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ELECTRICAL ENGINEERING PRINCIPLES LET > Electrical > Flashcards

Electrical Flashcards

(55 cards)

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1
Q

What are the 3 main effects of current?

A
  1. Magnetic (relays,motors,generators)
  2. Heating (Cookers,water heater,electric fence)
  3. Chemical (Primary & secondary cells & electroplating)
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2
Q

Whats the difference between AC & DC?

A
  • DC -current flow in 1 direction in a constant magnitude
  • AC - current changes in 1 direction rising to maximum back to 0 then to maximum in other direction
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3
Q

Charge

What is current?

A

Flow rate of charge

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4
Q

What is Ohms law?

A

Current flowing through a conductor is directly proportional to the applied Voltage through it & inversely proportional to the Resistance providing temperature is constant

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5
Q

What does a fuse do?

A

Prevents overcurrent in a circuit,if the current exceeds the fuse melts breaking the circuit

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6
Q

Insulation resistance decreases due to…

A
  • Dampness
  • Brittleness with age
  • Accidental damage
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7
Q

If volatge is the same across all resistors in parallel,what is the current?

A

Current is different

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8
Q

In a series circuit the current is the same through each component,what is the voltage?

A

The voltage is different

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9
Q

Name 2 types of resistors & their uses

A
  1. Surface mount technology (SMT) used in electronics
  2. Wire wound used in motor starters & power circuits
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10
Q

Name 2 ways to identify resistors

A
  1. Colour coding
  2. Alpha numerical coding
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11
Q

R=pL/A

What 4 things affect resistance

A

1. Type of material
2. Length of conductor
3. Cross-sectional area of conductor
4. Temp of material

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12
Q

Name hazards with Capacitors

A

A charged capacitior can cause electric shock, need to discharge across a resistive load to make safe.

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13
Q

What does a capacitor consist of?

A

2 plates seperated by insulating material known as dialectric.

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14
Q

What is Kirchoffs current law?

A

Current going into a junction is always the same a current out

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15
Q

What is Kirchoffs Voltage law?

A

In any closed loop the amount of voltage drop = the total voltage

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16
Q

Series circuit/variable resistor

Describe a Rheostat

A
  • Variable resistor with 2 terminals,1 fixed &1 sliding
  • Controls current flow by changing resistance
  • Connected in series
  • Slider to left=max current
  • Slider to right=min current
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17
Q

Voltage

Describe a Potentiometer

A
  • Variable resistor ,3 terminals
  • Provides an adjustable voltage divider circuit,produces a variable p.d from fixed e.m.f
  • Slider left=V increase
  • Slider right=V decrease

dimmer switch,tv controls

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18
Q

What is Absolute potential?

A

Voltage with respect to earth

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19
Q

Name 3 things that determine capacitance

A
  1. Area of plate
  2. Thickness of dialectric
  3. Dialectric material
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20
Q

In paralell circuits what is the same over each capacitor?

A

Voltage

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21
Q

In series circuits what is the same over each capacitor

Q

A

Charge

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22
Q

In a capacitor how long does it take for voltage to reach steady state?

A

5T (5xtime)

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23
Q

Name 2 types of capacitors

Study These Flashcards
A
  1. Fixed
  2. Variable
24
Q

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~~~

Disadvantage of electrolytic capacitors?

Study These Flashcards
A

Used in DC circuits

25
Advantage of electrolytic capacitors
Larger capacitance
26
How to charge a capacitor
* Turn on switch,emf applied to capacitor * Electrons build up on 1 plate with neg charge,positive on other * Surplus of positive ions on one plate * No electron go through plate * Flow continues till capacitor is charged
27
What is Time constant?
Time it takes for capacitor to reach max charge if inital charge is maintained
28
Describe a magnetic field
Area around a magnet where magnetic force can be detected
29
What is Flux density measured in?
Tesla (T)
30
Describe magnetic flux
Amount of magnetic field produced by a magnetic source
31
In relation to magnetism, what is Reluctance?
Magnetic resistance to flux
32
# Magnetism Name 4 things that affect Force
1. Flux density 2. Current strength 3. Length of conductor 4. Direction of field + current
33
What happens when a current carrying conductor is placed in a magnetic field?
Field strong on one side of conductor, weak on other, the conductor moves outward | Application DC Motor , used in generators
34
Explain Self-Inductance
When EMF is induced in the same circuit in which current is charging
35
Explain Mutual-inductance
When EMF is induced in a circuit by a change in flux due to current charging in an adjacent circuit
36
Explain the principle of a generator
* Conductors form a circuit that move through mag field * EMF induced in conductor * Generators convert mechanical energy to electrical energy
37
Define electromagnetic induction
When a conductor is moved across a field,cutting the lines of flux it produces **EMF & current** in a conductor
38
# Back What is Lenz's law?
The changing current in a conductor induces a back EMF across it to oppose the motion which produces it
39
Name 3 factors that affect inductance
1. Number of turns of wire 2. Cross-sectional area of coil 3. Presence of mag core
40
In safety, **insulation** uses
Peak value
41
In safety, **fuses** use
RMS value
42
State 2 advantages to AC
* Easier to distribute * Cheaper to generate
43
What is the power rating of a transformer?
The Volt-Amperes that it can transform without overheating
44
What does Back EMF do?
Tries to stop changes in current, when current at max there are no changes so it drops to 0
45
What is the steady state current?
Max
46
What is the steady state Voltage?
0
47
What is inductive reactance?
Opposition to changing current flow
48
Name 2 conditions of resonance
1. Power factor = 1 2. Phase angle = 0
49
Nmae 2 practical applications of resonance
1. Radar recievers 2. Radio recievers
50
In resonance name 3 powers
1. Apparent 2. True 3. Reactive
51
How does a capacitor discharge?
The negative electrons on one plate flow towards the positive plate,acting as a voltage source in the circuit.When the p.d between both plates is 0 the flow stops
52
What is periodic time?
Time it takes to complete one cycle
53
Define frequency of a waveform
Number of cycles completed in 1 second
54
# CCL In an AC inductive circuit current?
Lags V by 90°
55
In a capactive circuit current?
Leads V by 90°

ELECTRICAL ENGINEERING PRINCIPLES LET (1 decks)

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