. A 0,6 B 0,866 C 0,8 D 0,
A. 230 W B 394 W C 256 W D 300W.
^hdn tich m huang ddn gidi
Cong suat tren R dat eye dai thi R = ^r^+CZ^-Z^)^ = 1OV6TQ ,
2r + 2 ^ r 2 + ( Z L - Z c ) ^
•=256W
Chpn dap an C
^^U 6: Cho mach di?n nhu hinh ve: R la bien tro UAB = lOOv'2 V; UAN =
100N/2 V ; UNB = 200V. Cong suat eiia mach la P = 100 V 2 W . Cong suat eye dai ciia mach
A. P =p ^ max ^ max C P >p max ^ ^ B P m a x < P D . P „ , a x=2P
^ h d n tich vd huang dan gidi
Ta c6:
U^B = + ( U L - U C ) ^ U ^ N = + U ^ U ^ B = Uc = 200V
U A N = U A B U, • UR =100V
Vay UR=|UL-Uc|->R = | Z L - Z c | ^ P = PMax Chon dap an A
Cau 7: Cho mach dien xoay chieu AB chua R,L,C mac noi tie'p. Doan A M c6
dien tro thuan va cuon day thuan cam 2R = Z^, doan MB c6 dien dung C c6
the thay doi dugc. Dat vao 2 dau doan mach hieu dien the xoay chiOu u = U(, cosfot CO U„ va m i<h6ng doi. Thay doi C = C(, cong suat mach dat gia tri CD, i<hi do mac them tu C, vao mach MB cong suat mach giam I nua, tie'p tuc mcic them tu Cj vao mach MB de cong suat mach tang gap doi. Tu C, CO the nhan gia trj nao sau day:
A. ^ hoac 3C() B. Cn hoac 3C, 0
C. hoac 2C 0 D. hoac 2C, 0
'Phdn tich vd haang dan gidi Luc dau do cong huong nen 2 ^ = 2 ^ = 2R
De cong suat doan mach giam 1 nua tuc la sau khi ghep them Ci thi dung khang cua bo tu phai thoa man [Z^ - | = R nen xay ra 2 truong hop:
Truong hgp 1: Z^^ > Z^ nen lap tu Ci noi tie'p voi Co ta c6 liic do
Z„=3R = ^ . ^ 2
Vay de cong suat lai tang 2 Ian thi luc do lai c6 Z^ = 2R . Tiic phai m^c tu C2 song song voi Co va Ci khi do
1
ZQ = 6R — 3Z(~-()
Truong hgp 2: Tuong tu cho Z^ < Z^ tuc la:
Z r
Zc = R = > Z c 2 =R = — = ^ C 2 =2Co
Chgn dap an D
350
Ci
C§U 8: Mot doan mach noi tie'p gom cuon day c6 dien tro thuan r 100\/2 Q va
do tu cam L = 0,191 H, ty dien c6 dien dung C = l/4Tc(mF), di#n tro R c6 gia tri
thay doi duoc. Dien ap dat vao hai dau doan mach u = 200 V2 cos(1007rt) V. Thay doi gia tri ciia R de cong suat tieu thu trong mach dat cvfc d ^ , gia trj cue daidola
A.200W B.277,3W C. lOOW D.50W
^h&n tich v>d huang ddn gidi
Dien tro ciia cuon day: r = 100\/2 Q
Cam khang ciia cuon day: Z L =toL = 0,191.10071 = 60 Q . ' Dung khang ciia tu: ZQ = = —roC = 40Q
lOOTt. 1 0 ,-3
47t
Cong suat tieu thy tren mach: P =
(R + r) + ( Z L - Z C ) ' . ( R . r ) Ptnax ^ R + '' = |ZL-Zc|=>R=|ZL-Zc|-r = |60-40 -IO0V2 <0 • P m a x « R = OVay -.r = 200^ r +{Z^-Z^) (looVi + (60-40)^ -.100N/2 = 2 7 7 , 3 ( W ) Chpn dap an B
Cau 9 : Cho doan mach RLC mac noi tie'p: cuon day thuan cam c6 dp tu cam L, tu
dien CO dien dung C, R thay doi dupe. Dat mpt di|n ap xoay chieu on djnh a
hai dau doan mach c6 U = lOOV, f = 50Hz. Dieu chinh R thi thay c6 hai gia trj 30Q va 20Q mach tieu thu ciing mpt cong suat P. Xac dinh P liic nay?
A. 4W. B. lOOW. C. 400W D. 200W.
(Phdn tich m huang dan gidi
Bai niy da qua quen thuoc vi thechi cam mat khodng 10 giay la c6 ngay dap an.
P = 100'
R j + R 2 = 200W 30 + 20
Chpn ngay dap an D
ijCau 1 0 : Dat mpt dien ap xoay chieu c6 gia trj hi?u dyng IOON/S V va tan so
50Hz vao hai dau doan mach AB gom dien tro thuan 40 Q mic noi tie'p voi
hop kin X (hop X chua hai trong ba phan tu r, L, C mac noi tie'p). Cuong dp dong di^n hi^u 'uag qua m^ch bang 3A. Tai thai diem t cuong dp dong
di#n qua mach bang 3\/2 A, den thai d i e m t'= t+ 1/300 (s) d i ^ n ap hai dau doan mach bang khong va dang giam. Cong suat tieu thy tren hpp k i n X la A . 90W B. 120W C. 75x/3W D . I S o T s W