D. ROLE 3.1 Ca'u t:;io:
b. Cau t�o m?t ngoai c Cau t�o phfa trong.
c. Cau t�o phfa trong.
3.2 Nguyen ly lam vi�c:
Nguyen ly chung cua rdle nhi$t la dlfa tren cd sd tac d1,mg nhi$t cua dong di$n. Ngay nay ng- di ta Crng d1,mg r(:mg rai rdle nhi�t c6 phien kim loc;:ii kep.
Nguyen ly tac d1.,mg cua lo9i rdle nay la dlfa tren slf khac nhau ve h� so gian nd dai cua hai kim 109-i khi bi dot n6ng. Do d6, phan tll' cd ban cua rdle nay la phien kim lo9i kep c6 cau tc;:io ta hai tam kim loc;:ii. M9t tam la invar (H36 c6 36% Ni, 64% Fe), c6 h� so gian
nd dai be va m9t tam khac th- dng la dong thau (ho?c thep Crom- Niken), c6 h$ so gian nd dai lefn (th- dng lefn hdn 20 Ian). Hai tam kim lm;ii nay d- <;,c ghep ch?t lc;:ii vefi nhau bang ph- dng phap can n6ng ho?c han de tc;:io thanh m9t phien. Ta g9i n6 la phan tll' dot n6ng hay I- ang kim nhi$t.
Khi qua tai, dong di$n phl:J tai qua phan tll' dot n6ng tang len, nhi�t d9 cua phan tU' dot n6ng se nung n6ng phien kim loc;:ii kep. Do d9 gian nd nhi$t khac nhau, ma 19i b! gan ch?t hai dau nen thanh kim 109-i kep se bi uon cong ve phfa thanh kim lo9i c6 d9 gian nd nho.
Slf phat n6ng c6 the do dong di$n trlfc tiep di qua phien kim lo9i ho?c gian tiep qua di$n trd dot n6ng d?t bao quanh phien kim lo9i.
m1lffllJ I � 11 [Eff,� 4,;-;;::�j+-
Phan tll' dot n6ng g1an t1ep.(ldong dlE?n di quaca,E?n trd d?t bao quanh phien kim loc;:ii Phan tll' dot n6ng trlfc tiep (dong di$n di trlfc tiep qua phien kim lo9i)