ch27 - alternating current

Question 1

ac graph is

Answer 1

sinusoidal
. up part positive current
. down part negative current

Question 2

in ac

Answer 2

direction of current reverses every half cycle

Question 3

do ac and shm have same graph

Answer 3

yes

Question 4

sinusoidal

Answer 4

having a magnitude that varies in the form of a sine curve

Question 5

ac graph axis

Answer 5

. x is time
. y is current

Question 6

ac graph equation

Answer 6

I = Io * sin wt

. where Io is peak value of alternating current
. where w is angular frequency of supply

Question 7

alternating current producted in

Answer 7

power stations by large generators

Question 8

generator

Answer 8

coil rotating on magnetic field

Question 9

producing ac (what happens)

Answer 9

. generator is coil rotating in magnetic field
. emf induced in coil according to Faraday’s and Lenz’s laws of em induction
. emf V varies sinusoidally

Question 10

alternating voltage

Answer 10

. sinusoidal
. V = Vo * sin wt

Question 11

oscilloscope used to measure

Answer 11

frequency and voltage of ac

Question 12

types of oscilloscope

Answer 12

cathode ray oscilloscope (CRO)
. electron beam goes through two pairs of parallel plates
. when beam hit screen, spot of light is produced
. x shift and y shift can be controlled
. voltage time graph

digital oscilloscope
. more compact
. stores data
. display traces later

Question 13

is current and voltage are varying all the time

Answer 13

power is always varying too

Question 14

root mean square (rms) value

Answer 14

the rms value of an alternating current is that steady current that delivers the same average power as the ac to a resistive load

Question 15

direct voltage in relation to Vo

Answer 15

about 70% of Vo

Question 16

rms of ac is

Answer 16

steady current that delivers the same average power as the ac to a resistive load

Question 17

rms value

Answer 17

Irms = Io/ root 2
. where Io is peak current

Vrms = Vo/ root 2
where Vo is peak voltage

Question 18

why do we need average power

Answer 18

power contantly varying

Question 19

how to find average power, overall

Answer 19

need to compare ac and dc and find common value where average power is same

Question 20

how to find average power, method

Answer 20

. two filament lamps, one ac one dc
. adjuct ac supply so brightness is equal
. compare output voltages on oscilloscope

Question 21

ac may at times deliever more or less power than dc, but avgrage power is same

Question 22

all power equations

Answer 22

P = I²R
P = IV
P = V²/R

Question 23

for ac peak power is

Answer 23

twice average power

Question 24

explaining rms

Answer 24

<I²> = 0.5Io²
Irms = root <I²> = root 0.5Io²

Io = (root 2) *Irms

Question 25

rectification

Answer 25

process of converting ac to dc

Question 26

rectification methods

Answer 26

. half wave rectification (power is reduced) . bridge rectifier

Question 27

half wave rectification

Answer 27

. ac applied to ciecuit with diode and resistor in series . diode will only conduct during positive cycles . thus there is only current in positive cycles . thus Vout will fluctuate negative cycles look chopped off

Question 28

bridge rectifier

Answer 28

. ac supply to four diodes, to resistor . current in resistor is ALWAYS downwards . if upper power is positive: 2 and 3 diode conduct, are forward bias . if lower power is negative: 1 and 4 diode conduct, are forward bias

Question 29

bridge rectifier graph

Answer 29

constant bumps, full wave rectification

Question 30

recification graph

Answer 30

sinusoidal but negative parts cut off

Question 31

smoothing

Answer 31

producing steady from bumpy dc from recification

Question 33

how to smoothen

Answer 33

. capacitor parallel to a load resistor . capacitor charges up and maintains voltage at high level . capacitor gradually discharges when recified voltage drops, but then rises again

Question 34

more resistance means slower or faster discharge of capacitor

Answer 34

slower

Question 35

more resistance means slower or faster dischs

Question 36

less ripple size in smoothing

Answer 36

. more time constant . more C . more R