on tap ltbt chuong ddxc co dap an va huong dan

8/4/2019 On Tap LTBT Chuong DDXC Co Dap an Va Huong Dan

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Trng THPT Ph inn tp LT+BTDng in xoay chiu Gio vin: Trn Thanh Vn

Trang 1

Chng 5 - Dng in xoay chiu

I. H thng kin thc trong chng1) Dng in xoay chiu, cc gi tr hiu dng:

+ Khung dy dn din tch S quay u vi vn tc gc trong t trng u cm ng t B, sao cho trckhung vung gc vi cm ng t B, t thng qua khung bin thin theo nh lut cm ng in t trong khung c

sut in ng cm ng xoay chiu: e =t

= - /(t) = E0 cos(t + 0),

Vi E0 = NBSl bin ca sut in ng.Ni hai u khung vi mch in, trong mch chiu in th: u = U0cos(t + 1).Mch kn, trong mch c cng dng in: i = I0cos(t+ 2).+ Hiu in th bin i iu ho theo thi gian gi l hiu in th xoay chiu. Cng dng in bin

i iu ho theo thi gian gi l cng dng in xoay chiu.

+ Chu k T & tn s f ca dng in xoay chiu:

21

fT ; = 2f l tn s gc ca dng in.

+ Cng hiu dng ca dng in xoay chiu bng cng dng in khng i no , m khi ln lt

cho chng i qua cng mt dy dn trong cng mt thi gian th to ra nhit lng nh nhau. ln: 20

II .

Tng t ta c hiu in th hiu dng v sut in ng hiu dng:2

0UU ;2

0EE

2) Mch xoay chiu ch c in tr thun hoc cun dy thun cm hoc t in:+ Mch xoay chiu ch c in tr thun R: cng dng in v hiu in th cng pha.i = I0cos(t+ ) th u = U0cos(t+ ); U0 = I0.R; U = I.R.+ Mch xoay chiu ch c cun dy thun cm L: cng dng in tr pha /2 so vi hiu in th (hay

hiu in th sm pha /2 so vi cng dng in.

u = U0cos(t + 0) th )tcos(Ii2

00

hay i = I0cos(t + 0) th )tcos(Uu

200

.

U0 = I0.ZL; U = I.ZL. ZL = L..+ Mch xoay chiu ch c t in C: cng dng in sm pha /2 so vi hiu in th (hay hiu in th

tr pha /2 so vi cng dng in.

u = U0cos(t + 0) th )tcos(Ii2

00

hay i = I0cos(t + 0) th )tcos(Uu

200

.

U0 = I0.ZC; U = I.ZL.

C

ZC1

.

3) Mch xoay chiu RLC (ni tip):Hiu in th lch pha so vi cng dng in.i = I0cos(t + 0) th u = U0cos(t + 0 + ). Vi u = uR + uL + uC; U0 = I0.Z, U = I.Z; Z l tng tr ca mch

Z = 22 )( CL ZZR ; U l hiu in th 2 u mch, U = 22 )( CLR UUU ; UR = IR ; UL = IZL ; UC =

IZCl hiu in th hai u R , L , C

tg =0

00

R

CL

R

CLCL

U

UU

U

UU

R

ZZ

, > 0 th u sm pha hn i, < 0 th u tr pha hn i.

Cc trng hp ring:* on mch ch c R: uR & i cng pha* on mch ch c L: uLsm pha /2 so vi i* on mch ch c C: uCtr pha /2 so vi i* on mch ch c L & C: ZL > ZCth u sm pha /2 so vi i; ZL < ZCth u tr pha /2 so vi i* on mch c ZL > ZC, ( UL > UC) hay c tnh cm khng: th > 0

* on mch c ZL < ZC, ( UL < UC ) hay c tnh dung khng: th < 04) Gin vc t : Chn Ox l trc dng in .+ Vi on mch ch c R hoc L hoc C :


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Trang 2

+ Vi on mch RLC ( Mch khng phn nhnh )

UL > UC (hay ZL > ZC) UL < UC (hay ZL < ZC)

5) Mt s trng hp thng gp:+ on mch ch c R & L hay cun dy c in tr thun R & h s t cm L:

Ud = IZd; vi Zd =22

LZR ; hoc Ud =22

LR UU ; tg = ZL/R = UL/UR

+ on mch c R & C: URC= IZ; vi Z =22

CZR ; URC =22

CR UU ; tg = -ZC/R = -UC/UR

+ on mch c L & C: U = IZ; vi Z = ZL - ZC; = /2 khi ZL > ZC ; = - /2 khi ZL < ZC+ Cng hng in: Khi mch RLC c ZL = ZCth cng dng in trong mch cc i.

hay

C

L1

=> LC2= 1 . Ngi ta gi hin tng ny l cng hng in.

Khi Imax = U/R ; U = UR , UL = UC ; = 0 , i & u cng pha ; P = UI = U2/R6) Cng sut ca dng in xoay chiu :

+ Cng sut tiu th on mch: P = UIcos = I2R = U2R/Z = UR I ;

+ H s cng sut :I.U

P

U

U

U

U

Z

Rcos

0

0 .

+ on mch ch c L hoc C hoc c L & C : Cng sut = 0

+ Thng cos < 1. Mun tng h s cng sut ngi ta thng mc thm t in vo mch.+ in nng tiu th on mch : A = Pt7) My pht in xoay chiu mt:

+ Cc my pht in xoay chiu hot ng nh hin tng cm ng in t v u c hai b phn chnh l phn ng v phn cm. Sut in ng ca my pht in c xc nh theo nh lut cm ng in t:

)tcos(EtsinNdt

de

200

; E0 = N0; 0 = BS.

+ Phn sinh ra t trng l phn cm, phn sinh ra dng in l phn ng.+ B phn ng yn l stato, b phn chuyn ng l rto.+ My pht phn cm ng yn (stato), phn ng quay (rto) th ly dng in ra ngoi bng b gp in.

Gm hai vnh khuyn quay cng trc vi khung, mi vnh ni vi mt u khung; hai thanh qut c nh, mithanh t vo mt vnh khuyn; l hai cc ca my.

+ Thng dng nam chm in. Dng in cung cp cho nam chm trch ra mt phn t my.+ Thng my pht in phm cm (nam chm) quay, phn ng (khung dy) ng yn trng phng tia la

in b gp v mn b gp.+ Thn rto v stato c ghp t nhiu l thp mng (chng dng Phu-c), trn c cc rnh dc t cc cun

dy ca phn cm v phn ng.

I ROU x

O I

CU

xL

U

O I x

LU

Ox

CU

CL UU U

RU

Ox

LU

CU

CL UU

RU

U


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Trang 3

+ Tn s dng in: pn

f60

; p l s cp cc ca my pht, n l s vng quay rto mt pht.

8) Dng in xoay chiu ba pha:+ Dng in xoay chiu ba pha l h thng ba dng in xoay chiu mt pha, gy ra bi ba sut in ng

cng tn s, cng bin nhng lch nhau v pha l 2/3 hay thi gian 1/3 chu k..

e1 = E0cost; e2 = E0cos(t - 2/3); e3 = E0cos(t + 2/3).Nu ti ba pha nh nhau th cng dng in trong ba pha cng cng bin nhng lch pha 2 /3 hay120

0.

+ My pht in xoay chiu ba pha: stato c ba cun dy ca phn ng ging nhau v c t lch nhau120

0trn mt vng trn, r to l nam chm in.Kt cu tng t my pht in xoay chiu mt pha.

+ C hai cch mc dng in xoay chiu ba pha l mc hnh sao v tam gic.

- Mc hnh sao: Ud = 3 UP ; Id = IP.

- Mc tam gic: Ud = UP; Id = 3 IP.+ Dng in xoay chiu 3 pha to ra t trng quay bng cch a dng in pha pha vo 3 cun dy t

lch nhau 1200trn vng trn (tng t stato my pht in 3 pha). Thay i chiu quay bng cch thay i v tr 2trong 3 dy dn ni vo my.

9) ng c khng ng b ba pha:+ Nguyn tc hot ng ca ng c khng ng b ba pha da trn hin tng cm ng in t v s dngt trng quay ca dng in xoay chiu 3 pha.

+ Cu to: stato ging ht my pht in xoay chiu 3 pha. Rto kiu lng sc. Thn stato v rto c ghpt nhiu tm thp k thut mng cch in, trn c cc rnh dc t cc cun dy (satto), t cc thanh nhm cakhung dy (rto).

10) My bin th:l thit b lm vic da trn hin tng cm ng in t, dng tng hoc gim hiu inthxoay chiu m khng lm thay i tn s ca n.

Nu in tr ca cc cun dy c th b qua th hiu in th hiu dng hai u mi cun dy t l vi s

vng dy:2

1

2

1

n

n

U

U .

Nu in nng hao ph ca my bin th khng ng k th cng dng in qua mi cun dy t l nghchvi hiu in th hiu dng hai u mi cun:

1

2

1

2

2

1

n

n

U

U

I

I

11) Vn ti in nng i xa:

Cng sut hao ph trn ng dy ti in c in tr R l2

2

)cosU(

PRP

,

Trong U l hiu in thv P l cng sut truyn i trm pht in, R l in tr ng dy. gim in nng hao ph, cch 1: ngi ta tng U (U tng n ln, hao ph gin n 2ln) dng my bin th lm

tng hiu in th trc khi truyn ti v my bin th l gim hiu in th ni tiu th ti gi tr cn thit. Cch 2: gim in tr ng dy, thng dng cho mch in h th (ti tng cn h).

II. Cu hi v bi tpCh 1: i cng v dng in xoay chiu. Mch xoay chiu ch cha in tr thun

5.1. Chn cu ng. Dng in xoay chiu l dng in:A. c cng bin thin tun hon theo thi gian.B. c cng bin i iu ho theo thi gian.C. c chiu bin i theo thi gian.D. c chu k khng i.

5.2.Chn cu ng. Cc gi tr hiu dng ca dng in xoay chiu:A. c xy dng da trn tc dng nhit ca dng in.B. c o bng ampe k nhit.

C. bng gi tr trung bnh chia cho 2 .

D. bng gi tr cc i chia cho 2.5.3.i vi dng in xoay chiu cch pht biu no sau y l ng?

A. Trong cng nghip, c th dng dng in xoay chiu m in.B. in lng chuyn qua mt tit din thng dy dn trong mt chu k bng khng.C. in lng chuyn qua mt tit din thng dy dn trong khong thi gian bt k u bng khng.


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Trang 4

D. Cng sut to nhit tc thi c gi tr cc i bng 2 ln cng sut to nhit trung bnh.

5.4.Cng dng in trong mch khng phn nhnh c dng i = 2 2 cos100t(A). Cng dng in hiudng trong mch l

A. I = 4A. B. I = 2,83A. C. I = 2A. D. I = 1,41A.

5.5.Hiu in th gia hai u on mch c dng u = 141cos(100t)V. Hiu in th hiu dng gia hai u

on mch lA. U = 141V. B. U = 50Hz. C. U = 100V. D. U = 200V.5.6.Trong cc i lng c trng cho dng in xoay chiu sau y, i lng no c dng gi tr hiu dng?

A. Hiu in th . B. Chu k. C. Tn s. D. Cng sut.5.7.Trong cc i lng c trng cho dng in xoay chiu sau y, i lng no khng dng gi tr hiu

dng?A. Hiu in th . B. Cng dng in. C. Sut in ng. D. Cng sut.

5.8.Pht biu no sau y l khngng?A. Hiu in th bin i iu ho theo thi gian gi l hiu in th xoay chiu.B. Dng in c cng bin i iu hotheo thi gian gi l dng in xoay chiu.C. Sut in ng bin i iu ho theo thi gian gi l sut in ng xoay chiu.D. Cho dng in mt chiu v dng in xoay chiu ln lt i qua cng mt in tr th chng to ra nhit

lng nh nhau.5.9.Mt mng in xoay chiu 220V 50Hz, khi chn pha ban u ca hiu in th bng khng th biu thc

ca hiu in th c dng:A. u = 220cos50t(V). B. u = 220cos50t(V).

C. u = 220 2 cos100t(V). D. u = 220 2 cos100t(V).5.10Mt dng in xoay chiu chy qua in tr R = 10, nhit lng to ra trong 30min l 900kJ. Cng

dng in cc i trong mch lA. I0 = 0,22A. B. I0 = 0,32A. C. I0 = 7,07A. D. I0 = 10,0A.

5.11.Mt chic n nn t di mt hiu in th xoay chiu 119V 50Hz. N ch sng ln khi hiu in thtc thi gia hai u bng n ln hn 84V. Thi gian bng n sng trong mt chu k l bao nhiu?

A. t = 0,0100s. B. t = 0,0133s. C. t = 0,0200s. D. t = 0,0233s.

Ch 2: Dng in xoay chiu trong on mch ch cha cun cm hoc t in5.12.Chn cu ng.

A. T in cho c dng in xoay chiu v dng in mt chiu i qua.B. hiu in th gia hai bn t bin thin sm pha /2 i vi dng in.C. Cng hiu dng ca dng in xoay chiu qua t in t l nghch vi tn s dng in.D. Dung khng ca t in t l nghch vi chu k ca dng in xoay chiu.

5.13.Chn cu ng. tng dung khng ca t in phng c cht in mi l khng kh ta phi:A. tng tn s ca hiu in th t vo hai bn t in.B. tng khong cch gia hai bn t in.C. Gim hiu in th hiu dng gia hai bn t in.D. a thm bn in mi vo trong lng t in.

5.14.Pht biu no sau y ngi vi cun cm?A. Cun cm c tc dng cn tr dng in xoay chiu, khng c tc dng cn tr dng in mt chiu.B. Hiu in th gia hai u cun thun cm v cng dng in qua n c th ng thi bng mt na

cc bin tng ng ca n.C. Cm khng ca cun cm tl nghch vi chu k ca dng in xoay chiu.D. Cng dng in qua cun cm t l vi tn s dng in.

5.15.dng in xoay chiu qua on mch ch c cun cm hay t in hay cun cm ging nhau im no?A. u bin thin tr pha /2 i vi hiu in th hai u on mch.B. u c cng hiu dng t l vi hiu in th hiu dng hai u on mch.C. u c cng hiu dng tng khi tn s dng in tng.D. u c cng hiu dng gim khi tn s im in tng.

5.16.Pht biu no sau y l ngvi mch in xoay chiu ch cha cun cm?

A. Dng in sm pha hn hiu in th mt gc /2.B. Dng in sm pha hn hiu in th mt gc /4.C. Dng in tr pha hn hiu in th mt gc /2.D. Dng in tr pha hn hiu in th mt gc /4.

5.17.Pht biu no sau y l ngvi mch in xoay chiu ch cha t in?


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A. Dng in sm pha hn hiu in th mt gc /2.B. Dng in sm pha hn hiu in th mt gc /4.C. Dng in tr pha hn hiu in th mt gc /2.D. Dng in tr pha hn hiu in th mt gc /4.

5.18.Cng thc xc nh dung khng ca t in C i vi tn s f l

A. fC2ZC B. fCZC C. fC2

1

ZC D. fC

1

ZC

5.19.Cng thc xc nh cm khng ca cun cm L i vi tn s f l

A. fL2ZL B. fLZL C.fL2

1ZL

D.

fL

1ZL

5.20.Khi tn s dng in xoay chiu chy qua on mch ch cha t in tng ln 4 ln th dung khng ca tin

A. tng ln 2 ln. B. tng ln 4 ln. C. gim i 2 ln. D. gim i 4 ln.5.21.Khi tn s dng in xoay chiu chy qua on mch ch cha cun cm tng ln 4 ln th cm khng ca

cun cmA. tng ln 2 ln. B. tng ln 4 ln. C. gim i 2 ln. D. gim i 4 ln.

5.22.Cch pht biu no sau y l khngng?

A. Trong on mch ch cha t in, dng in bin thin sm pha /2 so vi hiu in th.B. Trong on mch ch cha t in, dng in bin thin chm pha /2 so vi hiuin th.C. Trong on mch ch cha cun cm, dng in bin thin chm pha /2 so vi hiu in th.D. Trong on mch ch cha cun cm, hiu in th bin thin sm pha /2 so vi dng in trong mch.

5.23.t vo hai u t in )(104

FC

mt hiu in th xoay chiu tn s 100Hz, dung khng ca t in

l

A. ZC= 200. B. ZC= 100. C. ZC= 50. D. ZC= 25.5.24.t vo hai u cun cm L = 1/(H) mt hiu in th xoay chiu 220V 50Hz. Cng dng in

hiu dng qua cun cm lA. I = 2,2A. B. I = 2,0A. C. I = 1,6A. D. I = 1,1A.

5.25t vo hai u t in )(10 4

FC

mt hiu in th xoay chiu u = 141cos(100t)V. Dung khng ca

t in lA. ZC= 50. B. ZC= 0,01. C. ZC = 1A. D. ZC= 100.

5.26.t vo hai u cun cm )(1HL

mt hiu in th xoay chiu u = 141cos(100t)V. Cm khng ca

cun cm lA. ZL= 200. B. ZL= 100. C. ZL= 50. D. ZL= 25.

5.27.t vo hai u t in )(104

FC

mt hiu in th xoay chiu u = 141cos(100t)V. Cng dng

in qua t in lA. I = 1,41A. B. I = 1,00A. C. I = 2,00A. D. I = 100.

5.28.t vo hai u cun cm )(1HL

mt hiu in th xoay chiu u = 141cos(100t)V. Cng dng

in hiudng qua cun cm lA. I = 1,41A. B. I = 1,00A. C. I = 2,00A. D. I = 100.

Ch 3: Dng in xoay chiu trong on mch khng phn nhnh.5.29.Biu thc hiu in th gia hai u mt on mch v dng qua n l: u = U0sin100t v

i = I0sin(100t +/3). thi im hiu in th c gi tr l u ghi ct bn tri th cng dng in l ic ghi ct bn phi. Hy ghp cc ni dung tng ng ca hai ct vi nhau:

1. u = 02. u = 0,5U0.

3. u = U0.

4. u = 0,5U0 3 .5. u = - 0,5U0.

a) i = I0.b) i = 0,5I0.

c) i = 0,5 3 I0.

d) i = 0.


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5.30.Ngi ta dng cc linh kin gm: in tr thun R, t in C, cun thun cm L ghp ni tip thnh ccmch khc nhau. Cho bit cm khng ca cun dy ZL= 2R, ca t in ZC= R. Hy ghp s cc on mch ct

bn phi vi cc ch ct bn tri tng ng vi n.1. on mch gm R v C.

2. on mch gm R v L.

3. on mch gm L v C.

4. on mch gm R, L v C.

a) Dng in sm pha /2 i vi hiu in th, tng tr bng R 3 b) Dng in tr pha /2 i vi hiu in th, tng tr bng R

c) Dng in sm pha /4 i vi hiu in th, tng tr bng R 2 d) Dng in tr pha /4 i vi hiu in th, tng tr bng R 2 e) Dng in sm pha i vi hiu in th mt gc ln hn /4 tng tr

bng R 5 5.31.Cng hiu dng ca dng in chy trn on mch RLC ni tip khng c tnh cht no di y?

A. Khng ph thuc vo chu k dng in.B. T l thun vi hiu in th hai u on mch.C. Ph thuc vo tn s im in.D. T l nghch vi tng tr ca on mch.

5.32.Dung khng ca mt on mch RLC ni tip c gi tr nh hn cm khng. Ta lm thau i ch mt trongcc thng s ca on mch bng cch nu sau y. Cch no c th lm cho hin tng cng hng in xy ra?

A. Tng in dung ca t in. B. Tng h s t cm ca cun dy.C. Gim in tr ca on mch. D. Gim tn s dng in.5.33. Trong cc cu no di y, cu no ng, cu no Sai? Bit hiu in th gia hai u on mch lc ni

tip sm pha /4 i vi dng in ca n.A. Tn s dng in trong on mch nh hn gi tr cn xy ra cng hng. SaiB. Tng tr ca mch bng hai ln in tr R ca on mch. SaiC. Hiu s gia cm khng v dung khng bng in tr thun ca on mch. ngD. hiu in th hiu dng gia hai u on mch ln hn hiu in th hiu dng gia hai u in tr

2 ln. ngE. Hiu in th gia hai u in tr sm pha /4 i vi hiu in th gia hai bn t. Sai

5.34.Cho on mch nh hnh v. Hiu in th hiu dng

gia hai u cun dy, gia hai bn t, gia hai u onmch ln lt l: UL, UC, U. Bit UL = UC; U = UC .A. V UL UC nn ZL ZC, vy trong mch khng xy ra cng hng.B. Cun dy c in tr thun ng k. Trong mch khng xy ra hin tng cng hng.C. Cun dy c in tr thun ng k. Trong mch xy ra hin tng cng hng.D. Cun dy c in tr thunkhng ng k.

5.35.Mt in tr thun R mc vo mch in xoay chiu tn s 50Hz, mun dng in trong mch sm phahn hiu in th gia hai u on mch mt gc /2

A. ngi ta phi mc thm vo mch mt t in ni tip vi in tr.B. ngi ta phi mc thm vo mch mt cun cm ni tip vi in tr.C. ngi ta phi thay in tr ni trn bng mt t in.D. ngi ta phi thay in tr ni trn bng mt cun cm.

5.36.Cn ghp mt t in ni tip vi cc linh kin khc theo cch no di y, c c on mch xoaychiu m dng in tr pha /4 i vi hiu in th hai u on mch? Bit t in trong mch ny c dungkhng bng 20.

A. Mt cun thun cm c cm khng bng 20.B. Mt in tr thun c ln bng 20.C. Mt in tr thun c ln bng 40v mt cun thun cm c cm khng 20.D. Mt in tr thun c ln bng 20v mt cun thun cm c cm khng 40.

5.37.Mt on mch khng phn nhnh c dng in sm pha hn hiu in th.A. Trong on mch khng th c cun cm, nhng c t in.B. H s cng sut ca on mch c gi tr khc khng.C. Nu tng tn s dng in ln th lch pha gia dng in v hiu in th gim.

D. Nu gim tn s ca dng in th cng hiu dng gim.5.38.on mch RLC ni tip ang xy ra cng hng. Tng dn tn s ca dng in v gi nguyn cc thngs khc ca mch, kt lun no di y khng ng?

A. Cng dng in gim, cm khng ca cung dy tng, hiu in th trn cun dy khng i.B. Cm khng ca cun dytng, hiu in th trn cun dy thay i.

L C


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C. Hiu in th trn t gim.D. Hiu in th trn in tr gim.

5.39.Trong mch RLC mc ni tip, lch pha gia dng in v hiu in th gia hai u on mch phthuc vo

A. cng dng in hiu dng trong mch.B. hiu in th hiu dng gia hai u on mch.

C. cch chn gc tnh thi gian.D. tnh cht ca mch in.

5.40.Pht biu no sau y l khngng?Trong mch in xoay chiu khng phn nhnh khi in dung ca t in thay i v tho mn iu kin

LC

1 th

A. cng dao ng cng pha vi hiu in th gia hai u on mch.B. cng dng in hiu dng trong mch t cc i.C. cng sut tiu th trung bnh trong mch t cc i.D. hiu in th hiu dnggia hai u t in t cc i.

5.41.Pht biu no sau y l khngng?

Trong mch in xoay chiu khng phn nhnh khi in dung ca t in thay i v tho mn iu kin

C

1L

th

A. hiu in th hiu dng gia hai u cun cm t cc i.B. hiu in th hiu dng gia hai u t in v cun cm bng nhau.C. tng tr ca mch t gi tr ln nht.D. hiu in th hiu dng gia hai u in tr t cc i.

5.42.Trong on mch RLC, mc ni tip ang xy ra hin tng cnghng. Tng dn tn s dng in vgia nguyn cc thng s ca mch, kt lun no sau y l khngng?

A. H s cng sut ca on mch gim.B. Cng hiu dng ca dng in gim.C. Hiu in th hiu dng trn t in tng.D. Hiu in th hiudng trn in tr gim.

5.43.Pht biu no sau y l khngng? Trong mch in xoay chiu khng phn nhnh ta c th to ra hiuin th hiu dng gia hai u:

A. cun cm ln hn hiu in th hiu dng gia hai u on mch.B. t in ln hn hiu in th hiu dng gia hai u on mch.C. in tr ln hn hiu in th hiu dng gia hai u on mch.D. t in bng hiu in th hiu dng gia hai u cun cm.

5.44.Cng tc tnh tng tr ca on mch RLC mc ni tip l

A.22)(

CLZZRZ B.

22)(

CLZZRZ

C.22)(

CLZZRZ D.

CLZZRZ

5.45.Dng in chy qua on mch xoay chiu c dng i = 2cos100t(A), hiu in th gia hai u on mchc gi tr hiu dng l 12V, v sm pha /3 so vi dng in. Biu thc ca hiu in th gia hai u on mchl:

A. u = 12cos100t(V). B. u = 12 2 cos100t(V).

C. u = 12 2 cos(100t /3)(V). D. u = 12 2 cos(100t + /3)(V).5.46. Hy chn phng n tr li ng nht.

Dng in xoay chiu qua in tr thun bin thin iu ho cng pha vi hiu in th gia hai u in trA. trong trng hp mch RLC xy ra cng hng in.B. trong trng hp mch ch cha in tr thun R.C. trong trng hp mch RLC khng xy ra cng hng in.D. trong mi trng hp.

5.47.Mch in xoay chiu gm RLC mc ni tip, c R = 30, ZC= 20, ZL= 60. Tng tr ca mch lA. Z = 50. B. Z = 70. C. Z = 110. D. Z = 2500.


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5.48. Cho on mch xoay chiu AB gm in tr R = 100, t in )(104

FC

v cun cm

)(2HL

mc ni tip. t vo hai u on mch mt hiu in th xoay chiu c dng u = 200cos100t(V).

Cng dng in hiu dng trong mch l

A. I = 2A. B. I = 1,4A. C. I = 1A. D. I = 0,5A.

5.49. Cho on mch xoay chiu AB gm in tr R = 60, t in )(104

FC

v cun cm

)(2,0HL

mc ni tip. t vo hai u on mch mt hiu in th xoay chiu c dng

u = 50 2 cos100t(V). Cng dng in hiu dng trong mch lA. I = 0,25A. B. I = 0,50A. C. I = 0,71A. D. I = 1,00A.

Ch 4: Cng sut ca dng in xoay chiu.5.52.Chn cu ng. Cng sut ca dng in xoay chiu trn mt on mch RLC ni tip nh hn tch UI l

do: A. mt phn in nng tiu th trong t in.B. trong cun dy c dng in cm ng.C. hiu in th gia hai u on mch v cng dng in lch pha khng i vi nhau.D. C hin tng cng hng in trn on mch.

5.53. Cng sut ca dng in xoay chiu trn on mch RLC ni tip khng ph thuc vo i lng no sauy?

A. Cng hiu dng ca dng in qua mch.B. Hiu in th hiu dng gia hai u on mch.C. lch pha gia dng in vhiu in th gia hai bn t.D. T s gia in tr thun v tng tr ca mch.

5.54.Chn cu ng. Trn mt on mch xoay chiu, h s cng sut bng 0 (cos = 0), khi:

A. on mch ch cha in tr thun.B. on mch c in tr bng khng.C. on mch khng c t in.D. on mch khng c cun cm.

5.55.Cng sut ca mt on mch xoay chiu c tnh bng cng thc no di y:A. P = U.I; B. P = Z.I

2; C. P = Z.I

2cos; D. P = R.I.cos.

5.56.Cu no di y khng ng?

A. Cng thc tnhZ

Rcos = c th p dng cho mi on mch in.

B. Khng th cn c vo h s cng sut xc nh lch pha gia hiu in th v cng dng in.C. Cun cm c th c h s cng sut khc khng.

D. H s cng sut ph thuc vo hiu in th xoay chiu hai u mch.5.57.Cng sut to nhit trung bnh ca dng in xoay chiu c tnh theo cng thc no sau y?A. P = u.i.cos. B. P = u.i.sin. C. P = U.I.cos. D. P = U.I.sin.

5.58.Pht biu no sau y l khngng?A. Cng sut ca dng in xoay chiu ph thuc vo cng dng in hiu dng trong mch.B. Cng sut ca dng in xoay chiu ph thuc vo hiu in th hiu dng gia hai u on mch.C. Cng sut ca dng in xoay chiu ph thuc vo bn cht ca mch in v tn s dng in trong

mch.D. Cng sut ca dng in xoay chiu ph thuc vo cng sut hao ph trn ng dy ti in.

5.59.i lng no sau y c gi l h s cng sut ca mch in xoay chiu?A. k = sin. B. k = cos. C. k = tan. D. k = cotan.

5.60.Mch in no sau y c h s cng sut ln nht?

A. in tr thun R1ni tip vi in tr thun R2.B. in tr thun R ni tip vi cun cm L.C. in tr thun R ni tip vi t in C.D. Cun cm L ni tip vi t in C.

5.61.Mch in no sau y c h s cng sut nh nht?


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Trang 9

A. in tr thun R1ni tip vi in tr thun R2.B. in tr thun R ni tip vi cun cm L.C. in tr thun R ni tip vi t in C.D. Cun cm L ni tip vi t in C.

5.62.Mch in xoay chiu RLC mc ni tip ang c tnh cm khng, khi tng tn s ca dng in xoay chiuth h s cng sut ca mch

A. khng thay i. B. tng. C. gim. D. bng 1.5.63.Mch in xoay chiu RLC mc ni tip ang c tnh dung khng, khi tng tn s ca dng in xoay

chiu th h s cng sut ca mchA. khng thay i. B. tng. C. gim. D. bng 0.

5.64.Mt t in c in dung C = 5,3F mc ni tip vi in tr R = 300 thnh mt on mch. Mc onmch ny vo mng in xoay chiu 220V 50Hz. H s cng sut ca mch l

A. 0,3331 B. 0,4469 C. 0,4995 D. 0,6662

5.65.Mt t in c in dung C = 5,3F mc ni tip vi in tr R = 300 thnh mt on mch. Mc onmch ny vo mng in xoay chiu 220V 50Hz. in nng m on mch tiu th trong mt pht l

A. 32,22J. B. 1047J. C. 1933J. D. 2148J.

5.66.Mt cun dy khi mc vo hiu in th xoay chiu 50V 50Hz th cng dng in qua cun dy l0,2A v cng sut tiu th trn cun dy l 1,5W. H s cng sut ca mch l bao nhiu?

A. k = 0,15. B. k = 0,25. C. k = 0,50. D. k = 0,75.

Ch 5: My pht in xoay.5.67.Chn cu ng. Trong cc my pht in xoay chiu mt pha:

A. phn to ra t trng l rto.B. phn to ra sut in ng cm ng l stato.C. B gp in c ni vi hai u ca cun dy stato.D. sut in ng ca my t l vi tc quay ca rto.

5.68.Pht biu no sau y ngi vi my pht in xoay chiu?A. Bin casut in ng t l vi s cp ca nam chm.B. Tn s ca sut in ng t l vi s vng dy ca phn ng.C. Dng in cm ng ch xut hin cc cun dy ca phn ng.D. C nng cung cp cho my c bin i hon ton thnh in nng.

5.69. My pht in xoay chiu mt pha v ba pha ging nhau im no?A. u c phn ng quang, phn cm c nh.B. u c b gp in dn in ra mch ngoi.C. u c nguyn tc hot ng da trn hin tng cm ng in t.D. Trong mi vng dy ca rto, sut in ng ca my u bin thin tun hon hai ln.

5.70.Nguyn tc hot ng ca my pht in xoay chiu mt pha da voA. hin tng t cm.B. hin tng cm ng in t.C. khung dy quay trong in trng.D. khung dy chuyn ng trong ttrng.

5.71.Hin nay vi cc my pht in cng sut ln ngi ta thng dng cch no sau y to ra dng inxoay chiu mt pha?A. Nam chm vnh cu ng yn, cun dy chuyn ng tnh tin so vi nam chm.B. Nam chm vnh cu ng yn, cun dychuyn ng quay trong lng nam chm.C. Cun dy ng yn, nam chm vnh cu chuyn ng tnh tin so vi cun dy.D. Cun dy ng yn, nam chm vnh cu chuyn ng quay trong lng stato c cun cc cun dy.

5.72.Pht biu no sau y ngi vi my pht in xoay chiu mt pha?A. Dng in cm ng ch xut hin cc cun dy ca phn ng.B. Tn s ca sut in ng t l vi s vng dy ca phn ng.C. Bin ca sut in ng t l vi s cp cc t ca phn cm.D. C nng cung cp cho my c bin i tun hon thnh in nng.

5.73.Rto ca my pht in xoay chiu l mt nam chm c 3 cp cc t, quay vi tc 1200vng/min. Tn

s ca sut in ng do my to ra l bao nhiu?A. f = 40Hz. B. f = 50Hz. C. f = 60Hz. D. f = 70Hz.

5.74.Phn ng ca mt my pht in xoay chiu c 200vng dy ging nhau. T thng qua mt vng dy cgi tr cc i l 2mWb v bin thin iu ho vi tn s 50Hz. Sut in ng ca my c gi tr hiu dng l baonhiu?


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Trang 10

A. E = 88858V. B. E = 88,858V. C. E = 12566V. D. E = 125,66V.

5.75.Mt my pht in xoay chiu 1 pha c rto gm 4 cp cc t, mun tn s dng in xoay chiu m mypht ra l 50Hz th rto phi quay vi tc l bao nhiu?

A. 3000vng/pht. B. 1500vng/pht.

C. 750vng/pht. D. 500vng/pht

5.76.Mt my pht in m phn cm gm hai cp cc t quay vi tc 1500vng/pht v phn ng gm hai

cun dy mc ni tip, c sut in ng hiu dng 220V, t thng cc i qua mi vng dy l 5mWb. Mi cundy gm c bao nhiu vng?

A. 198 vng. B. 99 vng. C. 140 vng. D. 70 vng.

5.77.Chn cu ng:A. Dng in xoay chiu mt pha ch c th do my pht in xoay chiu mt pha to ra.B. Sut in ng ca my pht in xoay chiu t l vi s vng dy ca phn ng.C. Dng in do my pht in xoay chiu to ra lun c tn s bng s vng quay ca rto.D. Ch c dng xoay chiu ba pha mi to ra t trng quay.

5.78.Dng in xoay chiu ba pha l h thng ba dng in xoay chiu mt pha gy ra bi ba sut in n g cc im no sau y?

A. Cng tn s. B. Cng bin .C. Lch pha nhau 1200. D. C ba c im trn.

5.79.Trong cch mc dng in xoay chiu ba pha i xng theo hnh sao, pht biu no sau y l khngng?

A. Dng in trong dy trung ho bng khng.B. Dng in trong mi pha bng dao ng trong mi dy pha.

C. Hiu in th pha bng 3 ln hiu in th gia hai dy pha.D. Truyn ti in nng bng 4 dy dn, dy trung ho c tit din nh nht.

5.80.Trong cch mc dng in xoay chiu ba pha i xng theo hnh tam gic, pht biu no sau y l khngng?

A. Dng in trong mi pha bng dng in trong mi dy pha.B. Hiu in th gia hai u mt pha bng hiu in th gia hai dy pha.C. Cng sut tiu th trn mi pha u bng nhau.

D. Cng sut ca ba pha bng ba ln cng sut mi pha.5.81.Khi truyn ti in nng ca dng in xoay chiu ba pha i xa ta phi dng t nht l bao nhiu dy dn? A. Hai dy dn. B. Ba dy dn. C. Bn dy dn. D. Su dy dn.

5.82.Hiu in th hiu dng gia hai u mt pha ca mt my pht in xoay chiu ba pha l 220V. Trongcch mc hnh sao, hiu in th hiu dng gia hai dy pha l

A. 220V. B. 311V. C. 381V. D. 660V.

5.83.Cng dng in hiu dng trong mt pha ca my pht in xoay chiu ba pha l 10A. Trong cchmc hnh tam gic, cng dng in trong mi dy pha l

A. 10,0A. B. 14,1A. C. 17,3A. D. 30,0A.

5.84.Mt ng c khng ng b ba pha hot ng bnh thng khi hiu in th hiu dng gia hai u micun dy l 220V. Trong khi ch c mt mng in xoay chiu ba pha do mt my pht ba pha to ra, sut inng hiu dng mi pha l 127V. ng c hot ng bnh thng th ta phi mc theo cch no sau y?

A. Ba cun dy ca my pht theo hnh tam gic, ba cun dy ca ng c theo hnh sao.B. Ba cun dy ca my pht theo hnh tam gic, ba cun dy ca ng c theo tam gic. C. Ba cun dy ca my pht theo hnh sao, ba cun dy ca ng c theo hnh sao.D. Ba cun dy ca my pht theo hnh sao, ba cun dy ca ng c theo hnh tam gic.

Ch 6: ng c khng ng b 3 pha.5.85.Chn cu ng.

A. Ch c dng in ba pha mi to ra t trng quay.B. Rto ca ng c khng ng b ba pha quay vi tc gc ca t trng.C. T trng quay lun thay i c hng v tr s.D. Tc gc ca ng c khng ng b ph thuc vo tc quay ca t trng v momen cn.

5.86.Pht biu no sau y v ng c khng ng b ba pha l sai?A. Hai b phn chnh ca ng c l rto v stato.B. B phn to ra t trng quay l stto.C. Nguyn tc hot ng ca ng c l da trn hin tng in t.


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D. C th ch to ng c khng ng b ba pha vi cng sut ln.5.87.u im ca ng c khng ng b ba pha so va ng c in mt chiu l g?

A. C tc quay khng ph thuc vo ti.B. C hiu sut cao hn.C. C chiu quay khng ph thuc vo tn s dng in.

D. C kh nng bin in nng thnh c nng.5.88.Mt ng c khng ng b ba pha hot ng bnh thng khi hiu in th hiu dng gia hai u mi

cun dy l 100V. Trong khi ch c mt mng in xoay chiu ba pha do mt my pht ba pha to ra, sut inng hiu dng mi pha l 173V. ng c hot ng bnh thng th ta phi mc theo cch no sau y?

A. Ba cun dy ca my pht theo hnh tam gic, ba cun dy ca ng c theo hnh sao.B. Ba cun dy ca my pht theo hnh tam gic, ba cun dy ca ng c theo tam gic. C. Ba cun dy ca my pht theo hnh sao, ba cun dy ca ng c theo hnh sao.D. Ba cun dy ca my pht theo hnh sao, ba cun dy ca ng c theo hnh tam gic.

5.89.Pht biu no sau y l ng? Ngi ta c th to ra t trng quay bng cch choA. nam chm vnh cu hnh ch U quay u quanh trc i xng ca n.B. dng inxoay chiu chy qua nam chm in.C. dng in xoay chiu mt pha chy qua ba cun dy ca stato ca ng c khng ng b ba pha.D. dng in mt chiu chy qua nam chm in.

5.90.Pht biu no sau y l ng? Ngi ta c th to ra t trng quay bng cch cho dng in:A. xoay chiu chy qua nam chm in.B. mt chiu chy qua nam chm in.C. dng in xoay chiu mt pha chy qua ba cun dy ca stato ca ng c khng ng b ba pha.D. dng in xoay chiu ba pha chy qua ba cun dy ca stato ca ng c khng ng b ba pha.

5.91.Pht biu no sau y l khngng? Cm ng t do c ba cun dy gy ra ti tm stato ca ng ckhng ng b ba pha, khi c dng in xoay chiu ba pha i vo ng c c:

A. ln khng i.B. phng khng i.C. hng quay u.

D. tn s quay bng tn s dng in.5.92.Gi B0l cm ng t cc i ca mt trong ba cun dy ng c khng ng b ba pha khi c dng invo ng c. Cm ng t do c ba cun dy gy ra ti tm stato c gi tr

A. B = 0. B. B = B0. C. B = 1,5B0. D. B = 3B0.

5.93.Stato ca mt ng c khng ng b ba pha gm 6 cun dy, cho dng in xoay chiu ba pha tn s50Hz vo ng c. T trng ti tm ca stato quay vi tc bng bao nhiu?

A. 3000vng/min. B. 1500vng/min. C. 1000vng/min. D. 500vng/min.

5.94.Stato ca mt ng c khng ng b ba pha gm 9 cun dy, cho dng in xoay chiu ba pha tn s50Hz vo ng c. Rto lng sc ca ng c c th quay vi tc no sau y?

A. 3000vng/min. B. 1500vng/min. C. 1000vng/min. D. 900 vng/min.

5.95.Pht biu no sau y l ng? Nguyn tc hot ng ca ng c khng ng b ba pha da trn hintng:

A. cm ng in t.B. t cm.C. cm ng in t v lc t tc dng ln dng in.D. t cm v lc t tc dng ln dng in.

5.96.Pht biu no sau y l ng?A. Dng in xoay chiu mt pha ch c th do my pht in xoay chiu mt pha to ra.B. Sut in ng ca my pht in xoay chiu t l vi s vng quay trong mt pht ca r to.C. Dng in do my pht in xoay chiu to ra lun c tn s bng tn s quay ca r to.D. Ch c dng in xoay chiu ba pha mi to ra t trng quay.

5.97.Thit b no sau y c tnh thun nghch?A. ng c khng ng b ba pha.B. ng c khng ng b mt pha.

C. My pht in xoay chiu mt pha.D. My pht in mt chiu.

Ch 7: My bin p. Truyn ti in.5.98.Cu no sau y l ngkhi ni v my bin th?


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A. My bin p ch cho php bin i hiu in th xoay chiu.B. Cc cun dy my bin p uc cun trn li st.C. Dng in chy trn cc cun dy s cp v th cp khc nhau v cng v tn s.D. Sut in ng trong cc cun dy ca my bin p u l sut in ng cm ng.

5.99.Chn cu ng. Mt my bin p c cun th cp mc vi in tr thun, cun s cp ni vi ngun inxoay chiu. in tr cc cun dy v hao ph in nng my khng ng k. Nu tng tr s in tr mc vi cun

th cp ln hai ln th:A. Cng hiu dng ca dng in chy trong cun th cp gim hai ln, trong cun s cp khng i.B. hiu in th hai u cun s cp v th cp u tng ln hai ln.C. sut in ng cm ng trong cun dy th cp tng ln hai ln, trong cun s cp khng i.D. cng sut tiu th mch s cp v th cp u gim hai ln.

5.100.Chn cu Sai. Trong qu trnh ti in nng i xa, cng sut hao ph:A. t l vi thi gian truyn ti.B. t l vi chiu di ng dy ti in.C. t l nghch vi bnh phng hiu in th gia hai u dy trm pht in.D. t l vi bnh phng cng sut truyn i.

5.101.Bin php no sau y khnggp phn tng hiu sut ca my bin th?A. Dng dy dn c in tr sut nh lm dy cun bin th.

B. Dng li st c in tr sut nh.C. Dng li st gm nhiu l mng ghp cch in vi nhau.D. t cc l thp song song vi mt phng cha cc ng sc t.

5.102.Nhn xt no sau y v my bin th l khngng?A. My bin th c th tng hiu in th.B. My bin th c th gim hiu in th.C. My bin th c ththay i tn s dng in xoay chiu.D. My bin th c tc dng bin i cng dng in.

5.103.Hin nay ngi ta thng dng cch no sau y lm gim hao ph in nng trong qu trnh truyn tii xa?

A. Tng tit din dy dn dng truyn ti.B. Xy dng nh my in gn ni tiu th.C. Dng dy dn bng vt liu siu dn.D. Tng hiu in th trc khi truyn ti in nng i xa.

5.104.Phng php lm gim hao ph in nng trong my bin th lA. my bin th ni kh thong.B. li ca my bin th c cu to bng mt khi thp c.C. li ca my bin th c cu to bi cc l thp mng ghp cch in vi nhau.D. Tng cch in trong my bin th.

5.105.Bin php no sau y khnglm tng hiu sut ca my bin th?A. Dng li st c in tr sut nh.B. Dng dy c in tr sut nh lm dy qun bin th.C. Dng li st gm nhiu l thp mng ghp cch in vi nhau.

D. t cc l st song song vi mt phng cha cc ng sc.5.106. Mt my bin th c s vng cun s cp v th cp ln lt l 2200 vng v 120 vng. Mc cun scp vi mng in xoay chiu 220V 50Hz, khi hiu in th hiu dng gia hai u cun th cp h l

A. 24V. B. 17V. C. 12V. D. 8,5V.

5.107. Mt my bin th c s vng cun s cp l 2200 vng. Mc cun s cp vi mng in xoay chiu220V50Hz, khi hiu in th hiu dng gia hai u cun th cp h l 6V. S vng ca cun th cp l

A. 85 vng. B. 60 vng. C. 42 vng. D. 30 vng.

5.108.Mt my bin th c s vng cun s cp l 3000 vng, cun th cp 500 vng, c mc vo mng inxoay chiu tn s 50Hz, khi cng dng in qua cun th cp l 12A. Cng dng in qua cun s cpl

A. 1,41 a. B. 2,00 a . C. 2,83 a. D. 72,0 a.

5.109.in nng mt trm pht in c truyn i di hiu in th 2kV v cng sut 200kW. Hiu s ch

ca cc cng t in trm pht v ni thu sau mi ngy m chnh lch nhau thm 480kWh. Cng sut in haoph trn ng dy ti in l

A. P = 20kW. B. P = 40kW. C. P = 83kW. D. P = 100kW.


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5.110.in nng mt trm pht in c truyn i di hiu in th 2kV v cng sut 200kW. Hiu s chca cc cng t in trm pht v ni thu sau mi ngy m chnh lch nhau thm 480kWh. Hiu sut ca q utrnh truyn ti in l

A. H = 95%. B. H = 90%. C. H = 85%. D. H = 80%.

5.111.in nng mt trm pht in c truyn i di hiu in th 2kV, hiu sut trong qu trnh truynti l H = 80%. Mun hiu sut trong qu trnh truyn ti tng n 95% th ta phi

A. tng hiu in th ln n 4kV.B. tng hiu in th ln n 8kV.C. gim hiu in th xung cn 1kV.D. gim hiu in th xung cn 0,5kV.

* Cc cu hi v bi tp tng hp kin thc5.112.Trong cc cu sau, cu no ng, cu no sai:

A. Dng in c cng bin i tun hon theo thi gian l dng in xoay chiu. SaiB. Dng in v hiu in th hai u mch xoay chiu lun lch pha nhau. SaiC. Khng th dng dng in xoay chiu m in. ngD. Cng hiu dng ca dng in xoay chiu bng mt na gi tr hiu dng ca n. SaiE. Cng sut tc thi ca dng in xoay chiu bin thiu khc tn s vi dng in. ng

5.113.Mt n non t di hiu in th xoay chiu c gi tr hiu dng 220V v tn s 50Hz. Bit n sngkhi hiu in th gia hai cc khng nh hn 155V. Trong mt giy n sng ln v tt i bao nhiu ln?

A. 50 ln. B. 100 ln. C. 150 ln. D. 200 ln.5.114.Mt n non t di hiu in th xoay chiu c gi tr hiu dng 220V v tn s 50Hz. Bit n sng

khi hiu in th gia hai cc khng nh hn 155V. T s gia thi gian n sng v thi gian n tt trong mt chuk l bao nhiu?

A. 0,5 ln. B. 1 ln. C. 2 ln. D. 3 ln

5.115.Cho on mch xoay chiu gm cun dy c in tr thun R = 100, h s t cm )H(1

L

mc ni

tip vi t in )F(

2

10C

4

. t vo hai u on mch mt hiu in th xoay chiu c dng u =

200sin(100t)V. Biu thc hiu in th tc thi gia hai u cun dy l

A. ud = 200sin(100t +2

)V. B. ud= 200sin(100t +4

)V.

C. ud= 200sin(100t -4

)V. D. ud= 200sin(100t)V.

5.116.on mch xoay chiu gm t in c in dung )F(10

C4

mc ni tip vi in tr thun c gi tr

thay i. t vo hai u on mch mt hiu in th xoay chiu c dng u = 200sin(100t)V. Khi cng sut tiuth trong mch t gi tr cc i th in tr phi c gi tr l

A. R = 50. B. R = 100. C. R = 150 . D. R = 200.p n chng 5

5.1 ChnB.5.2 ChnA.5.3. ChnB.5.4 ChnC.5.5 ChnC.5.6. ChnA.5.7. ChnD.5.8. ChnD.5.9. ChnD.

5.10. ChnD.

5.11. ChnB.5.12. ChnD.

5.13. ChnB.5.14. ChnC.5.15. ChnB.5.16. ChnC.

5.22. ChnB.5.23. ChnC.5.24. ChnA.5.25. ChnD.5.26. ChnB.5.27. Chn B.5.28. ChnB.

5.29. 1- c; 2- a;

3 - b; 4 -c; 5 - b

5.30. 1- c;

2 - e; 3 - b; 4-d.5.31. ChnA.5.32. ChnD.5.33. A(sai),

B(sai), c(ng),D(ng), E(sai)

5.39. ChnD.5.40. ChnD.5.41. ChnC.5.42. ChnC.5.43. ChnC.5.44. Chn C.5.45. Chn D.5.46. ChnD.5.47. ChnA.5.48. ChnC.

5.49. ChnB.5.50. ChnD.

5.51. ChnC.5.52. ChnC.5.53. ChnC.5.54. ChnB.

5.60. ChnA.5.61. ChnD.5.62. ChnC.5.63. Chn B.5.64. ChnB.5.65. ChnC.5.66. ChnA.5.67. ChnD.5.68. ChnA.5.69. ChnC.

5.70. ChnB.5.71. ChnD.

5.72. ChnA.5.73. ChnC.5.74. ChnB.5.75. ChnC.

5.81. Chn B.5.82. ChnC.5.83. ChnC.5.81. ChnD.5.85. ChnD.5.86. ChnC.5.87. ChnB.5.88. ChnA.5.89. ChnA.5.90. ChnD.

5.91. ChnB.5.92. ChnC.

5.93. ChnB.5.94. ChnD.5.95. ChnC.5.96. ChnB.

5.102. ChnC.5.103. ChnD.5.104 ChnC.5.105 ChnA.5.106. ChnC.5.107. ChnB.5.108. ChnB.5.109. ChnA.5.110 ChnB.

5.111. ChnA.5.112. A(sai),

B(sai),

C(ng),D(sai),

E(ung).


14/21



Trang 14

5.17. ChnA.5.18. ChnC.5.19. ChnA.5.20. ChnD.5.21. ChnB.

5.34. ChnB.5.35. ChnC.5.36. ChnD.5.37. ChnB.5.38. ChnA.

5.55. ChnC.5.56. ChnA.5.57. ChnC.5.58. ChnD5.59. ChnB.

5.76. ChnB.5.77. ChnC.5.78. ChnD.5.79. ChnD.5.80. Chn A.

5.97. ChnD.5.98. ChnB.5.99. ChnD.

5.100. ChnA.5.101. ChnA.

5.113. ChnB.5.114. ChnC.5.115. ChnA.5.116. ChnB.

Hng dn gii v tr li chng 5

5.1. ChnB.Hng dn: Dng in xoay chiu bin i iu ho theo thi gian.

5.2ChnA.Hng dn: Khi nin cng hiu dng ca dng in xoay chiu c xy dng da trn tc dng nhit

ca dng in.5.3..ChnB.

Hng dn: in lng chuyn qua mt tit din thng dy dn trong mt chu k bng khng.5.4.ChnC.

Hng dn: So snh biu thc cng dng in xoay chiu i = I0cos(t + ) vi biu thc

i = 2 2 cos100t(A), ta c I0 = 2 2 A

cng dng in hiu dng trong mch l I = I0/ 2 = 2A.5.5.ChnC.

Hng dn: So snh biu thc hiu in th xoay chiu u = U0cost vi biu thc

u = 141cos100t(V), ta c U0 = 141V = 100 2 V

hiuin th hiu dng gia hai u on mch l U = U0/ 2 = 100V.5.6.ChnD.

Hng dn: Xem hng dn v lm tng t cu 5.4.5.7.ChnB.

Hng dn: nh ngha v cng dng in hiu dng nh sau: Cng dng in hiu dng ca dngin xoay chiu l cng dng in mt chiu khng i khi cho chng ln lt i qua cng mt in tr trongcng mt khong thi gian th chng to ra nhng nhit lng bng nhau. Vy khi nim cng dng in hiu

dng c xy dng da vo tc dng nhit ca dng in.5.8.ChnD.Hng dn: Cho dng in mt chiu v dng in xoay chiu ln lt i qua cng mt in tr th chng

to ra nhit lng nh nhau l khng ng, v cha cp ti ln ca cng dng in. Nu mun chng to ra cng mt nhit lng th cng dng in mt chiu phi c gi tr bng gi tr hiu dng ca dng in xoaychiu.

5.9.ChnD.Hng dn: Hiu in th xoay chiu 220V - 50Hz c ngha l hiu in th hiu dng bng 220V, tn s

dng in xoay chiu bng 50Hz.5.10.ChnD.

Hng dn: Nhit lng to ra trn in tr c tnh theo cng thc Q = RI 2t = tRI2

1 20 . Ch i n v t =

30min = 1800s. Q = 900kJ = 900000J.5.11.ChnB.

Hng dn: Hiu in th 119V 50Hz c gi tr cci U0 = 119 2 V = 168V,hiu in th cn thit n sng l 84V = 168/2(V). Da vo mi quan h gia chuynng trn u v dao ng iu ho ta c thi gian n sng trong mt chu k l

s100

3/2.2t

= 0,0133s.

5.12.ChnD.

Hng dn: Dung khngC2

T

C

1ZC

nn t l vi chu k T.

5.13.ChnB.

Hng dn: V in dungd10.9.4

SC

9 nn dung khng ca t in

S

d10.9.4

C

1Z

9

C

c gi tr tng khi d tng.

u(V)

168

84

/6

- 168


15/21



Trang 15

5.14.ChnC.

Hng dn: Cm khngT

L2LZL

nn t l nghch vi T.

5.15.ChnB.

Hng dn: VLZ

UI ;

CZ

UI

5.16.ChnC.Hng dn: Dng in xoay chiu trong on mch ch cha cun cm tr pha hn hiu in th mt gc

/2.5.17.ChnA.

Hng dn: Dng in xoay chiu trong on mch ch cha t in sm pha hn hiu in th mt gc /2.5.18. ChnC.

Hng dn: Dung khng ca t in c tnh theo cng thcfC2

1

C

1ZC

.

5.19. ChnA.Hng dn: Cm khng ca cun cm c tnh theo cng thc fL2LZL .

5.20.ChnD.Hng dn: Xem hng dn 5.16.5.21.ChnB.

Hng dn: Xem hng dn 5.17.5.22.ChnB.

Hng dn: Trong on mch ch cha t in, dng in bin thin sm pha /2 so vi hiu in th. Do phtbiu: Trong on mch ch cha t in, dng in bin thin chm pha /2 so vi hiu in th, l khngng.

5.23.ChnC.

Hng dn: Dung khng ca t in c tnh theo cng thcfC2

1

C

1ZC

.

5.24.ChnA.

Hng dn: Cm khng ca cun cm c tnh theo cng thc fL2LZL .Cng dng in trong mch I = U/ZL = 2,2A.

5.25.ChnD.Hng dn: T biu thc u = 141cos(100t)V, suy ra = 100 (rad/s). Dung khng ca t in c tnh

theo cng thcfC2

1

C

1ZC

.

5.26.ChnB.Hng dn: T biu thc u = 141cos(100t)V, suy ra = 100 (rad/s). Cm khng ca cun cm c tnh

theo cng thc fL2LZL .5.27.ChnB.

Hng dn: T biu thc u = 141cos(100t)V, suy ra hiu in th hiu dng U = 100V v tn s gc =

100 (rad/s). Dung khng ca t in c tnh theo cng thcfC21

C1ZC

. Cng dng in trong mch I

= U/Zc.

5.28.ChnB.Hng dn: : T biu thc u = 141cos(100t)V, suy ra hiu in th hiu dng U = 100V v tn s gc =

100 (rad/s). Cm khng ca cun cm c tnh theo cng thc fL2LZL . Cng dng in trong mchI = U/ZL.

5.29.Chn: 1 - c; 2 - a; 3 - b; 4 - c; 5 - bHng dn: V th i v u t tm ra gi tr ca i khi bit u.

5.30.Chn: 1 - c; 2 - e; 3 - b; 4 - d.Hng dn: Da vo tnh cht mch in ta tm lch pha.

5.31.Chn A

Hng dn:22)C

1L(R

UI

ph thuc vo tn s , do cng ph thuc vo chu k dng in.

5.32.Chn D


16/21



Trang 16

Hng dn: Theo gi thit L

C

1.

Nu ta gim tn s th ZCtng, cn ZLgim cho ti khi ZL = ZCth xy ra cng hng.5.33.A: sai; B: sai; C: ng; D: ng; E: sai.5.34.Chn B.

Hng dn: R ng k + /2, khng chc c cng hng in.5.35.ChnC.Hng dn: Dng in xoay chiu trong on mch ch cha t in sm pha hn hiu in th mt gc /2.

5.36.Chn D.Hng dn: i tr pha so vi u, mch c tnh cm khng nn mc vi cun cm v R.

5.37.Chn B.Hng dn: Cc p n A, C, D c th xy ra nh B lun ng.

5.38.Chn A.Hng dn: hiu in th trn cun du cha chc gi khng i m thay i.

5.39.. ChnD. Hng dn: lch pha gia cng dng in v hiu in th c tnh theo cng thc

R

ZZtan CL

tc l ph thuc vo R, L, C (bn cht ca mch in).

5.40.ChnD.Hng dn: Trong mch in xoay chiu khng phn nhnh khi in dung ca t in thay i v tho mn

iu kinLC

1 th trong mch xy ra hin tng cng hng in. Khi cng dao ng cng pha vi

hiu in th gia hai u on mch, cng dng in hiu dng trong mch t cc i v cng sut tiu thtrung bnh trong mch t cc i. Hiu in th hiu dng gia hai u cun cm t cc i, hiu in th hiudng gia hai u t in v cun cm bng nhau, tng tr ca mch t gi tr nhnht, v hiu in th hiu dnggia hai u in tr t cc i.

5.41.ChnC.Hng dn: Xem hng dn cu 5.40.

5.42.ChnC.Hng dn: Khi mch in xy ra hin tng cng hng in th I max, tng dn tn s dng in xoay chiu

th cng dng in gim, dung khng ca tfC2

1

C

1ZC

cng gim hiu in th hiu dng gia hai

bn cc t in l UC = I.ZCcng gim. Vy khng nh: Hiu in th hiu dng trn t in tng l sai.5.43.ChnC.

Hng dn: Da vo cng thc: UR)ZZ(R

UU

2CL

2R

ta suy ra trong mch in xoay chiu khng

phn nhnh bao gi hiu in th hiu dng gia hai u in tr nh hn hoc bng hiu in th hiu dng giahai u on mch.

5.44. ChnC.

Hng dn: Cng tc tnh tng tr ca on mch RLC mc ni tip l 22 )(CLZZRZ .

5.45.ChnD.

Hng dn: Gi tr cc i ca hiu in th l U0 = U 2 = 12 2 V.Pha ban u ca dng in bng 0 mhiu in th sm pha hn dng in mt gc /3 do pha ban u

ca hiu in th l = /3.5.46.ChnD.

Hng dn: Trong mi trng hp dng in xoay chiu qua in tr thun u bin thin iu ho cng phavi hiu in th gia hai u in tr.

5.47.ChnA.

Hng dn: Cng tc tnh tng tr ca on mch RLC mc ni tip l 22 )(CLZZRZ = 50.

5.48.ChnC.


17/21



Trang 17

Hng dn: T biu thc u = 200cos100t(V) suy ra U = 141V, = 100rad/s vn dng cc cng thc tnh

cm khng fL2LZL , cng thc tnh dung khngfC2

1

C

1ZC

, cng thc tnh tng tr

22)(

CLZZRZ v biu thc nh lut m I = U/Z, ta tnh c I = 1A.

5.49.ChnB.

Hng dn: Xem hng dn v lm tng t cu 5.48.5.50.ChnD.

Hng dn: Dung khng ca mt mch RLC mc ni tip ang c gi tr nh hn cm khng tc l Z C < ZL.Ta gim tn s dng in xoay chiu th ZCtng, ZL gim n khi ZC = ZLth xy ra hin tng cng hng introng mch

5.51.ChnC.

Hng dn: p dng cng thc4

tanR

ZZtan CL

, khi hiu s gia cm khng v dung khng bng

in tr thun ca mch.5.52.Chn C.

Hng dn: Nu c s chnh lch gia u v i th P = IUcos < UI.

5.53.Chn C.Hng dn: lch pha gia dng in v hiu in th gia hai u t in lun l /2. Cng sut dngin khng ph thuc vo i lng ny.

5.54.Chn B.Hng dn: Nu R = 0 th cos = 0.

5.55.Chn C.Hng dn: U = U/Z. thay vo ta thy C ng.

5.56.Chn A.Hng dn: cng thc ch p dng cho mch xoay chiu khng phn nhnh.

5.57.ChnC.Hng dn: Cng sut to nhit trung bnh ca dng in xoay chiu c tnh theo cng thc P = U.I.cos.

5.58.ChnD.

Hng dn: Cng sut ca dng in xoay chiu c tnh theo cng thc P = U.I.cos. Suy ra cng sut cadng in xoay chiu ph thuc vo cng dng in hiu dng I trong mch, hiu in th hiu dng U giahai u on mch, bn cht ca mch in v tn s dng in trong mch (c trng bi lch pha .

5.59.ChnB.Hng dn: i lng k = cos c gi l h s cng sut ca mch in xoay chiu.

5.60.ChnA.Hng dn: H s cng sut k = cos. Cc mch:+ in tr thun R1ni tip vi in tr thun R2c =0.+ in tr thun R ni tip vi cun cm L c 0 <


18/21



Trang 18

Hng dn: Xem hng dn cu 3.64.; cng dng in hiu dng trong mch l I = U/Z = 0,328A. innng tiu th trong 1 pht l: A = P.t = UItcos = 220.0,328.60. 0,4469 = 1933J. C th tnh theo cch khc: innng tiu th trn on mch chnh bng nhit lng to ra trn in tr R v c gi tr bng Q = RI2t.

5.66.ChnA.

Hng dn: p dng cng thc tnh cng sut P = kUI (k l h s cng sut), ta suy raUI

Pk = 0,15.

5.67. ChnD.Hng dn: Sut in ng ca my t l vi tc quay ca rto.

5.68. ChnA.Hng dn: Bin ca sut in ng t l vi s cp cc p ca nam chm:e = 2fN0 = 2npN0.

5.69. ChnC.Hng dn: Nguyn tc hot ng ca my pht in xoay chiu mt pha v ba pha u da trn hin tng

cm ng in t.5.70.ChnB.

Hng dn: Nguyn tc hot ng ca my pht in xoay chiu mt pha da vo hin tng cm ng int: Cho t thng qua mt khung dy dn bin thin th trong khung dy xut hin dng in cm ng.

5.71.ChnD.Hng dn: Hin nay vi cc my pht in cng sut ln ngi ta thng to ra dng in xoay chiu mt

pha bng cch cho cun dy ng yn, nam chm vnh cu chuyn ng quay trong lng stato c cun cc cundy. Cc my pht in c cng sut ln th dng in i qua cun dy ca phn ng phi ln, khng th dng bgp in ly in ra s dng.

5.72.ChnA.Hng dn:- Tn s ca sut in ng ph thuc vo tc quay ca rto phn cm, v s cp cc t ca phn cm.- Bin ca sut in ng E0= NBS ph thuc vo phn ng.- C nng cung cp cho my mt phn bin i thnh in nng, mt phn bin i thnh nhit nng.- Dng in cm ng ch xut hin cc cun dy thuc phn ng.

5.73.ChnC.

Hng dn: Tn s ca sut in ng cm ng do my pht in xoay chiu to ra c tnh theo cng thc

60

npf trong p l s cp cc t, n l s vng rto quay trong 1 pht.

5.74.ChnB.Hng dn: Sut in ng cc i gia hai u cun dy phn ng l E 0= N.B.S. = N.0. = N.0.2f

vi 0l t thng cc i qua mt vng dy ca cun dy trong phn ng. 0 = 2mWb = 2.10-3

Wb.

5.75.ChnC.Hng dn: Xem hng dn cu 6.74.

5.76.ChnB.Hng dn: Xem hng dn cu 5.74. v 6.75.

5.77.Chn B.Hng dn: sut in ng t l vi s vng dy.

5.78.ChnD.Hng dn: Theo nh ngha v dng in xoay chiu ba pha: Dng in xoay chiu ba pha l h thng ba

dng in xoay chiu mt pha gy ra bi ba sut in ng c cng tn s, cng bin , lch pha nhau 1200.5.79.ChnC.

Hng dn: Trong cch mc hnh sao hiu in th gia hai dy pha bng 3 ln hiu in th gia hai umt pha.

5.80.ChnA.

Hng dn: Trong cch mc hnh tam gic dng in trong mi dy pha bng 3 ln dng in trong mipha.

5.81.ChnB.Hng dn: Vi cch mc hnh tam gic ch dng c 3 dy dn, cng l s dy dn cn dng l t nht.

5.82.. ChnC.

Hng dn: Trong cch mc hnh sao c Ud = 3 Up = 220 3 = 381V.5.83.ChnC.

Hng dn: Trong cch mc hnh tam gic c Id = 3 Ip = 10 3 = 17,3A.


19/21



Trang 19

5.84.ChnD.Hng dn: Ba cun dy ca my pht theo hnh sao th hiu in th hiu dng gia hai dy pha l Ud =

3 Up = 127 3 = 220V. Ba cun dy ca ng c theo hnh tam gic th hiu in th hiu dng t vo mi cundy ca ng c l 220V, ng c hot ng bnh thng.

5.85.ChnD.Hng dn: Vn tc gc ca ng c khng ng b ba pha tng khi vt tc ca t trng quay tng, gim

khi momen cn tng, nn ph thuc vo c hai yu t ny.5.86.ChnC.

Hng dn: Nguyn tc hot ng ca ng c khng ng b ba pha l da trn hin tng cm ng in tv tc dng ca t trng quay.

5.87.ChnB.Hng dn: So vi ng c in mt chiu, ng c khng ng b ba pha c hiu sut cao hn.

5.88.ChnA.Hng dn: Xem hng dn v lm tng t cu 5.84

5.89.ChnA.Hng dn: Ngi ta c th to ra t trng quay bng hai cch:Cch 1: Cho nam chm vnh cu hnh ch U quay u quanh trc i xng ca n.

Cch 2: Cho dng in xoay chiu ba pha chy qua ba cun dy trong stato ca ng c khng ng b bapha.5.90.ChnD.

Hng dn: Xem hng dn cu 5.72.5.91.ChnB.

Hng dn: Cm ng t do c ba cun dy gy ra ti tm stato ca ng c khng ng b ba pha khi cdng in xoay chiu ba pha i vo ng c c ln khng i, hng quay u vi tn squay bng tn s dngin.

5.92.ChnC.Hng dn: Tng hp ba vct cm ng t do ba cun dy trong Stato ca ng c khng ng b ba pha

gy ra ti tm ca stato theo quy tc cng vc t, ta s c B = 1,5B 0.5.93.ChnB.

Hng dn: Trong stato cang c khng ng b ba pha mi cp cc gm ba cun dy. Trong stato c 6cun dy tng ng vi p = 2 cp cc, khi t trng ti tm ca stato quay vi tc n = 60f/p = 1500vng/min.5.94.ChnD.

Hng dn: Trong stato ca ng c khng ng b bapha mi cp cc gm ba cun dy. Trong stato c 9cun dy tng ng vi p = 3 cp cc, khi t trng ti tm ca stato quay vi tc n = 60f/p = 1000vng/min.ng c khng ng b nn tc ca rto bao gi cng nh hn tc t trng quay, suy ra rto lng sc cang c c th quay vi tc 900vng/pht.

5.95.ChnC.Hng dn: Nguyn tc hot ng ca ng c khng ng b ba pha da trn hin tng cm ng in t

v lc t tc dng ln dng in.5.96.ChnB.

Hng dn: Sut in ng ca my pht in xoay chiu c tnh theo cng thc E0= N.B.S. suy ra E t

l vi s vng quay () trong mt pht ca r to.5.97.Chn A.

Hng dn: My pht in mt chiu c tnh thun nghch.5.98.Chn B.

Hng dn: Cc cun dy ca my bin p u c cun trn cc li st tng cng t trng, gim tnhao t thng.

5.99.Chn D.Hng dn: Nu tng R hai ln th P gim 2 ln.

5.100.Chn A.Hng dn: ch n nh, cng sut hao ph k0 i, khng ph thuc vo thi gian truyn ti in.

5.101.Chn A.Hng dn: Ni chung R nh song ch gim n mc no .

5.102.ChnC.Hng dn: My bin th c tc dng bin i hiu in th cn tn s dng in xoay chiu vn c gia

nguyn.

5.103.ChnD.


20/21



Trang 20

Hng dn: Hin nay trong trong qu trnh truyn ti i xa, ngi ta thng tng hiu in th trc khitruyn ti in nng i xa.

5.104.. ChnC.Hng dn: Li ca my bin th c cu to bi cc l thp mng ghp cch in vi nhau nhm gim bt

dng in Phuc, lm gim hao ph in nng trong my bin th.5.105.ChnA.

Hng dn: Xem hng dn cu 5.845.106.ChnC.

Hng dn: p dng cng thc my bin th:2

1

1

2

2

1

N

N

I

I

U

U

5.107.ChnB.Hng dn: Xem hng dn v lm tng t cu 5.86

5.108.ChnB.Hng dn: Xem hng dn v lm tng t cu 5.86

5.109.ChnA.Hng dn: Hao ph trn ng dy ti in trong mi ngy m l 480kWh, suy ra cng sut hao ph trn

ng dy ti in l P = 480kWh/24h = 20kW.

5.110.ChnB. Hng dn: Cng sut hao ph trn ng dy ti in l P = 20kW, suy ra hiu sut truyn ti l

%90200

20200

P

PPH

5.111.ChnA.Hng dn: Cng sut truyn ti khng thay i, p dng cng thc tnh hao ph trn dy dn do to nhit

2

2

U

rPP hiu sut truyn ti in nng i xa l

2U

rP

P

PH1

P

PPH

, suy ra

21

1U

rPH1 v

22

2U

rPH1

21

22

2

1

U

U

H1

H1

kV4U16

95,01

80,01.2U 2

222

5.112.A sai; B sai; C ng, D sai, E ng.5.113.ChnB.Hng dn: Trong mt chu k n sng ln 2 ln suy ra trong mt giy, vi dng in xoay chiu 50Hz th

n sng ln 100ln.5.114.ChnC.

Hng dn: Xem hng dn v lm tng t cu 5.115.115.ChnA.

Hng dn: T biu thc u = 200sin(100t)V ta c hiu in th hiu dng gia hai u oan mch l U =

100 2 V, tn s gc ca dng in xoay chiu l = 100(rad/s).Cm khng ca mch l ZL= L = 100.

Dung khng ca mch l ZC =C

1

= 200.

Tng tr ca mch l 22 )(CLZZRZ = 100 2 .

Cng dng in trong mch lZ

UI = 1A.

Hiu in th hiu dng gia hai u cun dy l 2L2

d ZRIU = 100 2 V.

Thy ZL < ZCnn on mch c tnh dung khng, cng dng in trong mch sm pha hn hiu in th

gia hai u on mch mt gc c4

1R

ZZtan

CL

. Suy ra biu thc cng dng in trong

mch c dng i = 2 sin(100t + /4) A.Xt on mch cha cun dy (RntL), nn on mch c tnh cm khng, hiu in th gia hai u cun dy

sm pha hn cng dng in trong mch mt gc 1 c4

1R

Ztan 1

L1

. Suy ra biu thc ca hiu

in th gia hai u cun dy l ud= 200sin(100t +2

)V.


21/21



5.116.ChnB.Hng dn: T biu thc u = 200sin(100t)V ta c hiu in th hiu dng gia hai u oan mch l U =

100 2 V, tn s gc ca dng in xoay chiu l = 100(rad/s).

Dung khng ca mch l ZC =C

1

= 100.

Tng tr ca mch l 2C2 ZRZ .

Cng dng in trong mch lZ

UI .

Cng sut tiu th trong mch l P = RI2 =2C

2

2

ZR

RU

(*), cng sut tiu th trong mch t cc i th R

0, chia c t v mu ca (*) cho R ta cC

2

2C

2

Z2

U

R

ZR

UP

= 100W.

Suy ra Pmax = 100W khi R = ZC= 100.

on tap ltbt chuong ddxc co dap an va huong dan

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