Electrical Term 1

Question 1

What is positive power dissipation?

Answer 1

Component that consumes energy eg lightbulb/ areoplane

Question 2

What are independent sources?

Answer 2

Constant supply of voltage/ current

Question 3

What are independent sources represented by?

Answer 3

Cirlces

Question 4

What are dependent sources represented by?

Answer 4

Diamonds

Question 5

What do the first three/ four bands on a resistor tell you?

Answer 5

Numbers for resistance value - last of these bands is the resistance multiplier

Question 6

What is the last band on a resistor tell you?

Answer 6

Tolerance - actual value will vary from nominal - due to manufacturing- represents max deviation

Question 7

How do inductors store energy?

Answer 7

As a magnetic field

Question 8

Forward biaising

Answer 8

Current flowing

Question 9

Reverse biasing

Answer 9

Current restricted

Question 10

Which way does current flow in a resistor?

Answer 10

From triangle base to line

Question 11

What are transistors constructed from?

Answer 11

Semi conductor materials

Question 12

What are the three transistor terminals called?

Answer 12

The collector, The base, the emitter

Question 13

What is a transistor like?

Answer 13

A tap - how much current can flow

Question 14

What is the saturated mode of a transistor?

Answer 14

When it is operated completely on or off

Question 15

What is a node in a circuit?

Answer 15

Where two or more branches connect

Question 16

What is an independent loop?

Answer 16

At least one branch high is not part of another independent loop

Question 17

What is a mesh?

Answer 17

A loop that doesn’t house loops inside of it

Question 18

What is the theorem of network typology?

Answer 18

b= l + n - 1

Question 19

What is an open circuit modelled by?

Answer 19

Very high resistance

Question 20

What resistance is there in a short circuit?

Answer 20

No resistance

Question 21

Why might you use multiple resistors rather than one?

Answer 21

less expensive, lower concentration of dissipated heat,

Question 22

What are planar circuits?

Answer 22

Can be drawn on a flat surface with no branches crossing each other

Question 23

What is superposition in relation to circuits?

Answer 23

Find voltages/ currents as if the sources act alone - then sum these

Question 24

In superposition what is a voltage source replaced with?

Answer 24

Internal resistance modelled as a resistor
(or short circuit if ideal)

Question 25

In superposition what is a current source replaced with?

Answer 25

an open circuit

Question 26

What are the two types of equivalent circuits?

Answer 26

Thenenin and Norton

Question 27

What is in Thevenin’s Equivalent Circuit?

Answer 27

an open circuit voltage and a resistor in series modelling equivalent resistance

Question 28

What is in Norton's equivalent circuit?

Answer 28

a current source and equivalent resistor in parallel

Question 29

What is the goal of impedance matching?

Answer 29

to deliver the maximum power from the cell to the load - has nothing to do with efficiency

Question 30

When is impedance matching generally used?

Answer 30

When the load is a signal rather than power transmission (eg audio engineering)

Question 31

What is the maximum power transfer theorem?

Answer 31

The maximum power is transferred when the load resistance equals the Thevenin or Norton resistance of the power network

Question 32

What two parts of time response for an AC circuit are there?

Answer 32

transient response and steady state response

Question 33

What is an LTI system?

Answer 33

time-invariant, it doesn't matter when the change is applied the output will be the same

Question 34

What two important properties do LTI systems satisfy?

Answer 34

Homogeneity and Superposition

Question 35

What does homogeneity refer to in the context of AC circuits?

Answer 35

if we increase input (eg multiply by a constant) the output will change by the same amount

Question 36

What does superposition refer to in the context of AC circuits?

Answer 36

output = sum of inputs

Question 37

If the input to a LTI system is a sinewave the output will be a sinewave with the same...?

Answer 37

frequency

Question 38

As well as resistance AC circuits have?

Answer 38

Reactance

Question 39

Reactive elements... energy

Answer 39

store and release

Question 40

What is impedance of an AC circuit?

Answer 40

combination of resistance and reactance

Question 41

What is reactance?

Answer 41

A property that opposes a change in current

Question 42

What phase shift between voltage and current occurs when reactance is present?

Answer 42

90 degree

Question 43

With capacitive reactance the current waveform /// the voltage by 90 degrees

Answer 43

leads

Question 44

With inductive reactance the current waveform /// the voltage by 90 degrees

Answer 44

lags

Question 45

How do you work out impedance?

Answer 45

Z=R+j(Xl-Xc)

Question 46

For an impedance with both inductance and capacitance at a low frequency what is the impedance like?

Answer 46

Large and leading as the capacitance term (1/cw) dominates

Question 47

For an impedance with both inductance and capacitance at a high frequency what is the impedance like?

Answer 47

large and lagging (impedance term (Lw) dominates

Question 48

What is the minimum impedance (with both inductance and capacitance)?

Answer 48

R (resistance) and Lw & 1/Cw cancel) - hence the angle is zero

Question 49

What is it called when impedance is a minimum (and equal to R)?

Answer 49

Resonance

Question 50

What is reactive power due to?

Answer 50

Due to the movement of energy within a circuit (between reactive components) - the energy doesnt leave the circuit

Question 51

What is the name of power dissipated by a resistor?

Answer 51

active/real power

Question 52

What is reactive power measured in?

Answer 52

VAr (Volt amperes reactive)

Question 53

The power angle and impedance angle are the same when...

Answer 53

there is a single resistive load - all the components are in series

Question 54

What is the reverse piezo electric effect?

Answer 54

a voltage is applied to a material which produces a force

Question 55

What are some applications of the piezo electric effect?

Answer 55

spark ignitors, microphones

Question 57

What is the difference between a wound field machine and a permanent magnet machine?

Answer 57

The stator has its own coils - you can confíela the strength of the magnetic field

Question 58

What are some disadvantages of a wound field machine compared to a permanent magnet machiene?

Answer 58

Field has to have its own power supply, losses are associated with the resistance of the field coils

Question 59

What two things are used to deal with the fact the armature coils are mounted to a rotating structure?

Answer 59

Commutator and brushes

Question 60

Where does the energy conversion take place in a DC brushed machiene?

Answer 60

In the air gap between the rotor and stator

Question 61

Why would an air gap in a DC brushed machine need to be small?

Answer 61

So it doesn’t effect the amount of magnetic flux ( air has a very low relative permeability)

Question 62

Why would an air gap in a DC brushed machiene need to be large enough?

Answer 62

Accommodates manufacturing tolerances (doesn’t cause the rotor scraping and jamming on the Moro out)

Question 63

What is a positive to cylindrical cells?

Answer 63

robust - able to withstand forces and pressures

Question 64

What are button cells used for?

Answer 64

low power applications

Question 65

What are prismatic cells used for?

Answer 65

custom designed for specific applications to protect against mechanical damage