C. 4,35Q d 2,175n
c) Nonh lualt Ohm phalt bieu nho sau:
Doi v&i m9t nhanh bat ky trang m9ch ta tf ch so giG'a tU' thong chay qua va t6ng trb W bang tCt ap re1i giG'a hai dau cua nhanh d6.
(4.3) Trang cac cong thuc tren:
- <Di: la ta thong chay qua cac nhanh cua m9ch tU' (wb). Fi: la sue tCt d9ng cua cac nhanh tCt t- e1ng ung (A.t). Rmk: ta trd cua nhanh tCt t- C1ng ung (11H).
Zmi : t6ng trb tCt cua cac nhanh (11H). - Umi : ta ap re1i tren cac nhanh tCt (A).
Tong trc:5 Zmi cua nhanh tU' bao gom hai thanh phan la tU' trb Rmi va tCt khang Xmj, giG'a chung c6 quan h$ tam giac vuong.
(4.4)
0oi v6i m9ch ta m9t chieu (DC) kh6ng ton t9i thanh phan tCt khang Xmi v1 v{J.y trang d6 chi bao gom cac thanh phan ta trb Rmi·
R .=-!,_ . .
m, S
A; (4.5)
Trang d6:
- 11 : la chieu dai cua nhanh tCt t- e1ng ung (m). - S1: tiet di$n cua nhanh tCt d6 (m2).
µ1 : la ta tham vif}t li$u tCt cua nhanh tCt t- e1ng ung (Him). Vf du:
M9ch ta d-c;JC tr1nh bay nh- (h1nh 4.3). Loi d-c;JC lam W vif}t li$u W c6 d9 tCt
tham µ 16n he1n rat nhieu v6i tCt tham cua chan khong µ0 v6i: µ0 = 4rc.1O-7 (Him). Loi c6 tiet di$n kh6ng doi va d-c;5c kfch tCt bc:5i cu9n day c6 N vong day, trang
d6 chay dong di$n I (A). Cu(:m day N se sinh ra tCt tr- e5ng trang loi thep va d-c;Jc bieu
dien trang (h1nh 4.3).
{fl /' -, I .---:;;,o":;rr--------, I 0 - - + - + - I ~ / A I I I :+( Hlrih 4.3: M~ch tu' S /
TU' thong <I> di qua be m~H S bang tfch phan m$t cua cac thanh phan phap tuyen cua W cam B. Nh- v$y.
(4.6) Trong h$ do I-crng s I, W thong <I> c6 th Ct nguyen la weber (wb).
Khi tU' cam la dong nhat ben trong mc)t m$t cat bat ky cua 16i thep, ph- cmg tr1nh tren c6 the d-C1c bieu dien:
(4.7) Trang d6:
- <I>i : tll' thong trong 16i thep.
- Si : la tiet di$n cua 16i thep.
TU' ph- e1ng tr1nh f H.dL = f J.dS, quan h$ giU'a sCtc tll' dc)ng va c- crng de) W
C S
tr- C1ng H c6 the d- <;Jc bieu dien:
F = NI = f H. dl . (4.8a)
Loi thep c6 de) dai trung b1nh chfnh bang chieu dai khep kf n cua d- crng sCtc W
bat ky Ii.
Ket qua la tfch phan d- crng (4.8) trd thanh tfch cua cac d<?i I-qng v6 h- 6ng Hi, Ii. TU' ph- C1ng tr1nh (4.8a) c6 the viet l<?i:
(4.8b)
Vcri Hi la gia tr! trung b1nh phan thlfc cua vecto H trong 16i thep. Chieu cua Hi trong 16i thep d- 9c xac d!nh theo quy tac ban tay phai, n6 c6 the d- 9c bieu dien bang hai each t- ong tl/ nh- nhau. Hay h1nh dung rang c6 m(>t v$t dan di$n d~t trong ban tay phai, ng6n tay cai chi chieu cua tu tr- ong Hi. Hoan toan t- ong tl/ neu nh- cu(>n day trong h1nh ve (h1nh 4.3) d- 9c nam bai ban tay phai, khi d6 cac ng6n tay chi chieu dong di$n va ng6n tay cai se chi chieu tu tr- dng.
Trong moi nhanh tu cua m<?ch tu, quan h$ giU'a tu cam Bi (T) va c- dng d9 tu
tr- ong Hi (Alm) d- 9c bieu dien bang d- Ong cong tu h6a B = f(H) cua v$t li$u tu nh$n d- 9c tu thlfc nghi$m. 0oi vcri cac v$t li$u phi tu tf nh nh- dong nhom, dong v.v ... , cac v$t li$u each di$n nh- Fibre, bakelite v.v ... va khong khf, quan h$ nay d- oc bieu dien nh- sau:
B = µ0.H.
Vcri µ0 la tu tham cua chan khong (H/m). Trong m9ch tu ta phan bi$t cac tu tho11g sau:
(4.9)
♦ Tu thong lam vi$c ©1v la tu thong di qua khe ha khong khf chf nh cua m<?ch
tu.
♦ Tu thong ro <l)o la tu thong khong di qua khe ha khong khf chf nh cua m9ch tu ma khep kf n theo cac d- ong khac.
♦ Tu thong tong ©0, la tong cua hai tu thong ©1v va ©8 va th- dng di qua phan gong cua m9ch tu (h1nh 4.3).