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Level 2 > bt 224 resistance and capacitive ccts > Flashcards

bt 224 resistance and capacitive ccts Flashcards

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1
Q

what do sine wave diagrams do

A

help visulize the relationships between AC voltages and currents

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2
Q

what do phasor diagrams represent

A

quantities and phase relationships

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3
Q

what is one cycle of a sine wave

A

360 degrees

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4
Q

current through a pure inductance _______ rhe voltage across it by 90 degrees in ac ccts

A

lags

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5
Q

current in a capacitance _______ the voltage across it by 90 degrees in ac ccts

A

leads

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6
Q

what is impedance

A

The total opposition to current flow. (Z)

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7
Q

equation for impedance

A

Z= E divided by I

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8
Q

Energy is the ability to ____________

A

do work

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9
Q

What is power

A

The rate at witch energy is transferred from one system to another.

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10
Q

What is the SI unit of energy and power

A

-joules
-watts (joules/second)

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11
Q

In AC systems how often does current change directions

A

every half cycle

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12
Q

How are AC loads classified as and what do they do.

A

-Active loads do real work
-reactive loads store the energy they recieve and return it within the same AC current cycle

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13
Q

What is Active power

A

-called true power
-the rate of net energy transfer through the cct.
-measured in Watts

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14
Q

What is reactive power

A

-rate energy is circulated betweeb the reactive load and the supply
-Measured in VARS
-doesnt do “work” so cant be in watts
-inductive or capacitive

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15
Q

what is apparent power

A

-measured in volt-amps (VA)
-indicates how close a cct is operating capacity without considering how much load is active or reactive.
- = volts x amps

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16
Q

what is power factor. how to calculate

A
  • ratio of active power to apparent power
    -cct capacity being used to do work compared to total cct capacity in use.
  • PF= Watts divided by VA
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17
Q

Define energy and power

A

energy-ablity to do work
power- rate work is being done

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18
Q

What is the SI unit for energy?

A

Joules

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19
Q

What is the SI unit for power?

A

Watts

20
Q

What unit is used for energy by North American electrical suppliers?

A

kW/hr

21
Q

In what basic way is a reactive load different from an active load?

A

circulating energy not doing any actual work

22
Q

Equation for watts

A

W= voltage x IR

23
Q

equation for VARS

A

E x I xl
E x I x sin<0

24
Q

Equations for VA

A

E x It
E x I

25
Q

when inductors and capacitors are connected in // their ccts are _________ degrees out of phase

A

180

26
Q

When a // cct contains both inductive and capacitive loads, each load draws the same _________ as if was alone on the RLC cct

A

current

27
Q

The ac current that ciculates between the coil and the source __________ 90 degrees. as a result these ccts are ________ degrees out of phase

A

lags
180 degrees

28
Q

can you connect a coil in series with a capacitor

A

no

29
Q

When inductive and capacitive current are equal what will happen to the current

A

all the reactive power will circulate within the cct and there is no reactive demand on the suppy

30
Q

In AC systems how often does the current change directions

A

every half cycle

31
Q

A capacitive power wave is _______- degrees out of phase with the inductive power wave

A

180

32
Q

A capacitor that is out of phase with an inductor takes in energy at the exact same time the inductor is ______________ to the cct and vise versa

A

returning it

33
Q

What happens when voltage and current are in phase

A

-power wave is all positive
-All enrgy carries by the cct is used by active power loads
-when the current is 90 degrees out of phase the cct carries the energy that circulates between a reactive load and its source of current

34
Q

what happens when the phase angle falls between 0-90 degrees

A

-positive portion of the power wave is larger then the negative portion
-cct carries active and reactive power
-active power is = to the difference between the positive and negative waves
-the reactive power is the negative side of the wave plus a matching portion of the positive side

35
Q

What does the power wave represent

A

the rate that energy is delivered through the cct and thr direction the enrgy is moving

36
Q

when a cct contains resistance, inductive and capacitance in // the opposite side of the current trangle is the _________________________

A

total reactive current

37
Q

What does an impedance triangle do

A

summarizes the relationships between series resistance and reactance and provides a method for calculating impedance and phase angle

38
Q

Where does the oposition to current come from in a cct

A

volt drop that is across the loads

39
Q

When 2 or more loads are connected in // across a supply how does each load draw current

A

independantly

40
Q

when 2 or more loads are connected in series across a supply when will the current rise

A

-rises until the total volt drop is equal to the applied voltage and 180 degrees out of phase

41
Q

what happens when you connect coils and capacitors in series

A

its dangerous

42
Q

When inductors and capacitors are connected in // their current are _______ out of phase

A

180 degrees

43
Q

what is parallel resonance

A

if the capacitance or inductance can be adjusted, the cct current will be minimum when the 2 reactances are perfectly matched

44
Q

what happens in a cct at parallel reasonance

A

-supply provides only in-phase resistive current
-phase angle is 0
-cct current is at a minimum
-impedance is at a maximum

45
Q

What is series reasonance

A

-if the inductive and capacitive reactances can be adjusted, the current will be at maximum when they are perfectly matched.

46
Q

What happens in a series cct at series reasonance

A

-impencance is low
-current and volt drops are high
-phase angle is 0

47
Q
A

Level 2 (10 decks)

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