bt 224 resistance and capacitive ccts Flashcards

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?

20
Q

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

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
when inductors and capacitors are connected in // their ccts are _________ degrees out of phase
180
26
When a // cct contains both inductive and capacitive loads, each load draws the same _________ as if was alone on the RLC cct
current
27
The ac current that ciculates between the coil and the source __________ 90 degrees. as a result these ccts are ________ degrees out of phase
lags 180 degrees
28
can you connect a coil in series with a capacitor
no
29
When inductive and capacitive current are equal what will happen to the current
all the reactive power will circulate within the cct and there is no reactive demand on the suppy
30
In AC systems how often does the current change directions
every half cycle
31
A capacitive power wave is _______- degrees out of phase with the inductive power wave
180
32
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
returning it
33
What happens when voltage and current are in phase
-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
what happens when the phase angle falls between 0-90 degrees
-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
What does the power wave represent
the rate that energy is delivered through the cct and thr direction the enrgy is moving
36
when a cct contains resistance, inductive and capacitance in // the opposite side of the current trangle is the _________________________
total reactive current
37
What does an impedance triangle do
summarizes the relationships between series resistance and reactance and provides a method for calculating impedance and phase angle
38
Where does the oposition to current come from in a cct
volt drop that is across the loads
39
When 2 or more loads are connected in // across a supply how does each load draw current
independantly
40
when 2 or more loads are connected in series across a supply when will the current rise
-rises until the total volt drop is equal to the applied voltage and 180 degrees out of phase
41
what happens when you connect coils and capacitors in series
its dangerous
42
When inductors and capacitors are connected in // their current are _______ out of phase
180 degrees
43
what is parallel resonance
if the capacitance or inductance can be adjusted, the cct current will be minimum when the 2 reactances are perfectly matched
44
what happens in a cct at parallel reasonance
-supply provides only in-phase resistive current -phase angle is 0 -cct current is at a minimum -impedance is at a maximum
45
What is series reasonance
-if the inductive and capacitive reactances can be adjusted, the current will be at maximum when they are perfectly matched.
46
What happens in a series cct at series reasonance
-impencance is low -current and volt drops are high -phase angle is 0
47