Nam chAm vInh CW. Dam cham dien. dAy dAn mang dong dien t"o ra xung quanh ChuDg tit truOng. TIl' trutrng dUQ'c bieu di~D bang cae duang sUe tll'
truang (duang cim ling til) di til C\f'C bAe (N) tm qrc Dam (S) va tra v~ c1,lC bAC qua loi nam cham (hlnh 2.1a, b) .
• N
b)
Ni"h 2.1. Dubng site CUB Dam cham a} Dam cham vinb diu; b) Dam cham di(!n
D6i v6'i dAy dan thing dlLi mang di~n. chi~u til t!trang dug<: xac dlnh thea
quy tac v~ mlt chai: n~u chi~u dong di¢n trnng v6i chi~u ti~n ella cai rna nut
chai thi chi~u quay ella cai rna nut chai xac dinh cho ta chi~u to' trubng a mOi diem (bloh 2.2.).
Ta cilng co the Slr dl,lDg quy tAc ban tay phai (hinh 2.2b) : ng6n lay cai
hll'6ng theo chi~u dong di¢n. b6n ng6n t~y con l~ chi bu6ng dtrOng sUe tit
truOng.
28
.J bJ
HI"h 2.2. Xac djnh chiiu d.rong sil'c 111 Ifl1img cua day dAn thing mang dbng di~n D6i v6i cUQn dAy gdm m(H
s6 vbng day c6 dbng di~n ta ding dung quy tAc rna mit chai de xac dinh chi~u dubng sire til
tIlIOng: n~u chi~u quay eua cai
rna nut chai trI)ng v6i chi~u dbng
di~n thl chi~u tit!n ella cai rna
nut chai III chi~u dutmg sUe ttt
,mang (hinh 2.3).
Sg c6 m~t cDa tir truang trODg kbdng gian
d~c trung bAng cae bien
hi¢n sau :
1. LJ!e tit gth de
C\l'C cua nam chAm
HiRh 2.3. Xac djnh chi~u dlJ('mg sUe lit uubng cua cu(ln dAy c6 dbng di~n
Hai c\I'C· We ten ciJ.a 2
nam chAm ~ gin nhau~ se
hu, nhall (hlnh 2.4). NgllI;lt
t~ 2 c,,", cflng ~ d.! ~
Mall sl! d.Ily Mall (hlnh 2.5). Hlah 2.4. L1!c hut giii'll 2 el,lC thac Itn ella 2 nam cham
29
2. LIfC di~n tu
LlIc tac d\lDg Ifn day dAn c6 dong di~n
d.Jt trong tll trucrng ho~c
di¢n tich dang chuyen
~g trong tll truang.
i
'" ,: 3. Cam -ung di~n tu
;
,_ . Sq xul!t hi~n suc di~n
~g cam Ung vAo m"t Hlnh 2.5. L.,c day ,iita 2 CI!C cung len cua 2 nam chAm vOng dAy khi tll lTlWng bi6n thifn ho~c thanh dAn chuyen d"ng lrong tll truimg .