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Electrical Principles Flashcards

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1
Q

What are the two points of view on electricity?

A

The scientist seeks to explain its mysteries; the engineer seeks to make use of its properties.

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2
Q

What are the four categories of electrical engineering?

A
  • The production of electrical energy
  • The transmission of electrical energy
  • The application of electrical energy
  • The control of electrical energy
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3
Q

What is the function of the source in an electrical system?

A

To provide the energy for the electrical system.

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4
Q

What is the function of the load in an electrical system?

A

To absorb the electrical energy supplied by the source.

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5
Q

What does the transmission system do in an electrical system?

A

It conducts the energy from the source to the load.

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6
Q

What is the function of the control apparatus in an electrical system?

A

To control the flow of energy.

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7
Q

What is the term for the energy transport from the source to the load?

A

Transmission.

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8
Q

What is an electrical circuit diagram used for?

A

To show a clear sequence of events in an electrical system.

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9
Q

What does the International Electrotechnical Commission (IEC) publish regarding electrical symbols?

A

A specification system for symbols used in electrical diagrams.

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10
Q

What are the two forms of electricity by convention?

A

Negative and positive electricity.

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11
Q

What is an ion?

A

A charged atom.

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12
Q

What is the conventional direction of current flow?

A

From positive to negative.

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13
Q

What is the term for the driving influence that causes current to flow?

A

Electromotive force (e.m.f.).

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14
Q

What is the unit of current?

A

Ampere (A).

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15
Q

How is the ampere defined?

A

The current that produces a force of 2 × 10−7 newtons per metre between two parallel conductors.

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16
Q

What is the unit of electrical charge?

A

Coulomb (C).

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17
Q

What is the relation between charge (Q), current (I), and time (t)?

A

Q = I × t.

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18
Q

What is the unit of potential difference?

A

Volt (V).

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19
Q

What does voltage originally mean?

A

A difference of potential expressed in volts.

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20
Q

True or False: Electrons are negatively charged particles.

A

True.

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21
Q

Fill in the blank: A material that does not readily permit electron flow is termed an _______.

A

insulator.

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22
Q

What is the term for the energy transferred due to the passage of unit charge between two points?

A

Potential difference (p.d.).

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23
Q

What happens when electrons move in a concerted manner?

A

It is termed electric current flow.

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24
Q

What must be fulfilled for current flow to continue in a circuit?

A
  • There must be a complete circuit
  • There must be a driving influence (e.m.f.)
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25
What is the difference between e.m.f. and p.d.?
E.m.f. is always active in producing current; p.d. may be passive or active.
26
What is the common practice regarding the term 'current'?
It is used to indicate both a flow of charge and the rate of flow of charge.
27
What type of current is delivered by a battery?
Direct current (d.c.).
28
What is the unit of potential difference?
Volt (V) ## Footnote The potential difference is defined as the difference of potential between two points of a conducting wire carrying a current of 1 ampere when the power dissipated is equal to 1 watt.
29
What does the term 'voltage' originally mean?
A difference of potential expressed in volts ## Footnote It is now used synonymously with potential difference irrespective of the unit.
30
What is the relationship expressed by the equation P = VI?
Power is equal to potential difference multiplied by current.
31
What is the unit of electric resistance?
Ohm (Ω) ## Footnote It is defined as the resistance between two points of a conductor when a potential difference of 1 volt produces a current of 1 ampere.
32
What is Ohm's law?
V ∝ I ## Footnote This law states that the potential difference across a conductor is proportional to the current flowing through it, provided temperature remains constant.
33
What is the formula for electric resistance in relation to voltage and current?
V = IR
34
What is the definition of electromotive force (e.m.f.)?
The force that tends to produce an electric current in a circuit.
35
What are the principal sources of electromotive force?
* Electrodes of dissimilar materials in an electrolyte (batteries) * Relative movement of a conductor and magnetic flux (electric generators) * Difference of temperature between junctions of dissimilar metals (thermo-junctions)
36
What is the formula for power dissipated in a resistor?
P = I^2 R
37
What does the symbol 'R' represent in electrical equations?
Resistance
38
Fill in the blank: The energy dissipated in a resistor can be calculated using the formula W = Pt = _______.
I^2Rt
39
True or False: All resistors have a power rating that indicates the maximum power they can dissipate without damage.
True
40
What is the common standard power ratings for resistors in electronic circuits?
* 1/4 W * 1/2 W * 1 W * 2 W
41
What is the effect of temperature on resistors?
All resistors dissipate heat when operating, which can affect their resistance.
42
What are the two types of resistors based on their resistance characteristics?
* Linear resistors * Non-linear resistors
43
What is a potentiometer?
A variable resistor with three connections used to vary resistance.
44
How is the resistance value indicated on carbon resistors?
By color bands painted around the resistors.
45
What is the significance of the fourth band on a resistor?
It indicates the tolerance of the resistor's resistance value.
46
Fill in the blank: A resistor with bands of orange, blue, and green has a resistance of _______.
3,600,000 Ω
47
What do the first three bands of a resistor indicate?
The resistance value in Ohms (Ω) ## Footnote Each color corresponds to a specific digit and multiplier, determining the resistance value.
48
In the resistor color code, what does the fourth band represent?
The tolerance of the resistor ## Footnote Tolerance indicates the variation in the actual resistance value from the nominal value.
49
What does a silver fourth band indicate for a resistor?
A tolerance of ±10% ## Footnote This means the actual resistance can vary by 10% from the nominal value.
50
What is the purpose of a fifth band on some resistors?
To indicate a reliability factor ## Footnote This factor shows the percentage of failure per 1000 hours of use.
51
What percentage of failure does a brown fifth band indicate?
1% ## Footnote This means one in every hundred resistors may fail within 1000 hours.
52
How is resistance marked on small or oddly shaped resistors?
Using a letter code ## Footnote This code simplifies the identification of resistance values.
53
What is the resistance value for a resistor marked with the code 4K7?
4.7 kΩ ## Footnote The 'K' signifies kilohms.
54
What is the resistance range for a resistor with bands Brown, Black, and Orange?
Between 8 kΩ and 12 kΩ ## Footnote The nominal value is 10 kΩ with a tolerance of ±20%.
55
What are the two categories of materials based on their ability to conduct electricity?
* Conductors * Insulators
56
Which material is considered the best conductor?
Copper ## Footnote Copper is widely used in electrical wiring due to its excellent conductivity.
57
What is the primary function of conductors in an electrical circuit?
To provide a complete circuit for current flow ## Footnote Conductors contain free electrons that allow current to pass.
58
What happens in a short-circuit condition?
The resistance is at its lowest value of 0 Ω ## Footnote This results in no limit to the current flow.
59
What is an open-circuit condition?
A circuit with infinite resistance ## Footnote No current can flow if the circuit is open.
60
What is the main source of electricity in the UK?
Generating stations operated by electricity suppliers ## Footnote These stations generate electricity using various methods, including steam and hydroelectric power.
61
What is the difference between primary cells and secondary cells?
* Primary cells: non-rechargeable * Secondary cells: rechargeable
62
What types of devices typically use primary cells?
* Torches * Transistor radios * Hearing aids * Cameras * Watches * Cars
63
What is the disadvantage of using primary cells?
They are expensive for the amount of energy provided ## Footnote Convenience often justifies the cost.
64
What is the effect of materials with sizeable energy gaps in electrical circuits?
They are used to insulate the circuit ## Footnote These materials contain the current within the conductors.
65
What is thevenins theorem?
The current in any branch of a network is that which would result if an e.m.f. equal to the p.d. across a break made in the branch, were introduced into the branch, all other e.m.f.s being removed and represented by the internal resistances of the sources
66
What is nortons theorem?
The current that flows in any branch of a network is the same as that which would flow in the branch if it were connected across a source of electrical energy, the short-circuit current of which is equal to the current that would flow in a short-circuit across the branch, and the internal resistance of which is equal to the resistance which appears across the open-circuited branch terminals

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