bt 224 resistance and capacitive ccts

Question 1

what do sine wave diagrams do

Answer 1

help visulize the relationships between AC voltages and currents

Question 2

what do phasor diagrams represent

Answer 2

quantities and phase relationships

Question 3

what is one cycle of a sine wave

Answer 3

360 degrees

Question 4

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

Answer 4

lags

Question 5

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

Answer 5

leads

Question 6

what is impedance

Answer 6

The total opposition to current flow. (Z)

Question 7

equation for impedance

Answer 7

Z= E divided by I

Question 8

Energy is the ability to ____________

Answer 8

do work

Question 9

What is power

Answer 9

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

Question 10

What is the SI unit of energy and power

Answer 10

-joules
-watts (joules/second)

Question 11

In AC systems how often does current change directions

Answer 11

every half cycle

Question 12

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

Answer 12

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

Question 13

What is Active power

Answer 13

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

Question 14

What is reactive power

Answer 14

-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

Question 15

what is apparent power

Answer 15

-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

Question 16

what is power factor. how to calculate

Answer 16

• 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

Question 17

Define energy and power

Answer 17

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

Question 18

What is the SI unit for energy?

Answer 18

Joules

Question 19

What is the SI unit for power?

Answer 19

Watts

Question 20

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

Answer 20

kW/hr

Question 21

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

Answer 21

circulating energy not doing any actual work

Question 22

Equation for watts

Answer 22

W= voltage x IR

Question 23

equation for VARS

Answer 23

E x I xl
E x I x sin<0

Question 24

Equations for VA

Answer 24

E x It
E x I

Question 25

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

Answer 25

180

Question 26

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

Answer 26

current

Question 27

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

Answer 27

lags 180 degrees

Question 28

can you connect a coil in series with a capacitor

Answer 28

no

Question 29

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

Answer 29

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

Question 30

In AC systems how often does the current change directions

Answer 30

every half cycle

Question 31

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

Answer 31

180

Question 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

Answer 32

returning it

Question 33

What happens when voltage and current are in phase

Answer 33

-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

Question 34

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

Answer 34

-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

Question 35

What does the power wave represent

Answer 35

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

Question 36

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

Answer 36

total reactive current

Question 37

What does an impedance triangle do

Answer 37

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

Question 38

Where does the oposition to current come from in a cct

Answer 38

volt drop that is across the loads

Question 39

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

Answer 39

independantly

Question 40

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

Answer 40

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

Question 41

what happens when you connect coils and capacitors in series

Answer 41

its dangerous

Question 42

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

Answer 42

180 degrees

Question 43

what is parallel resonance

Answer 43

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

Question 44

what happens in a cct at parallel reasonance

Answer 44

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

Question 45

What is series reasonance

Answer 45

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

Question 46

What happens in a series cct at series reasonance

Answer 46

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