

Answer 31

A series circuit is one where current has only one path to flow from the source and back.

Question 32

What are the 5 rules of a series DC circuit?

Answer 32

1) The same current flows through each part of a series circuit.
2) The total resistance of a series circuit is equal to the sum of the individual resistances.
3) The total voltage across a series circuit is equal to the total sum of individual voltage drops.
4) The voltage drop across a resistor in a series circuit is proportional to the ohmic value of the resistor.

Question 33

What is a parallel circuit?

Answer 33

Parallel circuits are those that offer more than one path for current flow. Circuit components are connected directly to each other and the power supply.

Current is divided between each branch in the circuit. A parallel circuit contains two or more resistances not connected in series.

Question 34

What are the 5 rules of a parallel DC circuit?

Answer 34

1) The same voltage exists across each branch of a parallel circuit and is equal to the source voltage.
2) Current through each branch of a parallel circuit network is inversely proportional to the amount of resistance in that branch. In other words, if a given branch has more resistance, less current will flow through that branch.
3) Total current of a parallel circuit is equal to the sum of individual branch currents of the circuit.
4) Total resistance in a parallel circuit is NOT the sum of individual resistances. Total resistance in a parallel circuit is referred to equivalent resistance (Req).
5) Total power consumed in a parallel circuit is equal to the power consumed by individual components.

Question 35

What is a Series-Parallel Circuit and how does one solve it?

Answer 35

This type of circuit has both properties of a series and parallel circuit. For these circuits, each section needs to be worked to its simplest elements then reworked to fill in the unknowns.

Question 36

What is a capacitor?

Answer 36

A capacitor is an electrical component used to store electrical energy in the form of an electrostatic field.

Question 37

What is a capacitor made of and how does it work?

Answer 37

A capacitor is made from two parallel conductors separated by an insulator called the dialectric. As DC is applied to one of those plates, the voltage will charge in the device based on the various electrical properties.

Current will then be depleted by a discharge off of the charged plate when a path for current flow to the other side of the plate is present.

Question 38

What is the fundamental electrical property of a capacitor with respect to DC and AC voltage?

Answer 38

A capacitor will block DC voltages and pass AC voltages.

Question 39

What is a battery?

Answer 39

A device made of one or more individual electrochemical cells used to store chemical energy and make the energy available in electrical form.

Question 40

What is the difference between a primary and secondary battery?

Answer 40

Primary batteries cannot be recharged by need to have the electrolytes replaced. Secondary batteries can be recharged because the application of a voltage can release the electrons back into solution, effectively recharging the battery. Batteries store DC power.

Question 41

What is magnetism?

Answer 41

Magnetism is the ability of a magnet to attract certain materials containing iron and other ferrous materials. Magnetism also describes a force of energy than can influence the flow of electrons.

Question 42

What is magnetic flux?

Answer 42

Lines of flux exist around magnets that travel from the north end of the magnet to the south end.

Question 43

What are the 5 basic rules of magnetic flux?

Answer 43

1) Flux takes the most direct path to the opposite pole.
2) Lines of flux never cross.
3) Lines of flux travel from north to south poles.
4) Lines of flux can only pass through permeable material.
5) Unlike poles attract lines of flux and be repelled by like poles.

Question 44

What is magnetic permeability? What is it a ratio of?

Answer 44

The measure of easy that lines of magnetic flux travel through a material. The measurement is based on the ratio of magnetic flux density in a substance to the magnetizing force that produces it. Only certain materials can pass or redirect magnetic lines of flux.

Question 45

What is a magnetic field and how is its strength determined?

Answer 45

When current flows in a conductor, a magnetic field is produced around the conductor. The strength of that magnetic field is directly proportional to the amount of current that is flowing in the conductor.

Question 46

How do magnetic fields produced from DC and AC currents differ?

Answer 46

When a DC voltage is applied to a conductor, the magnetic field will remain stationary around the conductor. When an AC voltage is applied, the magnetic field will expand and contract at the same rate as the applied AC frequency.

Question 47

What is Counter EMF or Back EMF? Where does it come from?

Answer 47

EMF is the voltage applied to a conductor, so counter or back EMF is the voltage that opposes the applied EMF.

Condition normally exists in circuits that have an AC voltage applied. When a voltage is removed, the collapsing magnetic field will produce a voltage back into the circuit in the opposite direction of the applied voltage.

Question 48

What is the Left-hand rule used for?

Answer 48

This refers to generators but can be applied to motors. To produce EMF in a conductor, you pass a conductor across magnetic lines of flux. The motion of the conductor cutting magnetic lines of flux causes electrons to move in the conductor.

The left-hand rule is used to determine the direction of movement of electrons in a current-carrying conductor in a magnetic field.

Question 48

What is the Left-hand rule used for?

Answer 48

This refers to generators but can be applied to motors. To produce EMF in a conductor, you pass a conductor across magnetic lines of flux. The motion of the conductor cutting magnetic lines of flux causes electrons to move in the conductor.

The left-hand rule is used to determine the direction of movement of electrons in a current-carrying conductor in a magnetic field.

Question 49

What is a Henry (H)?

Answer 49

This is the basic unit of measurement for induction. A Henry represents the inductance of a coil if 1 volt of induced EMF is produced when the current is changing at the rate of 1 ampere per second. An inductor stores energy in a surrounding magnetic field and returns the energy in the form of current to the circuit when the magnetic field collapses.

Voltage across an inductor is proportional to the rate of change of current.

Question 50

What is a Farad (F?)

Answer 50

The unit of measurement for capacitance in a capacitor.  Capacitance is determined by the number of electrons that can be stored in a capacitor for each volt of applied voltage. 
 The Farad (F) is the unit of capacitance.  

1 Farad represents a charge of 1 coulomb that raises the potential 1 volt.

Question 51

What factors determine capacitance?

Answer 51

1) Material used as a dialectric–the larger the dialetric constance, the greater the capacitance.
2) The area of the plates in the capacitor. The larger the plate area, the greater the capacitance.
3) The distance between the plates. The smaller the distance between the plates, the greater the capacitance.

Question 52

What part of an atom is associated with the flow of electricity?

Question 53

What electronics in a conductor determines whether its flow is poor or good?

Question 54

What is the definition of static electricity?

Question 55

What term is used to express the flow of electricity?

Question 56

What is the definition of a Coulomb?

Question 57

What is the basic unit of electrical pressure? What other names could it go by?

Question 58

If voltage and resistance are known, describe how total current can be determined. What is the equation?

Question 59

What device other than an actual battery can be used to store electricity?

Question 60

Describe the left hand rule as it pertains to electrical generation.