I) Khi CO hai gid tri Ri vii R2 dcPi =P2 =P thi:
0,5o)i/V2 B (01V2 W1/V2 D.2 (01.
v^i f t ^jrmr^TCWt nKMMn-rTV^, t^p jr — « ntt van OiCfT'
Huong dan
=> = 2coL = > CI) = —? = V 2 = CO, v 2 => Chon B
coc 2VLC ' ;' . '
V i du 4: Dat dien ap xoay chieu c6 bieu thirc u = U >/2 coscot (V) (trong do U va
CO khong doi) vao iiai dau AB ciia mot doan mach gom doan mach A M noi tiep voi doan mach M B . Doan mach A M c6 cuon cam thuan c6 do t u cam L
va bien tro R mac noi tiep, doan mach M B chi c6 tu dien c6 dien d u n g C. Biét rang co = (2LC)~^''''. K h i thay doi bien tro den cac gia t r i R i = 50 Q, R2 =
100 Q va R 3 = 150 Q thi dien ap hieu d u n g giua hai diem A M c6 gia t r i Ian lugt la U i , U2, U3. Ket luan nao sau day la dung? M l ;
Ạ U l < U 2< U 3 . B. U l > U 2> U 3 . C. U l= U 3> U 2 . D. U l = U 2= U 3 .
Huong dan ,.,
Z C= 2Z , = ^ U „ L = I Z K , , = U R- + Z f
= U g R = > C h o n D . ; i
V i d\ 5: Xet mach dien AB gom cac phan t u mac noi tiep theo t h u t u la cupn
day thuan cam c6 do t u cam L, dien tro thuan R, tu dien c6 dien d u n g C. Gt)i M la diem noi giua L va R, N la diem noi giua R va C. Dat vao A, B mot dien ap xoay chieu c6 gia trj hieu d u n g U khong doi va tan sógoc co thay doi duc7c. K h i Ian l u o t cho co cac gia trj c o i , C02, co3 thi Ian l u o t dien ap hieu d u n g giOa hai dau M N , giua hai dau A N , giua hai dau M B deu bang U . K h i do, he thuc d u n g la:
Ạ C 0 3 = C02/>y2 = coi/2. • • , B . C 0 3 = N/2 C02 = 2coị ^^. C. C03 = C02/2 = coi/V2 . < D. C03 = 2co2 = coi 72 .
Huong dan
CO, xay ra ccing h u o n g dien nen coi = . —
v L C
lam cho U,^L = '^ci = 2Z[,2 => = ^
(!), lam cho U[^(j = U nen Z, 3 = IZ^^ =>o)3 = 4i
VLC
S u y r a 0)3 =2co2 =c)|V2 =:> Chon D . ' ^
Vi du 6: Cho mot doan mach xoay chieu gom dien tro thuan R thay doi dugc, cuon day thuan cam L va tu dien C theo thii t u mac noi tiep voi nhaụ Dat vao hai dau doan mach mcit dien ap xoay chieu co gia tri hieu d u n g 200 V
50 -^...^r • •
tan só f thay d o i dugc. K h i f = 50 H z thi cuong do dong dien hieu d u n g
trong mach la 2 A va d i f n ap hieu d u n g giu-a hai dau RL khong thay d o i k h i p thay d o i . Dien d u n g nho nhat cua tu dỉn la
Ạ 25/7t C^iF). B. 50/71 (^iF). C. 0,l/7i (|aF). D . 0,2/7t (^iF).
Huang dan = ỊZRT = u . u ^ ^ ^ ^ , . R « = ( Z , - Z c = > Z c = 2 Z , Z . 7 F 7 z [ = y = 100Q R 2 + ( Z L - Z C ) Z L< 1 0 0Q 1 ' 50 .10-*' (F) ^ Chon B. ^Zc^ 2ZL < 200Q n> C > ^ 10071.200
Vi d v 7: (DH-2010) Dat dien ap xoay chieu co gia t r j hieu d u n g va tan so khong doi vao hai dau doan mach gom bien tro R mac noi tiep v o i t u dien co di^n dung C. Ggi dien ap hieu d u n g giiia hai dau tu dien, giiia hai dau bien tro va he s o c o n g suát ciia doan mach k h i bien tro co gia t r i R i Ian l u g t la U c i , URI va coscpi; k h i bien tro co gia trj R2 thi cac gia t r i t u o n g u n g noi tren la
Uc2, UR2 va coscp2. Biét U c i = 2Uc2, UR2 = 2URI. Gia trj cua coscpi va coscp2 la: Ạ coscpi = 1/N/3 , coscp2 = 2/V5 . B. coscpi = \lsl5 , coscp2 = 1/73.
C. coscpi = 1/75 , COSCP2 = 2/75 .-- ' ' D. coscpi = 0,5/72 , coscp2 = 1/72 . (adsbygoogle = window.adsbygoogle || []).push({});
Huang dan i . , ' ' i •ifi 7,, J<1 ; i I = ^ = Z u = I Z , n n = 2 U o^ i i= 2 i ? ^ Z 2 = 2 Z i +z^" = 2 JifTz^ R . r = 2- R i Ri 1 " R 2 = 4 R i Z r - 2 R i coscpi = COSCP2 ^ => Chon C.