

&
GIÁO ÁN VẬT LÍ 9


NĂM HỌC
Ngày soạn: Ngày giảng:. Tiết 1:
CHƯƠNG I: ĐIỆN HỌC.

 
1
1
Kin thc:
-!"#$%&'()*+(,-!.'/#01
2'()*+(%3-#45+6718#9:;9<-+=>%"#4,!?@-#?@-A"+(,-!B()*+
#C-!$D->#!)E->FG>%H!%3'(%3-#!I(J#K@?!7%(L'9:;9<-K@+)M->(8
9N->(%3-+!O;P'7-=!/-$%I#()*+(E-K,+67(%3-#45
2'()*+(J+(%&1KQ+)M->(89N->(%3-BKQ!%3'(%3-#!IK@(%3-#45
#)E->()E->(G%KR%(?O-1O+!-G%#%ISK@(?O-1O+!F?->F?->
2'()*+1G%P'7-!3>%H7(%3-#45+679:;9<-KR%+!%Q'9@%B#%I#9%3-K@
K/#.%3'.@19:;9<-
2'()*+$%I-#45.@>TK@+"+9U'!%3'-!/-$%I#(%3-#45#4?->VW#!'/#
2'()*+X->!Y7+"+#4,FGKZ-K@?"#>!%#42-#!%I#$,#%2'#![(%3--\->
%I#()*++"++Z->#!]+#C-!+Z->F'U#(%3-K@(%3--\->#%2'#![+6718#
(?O-1O+!
2'()*+18#FG9U'!%3'+!]->#^9N->(%3-+=-\->.)*->
!_47()*+F`+!';&-!=7+"+9O->-\->.)*->V!%(a-(%3-B$IS(%3-B
$@-.@B-71+!:1(%3-B(Z->+E(%3-!?O#(8->
K! năng:
b"+(,-!()*+(%3-#45+6718#(?O-1O+!$D->KZ-VIK@71ScVI

.)*->+N-.O%K@>%m%#!C+!()*++"+!%3-#)*->(E->%m-.%2-P'7-(I-(%3-
#45+679:;9<-
%m%#!C+!()*+->';2-#n+!?O#(8->+67$%I-#45+?-+!O;o9[->()*+
$%I-#45(&(%Q'+!_-!+)M->(89N->(%3-#4?->1O+!
/-9[->()*+(,-!.'/#01K@+Z->#!]+ed
S
l
(&>%m%$@%#?"-KQ1O+!
(%3-()*+Fo9[->KR%!%3'(%3-#!IV!Z->(p%B#4?->(=+=1n+$%I-#45
b"+(,-!()*++Z->F'U#(%3-+6718#(?7-1O+!$D->KZ-VIK@71ScVI
/-9[->()*++"++Z->#!]+pejep#e#(&#C-!()*+18#
(O%.)*->V!%$%I#+"+(O%.)*->+N-.O%(G%KR%(?O-1O+!#%2'#![(%3--\->
2
2
/-9[->()*+(,-!.'/#q'-c-AE(&>%m%#!C+!+"+!%3-#)*->(E->%m-
+=.%2-P'7-
%m%#!C+!()*+#"+!O%+67!%3-#)*->(?m-1O+!K@#"+9[->+67+L'+!T(&
(m1$m?7-#?@-(%3-
%m%#!C+!K@#!`+!%3-()*++"+$%3-S!"S#!Z->#!)M->(&Fo9[->7-#?@-
(%3-K@Fo9[->#%I#V%31(%3--\->
Bài 1: SỰ PHỤ THUỘC CỦA CƯỜNG ĐỘ DÒNG ĐIỆN VÀO
HIỆU ĐIỆN THẾ GIỮA HAI ĐẦU DÂY DẪN.

fr%I-#!]+
2'()*++"+!$G#4CK@#%I-!@-!#!C->!%31V!m?F"#F`S![#!'8++67+)M->
(89N->(%3-K@?!%3'(%3-#!I>%H7!7%(L'9:;9<-
sK@Fo9[->()*+(l#!,$%&'9%t-1G%P'7-!3B#uFG.%3'#!`+->!%31
2'()*+VI#.'/-KQF`S![#!'8++67+)M->(89N->(%3-K@?!%3'(%3-#!I
>%H7!7%(L'9:;9<-
hrY-\->n+1O+!(%3-#!c?FE(l

fKZ-VI+=>%R%!O-(?…Bfh
f+Z->#n+
f->'l-(%3-18#+!%Q'…
+"+(?O-9:;-G%
 4`+P'7-B#!`+->!%31
3
3
A
V
K
V
A
+
-
Đoạn dây dẫn đang xét
1
2
3
4
56
K
!Z->$"?9O->(l#!,#uVI#P'mKR%18#9:;9<-V!"+
†|y‡|v
ˆyfy‰†Šv‹0
r%&1#47FYFG.RS
2';2'+L'(G%KR%1Z-!w+KQF"+!K5B(l9Œ->!w+#/S
%R%#!%3'+!)E->#4T-!/#.C•
!G->-!U#+"+!+!%7-!=1K@.@1K%3+#!c?-!=1#4?->.RS
ˆyhrŽx•†•‘’
?O#(8->+67#!L; ?O#(8->+67#4N

(lB$pA'->+!G#}g•B}•K@?+"+
9[->+[(?#42-FE(l1O+!(%3-
v2'+L'(w+1[+h%I-!@-!
B-2'+"+$)R+#%I-!@-!
)R->9<-+"+!.@1#!7;(p%
!%3'(%3-#!I(J#K@?!7%(L'9:;9<-
$D->+"+!#!7;(p%FGS%-9Œ->.@1
->'l-(%3-
v2'+L'-!/-9[->+[#%I-
!@-!#!c?-!=1B>!%VI#P'mK@?
$m->f
V%&1#47+"+-!=1#%I-!@-!#!C
!C->!%31
fE(l1O+!(%3-
h%I-!@-!#!C->!%31
n+1O+!(%3-#!c?FE(l!T-!ff
}"+!f

g:;fu+`+:1(I-
(?O-9:;9<-(7->Až#
g:;hu(?O-9:;9<-(7->Až#
(I--–1}•+6771ScVI
g:;iu-–1}g•+6771ScVI
4

g
r
4
0
2,7,7

!%VI#P'mK@?$m->f—4m.M%+:'
f
ˆ!/-Až#

r!%#\->}!?J+>%m1•
!%3'(%3-#!I(J#K@?!7%(L'9:;9<-
$7?-!%2'.L-#!T+)M->(89N->(%3-
+!O;P'79:;9<-(=+Ÿ->#\->}!?J+
>%m1•$U;-!%2'.L-
ˆy~ ¡yz‰yŽ¢rš’
v2'+L'(w+S!L-#!Z->$"?
1[+fO->(l#!,B#4m.M%+:'!^%
g2'(J+(%&1()M->$%&'9%t-F`
S![#!'8++67K@?
g`7K@?(l#!,+!?$%I#
efB€—e•
ei—e•
e…—e•
!)R->9<-.O%+"+!Ks(l#!,K@
;2'+L'#u->#4m.M%+:'hK@?
K5
w%-2'-!/-Až#KQ(l#!,+67
1T-!B>%m%#!C+!rI#P'm(?+N-
1n+F7%FGB9?(=()M->$%&'9%t-(%
P'7>L-#U#+m+"+(%&1$%&'9%t-
2'VI#.'/-KQ1G%P'7-!3>%H7
K@
yl#!,$%&'9%t-F`S![#!'8++67
+)M->(89N->(%3-K@?!%3'(%3-
#!I

+67+)M->(8
9N->(%3-K@?
!%3'(%3-#!I
>%H7!7%(L'9:;
9<-
gO->(l#!,
$%&'9%t-F`S![
#!'8++67K@?
>%H7!7%(L'9:;
9<-
v2'+L'18#
(w+.O%S!L->!%
-!R+'G%$@%
ehB€—e•B€
eiB€—e•B‚
—'G-A"+(,-!
>%"#4,B]->
KR%18#(%&1
$U#VT#42-(l#!,
#7.@1-!)F7'
gr¥()M->#!£->
F?->F?->KR%
#4[+!?@-!B+n#
#4[+#'->#O%(%&1
+=+)M->(8
#)E->]->
gr¥()M->#!£->
F?->F?->KR%
#4[+#'->B+n##4[+
!?@-!#O%(%&1+=

9<-
i!"%(8
¨-#!/-BV%2-#4T#4?->!w+#/S
x©x‰
r¥F„-$m->>!%>%"#4,#!)E->FG
U
I
 `7K@?VI#P'mFG.%3'#4?->$m->fK@h5$@%fB
#C-!#!)E->FG
U
I
—!/-Až#
!'#!/S#!Z->#%-`7K@?FG.%3'#!'()*+#u5$@%#4)R+
†|y‡|v
ˆyfrŽx•†•‘’
r%&1#47$@%+Ÿ
f2'VI#.'/-KQ1G%P'7-!3>%H7
!%3'(%3-#!I>%H7!7%(L'9:;9<-K@
+)M->(89N->(%3-+!O;P'79:;
9<-(=
hu$m->VI#P'mFG.%3'5$@%#4)R+
!”;A"+(,-!#!)E->FG
U
I
uVI#
P'm#!C->!%31!”;-2'-!/-Až#
f)M->(89N->(%3-+!O;P'718#
9:;9<-#_.3#!'/-KR%!%3'(%3-#!I
(J#K@?!7%(L'9:;9<-(=
Trình bày rõ, đúng 3 điểm.

I
KR%9:;
9<-—2'-!/-Až#K@#4m.M%+:'h
!)R->9<-#!m?.'/-(&#4m
.M%+:'h
v2'+L'(w+S!L-#!Z->$"?+67
1[+hK@#4m.M%+:'!^%2'+Z->
#!]+#C-!(%3-#45
>%R%#!%3'VC!%3'(%3-#45#4?->
FE(l1O+!(%3-B(E-K,#C-!(%3-
#45v2'+L'KsFE(l1O+!(%3-
A"+(,-!(%3-#45+6718#9:;9<-K@
-2'+"+!#C-!(%3-#45
w%f.2-$m->KsFE(l1O+!
(%3-BV!"+-!/-Až#BFo7
+!H7-I'+L-
)R->9<-+"+!(p%(E-K,(%3-
#45
?F"-!(%3-#45+679:;9<-5$m->
fK@h—2'X->!Y7+67(%3-#45
y%3-#45+679:;9<-
fb"+(,-!#!)E->FG
U
I
(G%KR%
1k%9:;9<-
gR%1k%9:;9<-#!T#!)E->FG
U
I


«->!Y7+67(%3-#45x%&'#!,1]+
(8+m-#459N->(%3--!%Q'!7;C#+67
8
r
8
9:;9<-
ˆyixŽšxŽ†y‰’0
!)R->9<-#u+Z->#!]+
U U
R I
I R
= → =
K@#!Z->$"?(:;+!C-!
.@$%&'#!]++67(,-!.'/#01v2'
+L'9`7K@?$%&'#!]+(,-!.'/#01
!”;S!"#$%&'(,-!.'/#01
y,-!.'/#01
f3#!]++67(,-!.'/#
U
I
R
=
trong đó: U đo bằng vôn (V),
I đo bằng ampe (A),
R đo bằng ôm (Ω).
h!"#$%&'(,-!.'/#
Cường độ dòng điện chạy qua dây dẫn tỉ
lệ thuận với hiệu điện thế đặt vào hai đầu
dây và tỉ lệ nghịch với điện trở của dây
ˆy~’‘Š•¤

4T-!$@;(L;(6
+"+$)R+B(–->

}ƒ(%&1•
h!"#$%&'(=.@
F7%KT#_FG
U
I
.@
V!Z->(p%(G%KR%
18#9:;9<-9?
(=V!Z->#!&-=%
#_.3#!'/-KR%
B#_.3->!,+!
KR%
}h(%&1•
~T+Œ->f
!%3'(%3-#!I
(J#K@?!7%(L'
+"+9:;9<-V!"+
-!7'B#_.3
->!,+!KR%
2-
h
ei
f
#!T

f
ei

f(%3-#45+!)7$%I##4,FG}9"-VC-#4,FG•f->'l-(%3-…
f71ScVI+=yffKZ-VI+=y…Bfh
f+Z->#n+(%3-"+(?O-9:;-G%
 !`+->!%31
fr%&1#47S!L-+!'¨-$,.C#!';I#+67+!?$@%
h!%7#!@-!+"+-!=1B1k%-!=1#42-18#$89[->+[
iyO%9%3--!=1-2'4¬1[+#%2'K@+"+$)R+#%I-!@-!BF7'(=1R%#%I-!@-!
~?O#(8->-!=1
€!?@-#!@-!S!L-$"?+"?
…'G%>%M!w+#!'$"?+"?B-2'-!/-Až#KQX#!]+B#!"%(8K@#"+
S!?->
†|y‡|v
ˆyfrŽx•
v2'+L'.RSS!=!w+#/S$"?+"?
10
10
V
A
+
-
Đoạn dây dẫn đang xét
4
3
2
1
5
6
K
#T-!!T-!+!'¨-$,$@%+67+"+$O-
#4?->.RS

?@-#!@-!$"?+"?47?(p%
-!=1(&-!/-Až#KQ->';2--!:-
>:;47F`V!"+-!7'+67+"+#4,FG
(%3-#45Ku7#C-!()*+#4?->1k%.L-
(?
!=1#4)5->+o(O%9%3-.2--!/-
9[->+[BS!:-+Z->$O-#!)VC
>!%+!žSVI#P'mK@XV%I-#!m?.'/-
+67+"+$O-#4?->-!=1
"+-!=1#%I-!@-!
U#+m#4?->-!=1(Q'#!71>%7
1n+!?J+#!c?9¬%BV%&1#47+"+!
1n++67+"+$O-#4?->-!=1
yw+VI#P'm(?(–->P';#n+
"-!:-!?@-#!@-!$m-$"?+"?
1[+7•B$•
47?(p%-!=1!?@-#!@-!-!/-Až#
+•
ˆyiršByy‡’
#!'$"?+"?
!/-Až#4–#V%-!->!%31KQ
g!7?#"+
g!"%(8!w+#/S+67-!=1
g«#!]+V_.'/#
ˆy~Š•¤
11
11
0-.O%V%I-#!]+KQ1O+!1n+-G%#%ISBF?->F?->(”!w+5.RS‚
¢r


/-9[->V%I-#!]+(”!w+(&>%m%#!C+!18#FG!%3-#)*->(E->%m-+=.%2-
P'7-#4?->#!`+#I
v2'#!C+!1Z-!w+
x©x‰yz{
yG%KR%1k%-!=1
i(%3-#45.L-.)*#+=>%"#4,…ΩBf•ΩBf…Ω>'l-(%3-18#+!%Q'…
f71ScVI+=yffKZ-VI+=y…
f+Z->#n+(%3-"+(?O-9:;-G%
 !)E->S!"S#!`+->!%31
548->#!21+!?(?O-1O+!>l1i(%3-#45—a-#)9';V!"%P'"#+!?
†|y‡|v
ˆyfrŽx•†•‘’
r%&1#47$@%+Ÿ
f
f!"#$%&'K@K%I#$%&'#!]++67
(,-!.'/#01•
f!"#$%&'K@K%I#(–->$%&'#!]+
(,-!.'/#01
)M->(89N->(%3-+!O;P'79:;9<-
#_.3#!'/-KR%!%3'(%3-#!I(J#K@?
!7%(L'9:;9<-K@#_.3->!,+!KR%
(%3-#45+671k%9:;
12
12
h!H7$@%#/Shf}x•
+m.RS+!–X.n->->!cB-2'-!/-
Až#à("-!>%"+!?(%&1
yy4?->S!L-(%3-(”!w+5.RS
‚B+!–->#7(”#T1!%&'KQ(?O-1O+!
-G%#%IS%3'+=#!&#!7;#!I!7%(%3-

ˆyh0|rš†®±yšxŠ
h4?->F(?O-1O+!>l1h
$=->(a-1n+-G%#%ISB+)M->(8
9N->(%3-+!O;P'71k%(a-+=1G%
P'7-!3-!)#!I-@?KR%+)M->(8
9N->(%3-1O+!+!C-!•
%3'(%3-#!I>%H7!7%(L'(?O-
1O+!.%2-!3-!)#!I-@?KR%!%3'
(%3-#!I>%H7!7%(L'1k%$=->(a-•
v2'+L'#4m.M%f
#!Z->$"?+"+!3#!]+}f•K@}h•
K<-(–->(G%KR%(?O-1O+!>l1h
(%3-#451n+-G%#%IS
v2'+L'+"-!:-!?@-#!@-!h
)M->(89N->(%3-K@!%3'(%3-
#!I#4?->(?O-1O+!-G%#%IS
f!R.O%V%I-#!]++Ÿ
y
f
-#y
h

f
e
h
e}f•

f
g
h

h h h



U I RU
I U I R
R U I R
= → = → =
T
f f
f h
h h
U R
I I
U R
= → =
}(++1•
"+!h
f h
f h
f h
U U
I I
R R
= → =
!7;
f f
h h
U R
U R

f y%3-#45#)E->()E->
h Z->#!]+#C-!(%3-#45#)E->
()E->+67(?O-1O+!>l1h
(%3-#451n+-G%#%IS
i=1#n#
f
-#
h
²1
#(
e
f
g
h
%m%T
f
-#
h
-2-

x
e
f
g
h
—
x

#(
e

f

L-hn+
i
ef…ªK@?e…B(w+

h
?F"-!
f
K@
h

~rI#.'/-

f
-#
h
+=
#(
e
f
g
h

ˆy~‘’Š•¤
v2'+L'+"-!:-!?@-#!@-!+:'~
±'7+:'~1548->B+!_+L-f
+Z->#n+(%Q'V!%&-(?O-1O+!1n+
-G%#%IS
)E->#`;2'+L'!?@-#!@-!

g
h
eh•ªgh•ªe~•ª
n+#!21
i
K@?(?O-1O+!#42-#!T
(%3-#45#)E->()E->

+67(?O-
1O+!1R%.@


e
fh
g
i
e~•ªgh•ªe…•ª
g

.R-!E-1k%(%3-#45
#!@-!S!L-
ˆw+$@%K@.@1$@%#/S~}x•
0-.O%V%I-#!]+KQ1O+!1n+F?->F?->(”!w+5.RS‚
¢r™
14
14



Ngày soạn: Ngày giảng: Tiết 5:

ef€ªj
h
ef•ªj
i
e…ª
f71ScVI+=yffKZ-VI+=y…
f+Z->#n+f->'l-(%3-…"+(?O-9:;-G%
 !Z->P'7$@%#/SB1548->+!?(?O-1O+!>l1i(%3-
#451n+F?->F?->K@+=#4,FG(%3-#45$D->-!7'K@$D->
f
#!T
f
i
td
R
R =

†|y‡|v
ˆyfrŽx•†•‘’
4?->(?O-1O+!>l1h$=->(a-1n+F?->F?->B!%3'
(%3-#!IK@+)M->(89N->(%3-+67(?O-1O+!+=P'7-
!3#!I-@?KR%!%3'(%3-#!IK@+)M->(89N->(%3-+"+
1O+!4s•
yyyG%KR%(?O-1O+!1n+-G%#%ISB+!–->#7(”$%I#

#(
$D->#p->+"+(%3-#45#!@-!S!L-R%(?O-1O+!
F?->F?->(%3-#45#)E->()E->+67(?O-1O+!+=$D->
#p->+"+(%3-#45#!@-!S!L-V!Z->•—x@%1R%
y

f
²²
h
—%I#!3#!]+KR%!7%(%3-#45

f
²²
h

)R->9<-#!m?.'/-h
=#!&()747-!%Q'+"+!+!]->
1%-!—-!/-Až#$pF'->
u$%&'#!]+}i•B!”;S!"#$%&'
#!@-!.M%1G%P'7-!3>%H7+)M->(8
9N->(%3-P'7+"+1O+!4sK@(%3-
#45#!@-!S!L-
)M->(89N->(%3-K@!%3'(%3-
#!I#4?->(?O-1O+!F?->F?->
T-!€f
f
²²
h
}•-#}
f
²²
h
•—}•(?+)M->(8
9N->(%3-1O+!+!C-!}•(?y
>%H7!7%(%&1Bx+Ÿ->+!C-!.@
y>%H7!7%(L'

f
f f f h
h
h h f
h


U
I R U R
U
I U R
R
= =
T
f
²²
h
-2-

f
e
h
—
f h
h f
I R
I R
=
}i•—4?->(?O-
1O+!F?->F?->+)M->(89N->(%3-

²²
h
—e
f
g
h
—
f h
f h
AB
td
U U U
R R R
= +
1@
f h
f h
f f f
AB
td
U U U
R R R
= = → = +
}~•
16
16
M
+Z->#!]+}~•%I-!@-!V%&1
#47—rI#.'/-
#!Z->$"?>)M%#7#!)M->9Œ->+"+

ef€ªj
h
ef•ª
gL-hn+
i
K@?e…B
i
e…ªB
(w+
h
e•
g?F"-!
f
KR%
h

irI#.'/-
ˆy~’‘Š•¤
v2'+L'S!"#$%&'#!@-!.M%
1G%P'7-!3>%H7BB#4?->
(?O-1O+!F?->F?->
v2'+L'#!m?.'/--!=1-!^
#4m.M%+:'~
v2'+L'+"-!:-!?@-#!@-!+:'
€
1548->
g4?->(?O-1O+!+=i(%3-#45
1n+F?->F?->#!T(%3-#45#)E->
()E->
f h i

fh
fh f h
f f f f f f
f€
i• i• f€
R
R R R
= + = + = → = Ω
gr!%1n+#!21(%3-#45
i
#!T(%3-#45
#)E->()E->

+67(?O-1O+!1R%
.@
fh i
f f f f f i f
f•
f€ i• i• f•
AC
AC
R
R R R
= + = + = = ⇒ =


-!^!E-1k%(%3-#45#!@-!S!L-
@1$@%#/S€}x•
0-.O%V%I-#!]+$@%hB~B€
¢r™

yy
4c?$m->S![+"+$)R++!'->(&>%m%$@%#/S(%3-
ˆyhµx’f
w%f(w+(Q$@%$@%f
w%f#=1#n#(Q$@%
v2'+L'+"-!:->%m%$@%#/Sf
47-!"S
)R->9<-
g!?$%I#
f
K@
h
()*+1n+KR%
-!7'-!)#!I-@?•1ScVIBKZ-
VI(?-!H->(O%.)*->-@?#4?->
1O+!(%3-•
=1#n#
f
e€ªj
K
e…j

e•B€
7•
#9
e•j
h
e•
x@%>%m%
!:-#C+!1O+!(%3-

g/-9[->+Z->#!]+-@?(&#C-!
(%3-#45#)E->()E->
#9
K@
h
•
—!7;FG#C-!
#9
—
h

v2'+L'-2'+"+!>%m%V!"+B
+!£->!O-C-!
f
F7'(=#C-!
h

—
h
K@#C-!
#9
e
f
g
h

y%3-#45#)E->()E->+67(?O-1O+!
x.@fhª
$•T
f

f h
h f
²²
I R
R R
I R
→ = →
"+!#C-!
h
KR%

f
j
f
(”$%I#j
h
e
f

?J+(%#C-!
x

f h h f
h
h
fh h•
fBƒ i
f f f f f f
f i f f
h•

f
efBhj

efBƒ
7• 
x
e•j$•
h
e•
x@%>%m%
7• }•-#
f
—
f
e
f
efBh
}• -#}
f
²²
h
•—

e
x
efBƒ
u+Z->#!]+
f f f
f h f h
  fBhf• fh} •

U V
R
R A
= = = Ω
/;(%3-#45
h
$D->h•ª
ˆy~µx’i
)E->#`!)R->9<->%m%$@%#/S
i
+!H7$@%K@('747$%&'(%&1
+!U1+!?#u->+:'v2'+L'(p%
$@%+!?-!7'(&+!U1(%&1+!?+"+
$O-#4?->-!=1
)'X+"++"+!#C-!V!"+-!7'B-I'
(–->K<-+!?(%&1#G%(7
=1#n#}f(%&1•

f
ef€ªj
h
e
i
ei•ªj
x
efh
7•
x
e•$•
f

}f(%&1•
(%3-#45+67(?O-1O+!x.@i•ª
19
19
}•B€(%&1•
$• S9[->+Z->#!]+(,-!.'/#
01
f
fh
•B~
i•
•B~
AB
AB
AB
AB
UU V
I I A
R R
I I A
= → = = =
Ω
= =

}fB€(%&1•
f f f
 •B~f€ …U I R V= = =
}f(%&1•
h i f
fh … …

x@%hK/-9[->KR%(?O-1O+!>l1h(%3-#451n+F?->F?->x@%iK/-9[->
+!?(?O-1O+!!k-!*S)'X+"+!#C-!(%3-#45#)E->()E->KR%1O+!!k-
!*S
Q-!@.@1.@%#/S…}x•
¢r™



Ngày soạn:
Ngày giảng: Tiết 7:
SỰ PHỤ THUỘC CỦA ĐIỆN TRỞ VÀO CHIỀU DÀI DÂY DẪN.
 
f r%I-#!]+
2'()*+(%3-#45+679:;9<-S![#!'8+K@?+!%Q'9@%B#%I#9%3-K@K/#.%3'
.@19:;9<-
x%I#+"+!A"+(,-!F`S![#!'8++67(%3-#45K@?f#4?->+"+;I'#G}+!%Q'9@%B
#%I#9%3-BK/#.%3'.@19:;9<-•
20
20
';.'/-K@#%I-!@-!V%&1#47F`S![#!'8++67(%3-#459:;9<-K@?+!%Q'
9@%
2'()*+(%3-#45+67+"+9:;9<-+=+Œ->#%I#9%3-K@()*+.@1#u+Œ->18#
K/#.%3'#!T#_.3KR%+!%Q'9@%+679:;
hrY-\->n+1O+!(%3-K@Fo9[->9[->+[(?(&(?(%3-#45+679:;9<-
i!"%(84'->#!`+B+=#%-!#!L-!*S#"+#4?->!?O#(8->-!=1
xyz{|v
yG%KR%1k%-!=1
f->'l-(%3-if+Z->#n+f71ScVI+=y.@f
fKZ-VI+=y.@…i(%3-#45
f

S!L-•
hsFE(l1O+!(%3-Fo9[->KZ-VIK@
71ScVI(&(?(%3-#45+6718#9:;9<-
("-!>%"+!?(%&1h
yy!–->#7$%I#KR%1k%9:;9<-#!T
.@V!Z->(p%/;(%3-#451k%9:;9<-
S![#!'8+-!)#!I-@?K@?$m-#!:-9:;
9<-(=•—x@%1R%
x@%…hS!L-7•
7• Th+"+!1n+(Q'()*+1n+
K@?+Œ->18#!%3'(%3-#!I
e…

f
y%3-#45#)E->()E->+67(?O-
1O+!.@
#9 f
f
…
 f€
•B~
td
U V
R
I A
= → = = Ω

h
y%3-#45#)E->()E->+67(?O-
1O+!.@

= +
= +
s(–->FE(l1O+!(%3-B+!_4¬
+!G#-G%KZ-VIB71ScVI}€(%&1•
ˆyh•Žy™“œv•‡›vš
‘•
v2'+L'P'7-F"#+"+(?O-9:;9<-5
b"+(,-!F`S![#!'8++67(%3-#45
21
21
!T-!‚f+!?$%I#+!–->V!"+-!7'5;I'
#G-@?•y%3-#45+67+"+9:;9<--@;.%3'
+=-!)-!7'V!Z->•
—vI'#G-@?+=#!&>:;m-!!)5->(I-
#45+679:;9<-
v2'+L'#!m?.'/--!=1(Q47S!)E->"-
V%&1#47F`S![#!'8++67(%3-#459:;9<-
K@?+!%Q'9@%9:;9<-
v2'+L'()747S!)E->"-#p->P'"#
(&+=#!&V%&1#47F`S![#!'8++67(%3-
#45K@?f#4?->i;I'#G+67$m-#!:-9:;
9<-
9:;9<-K@?18##4?->-!H->;I'#G
V!"+-!7'
T-!‚f"+9:;9<-V!"+-!7'
g!%Q'9@%9:;
g%I#9%3-9:;
g!U#.%3'.@19:;9<-
ˆyiby‰˜‡y™“¤
œv•

=
`F`S!'8++67(%3-#45K@?
+!%Q'9@%9:;9<-
f`V%I-+"+!.@1
h!C->!%31V%&1#47
irI#.'/-
y%3-#45+67+"+9:;9<-+=+Œ->#%I#
9%3-K@()*+.@1#u+Œ->18#.?O%
K/#.%3'#!T#_.3#!'/-KR%+!%Q'9@%
+671k%9:;
ˆy~’‘Š•¤
v2'+L'+"-!:-!?@-#!@-!h
)R->9<-#!m?.'/-+:'h
)E->#`KR%+:'~
h!%Q'9@%9:;+@->.R-}.+@->
.R-•—y%3-#45+67(?O-1O+!+@->
.R-}+@->.R-•I'>%Hy}•
V!Z->(p%—)M->(89N->(%3-
+!O;P'7(?O-1O+!+@->-!^}
+@->-!^•—ya-F"->+@->;I'
~Ty(J#K@?h(L'9:;V!Z->
(p%-2-#_.3->!,+!KR%9?
f h h f
•h€ •h€I I R R= → =
!7;
f h
~R R=

22
22

h(%3-#459:;P'U-+Œ->.?O%

f h h f f h
j ~ } •i j •… •l l S S mm mm= = Φ = Φ =
f->'l-(%3-f+!%Q'…f+Z->#n+
f71ScVI+=y.@fK@y••h
fKZ-VI+=y.@…K@y•f"+(?O-9:;-G%
 !'#!/S#!Z->#%-—9`(?"-—F';.'/-9%t-9,+!#u
#4)M->!*S+!'->+!?18##4)M->!*S4%2->—r%&1#47$D->#!`+->!%31—
r!£->(,-!#C-!(–->(n-
†|y‡|v
ˆyfrŽx•†•‘’
f4?->(?O-1O+!>l1h(%3-#45
1n+F?->F?->ByK@+)M->(8
9N->(%3-+67(?O-1O+!+=P'7-!3
#!I-@?KR%yK@+)M->(89N->
(%3-+67+"+1O+!4s•%I#+Z->
#!]+#C-!(%3-#45#)E->()E->+67
f4?->(?O-1O+!>l1
23
23
(?O-1O+!(=
h'G-A"+(,-!1G%P'7-!3>%H7
(%3-#45K@?+!%Q'9@%9:;9<-#!T
S!m%(?(%3-#45+679:;9<--!)#!I
-@?•
isFE(l1O+!(%3-V%&1#47F`
S![#!'8++67(%3-#459:;9<-K@?
+!%Q'9@%9:;
w%-!/-Až#+:'#4m.M%+67$O-B

u+:'!^%f—`(?"-F`S![
#!'8++67K@?P'7+:'h
`(?"-F`S![#!'8++67(%3-#45
K@?#%I#9%3-9:;9<-
f
h i
j
h i
R R
R R= =
h4)M->!*S!7%9:;9<-+=+Œ->
+!%Q'9@%K@+Œ->()*+.@1#u+Œ->
18#.?O%K/#.%3'B#!T(%3-#45+67
+!–->#_.3->!,+!KR%#%I#9%3-9:;
ˆyi™rŽ˜y
sFE(l1O+!(%3-V%&1#47—2'
9[->+[+L-#!%I#(&.@1B+"+
$)R+#%I-!@-!
v2'+L'.@1V%&1#47#!c?
-!=1(&!?@-#!@-!$m->f#4hi
#!'VI#P'm+67+"+
-!=1—)R->9<-#!m?.'/-+!'->
+m.RS
v2'+L'F?F"-!KR%9`(?"-(&4–#
47VI#.'/-
v2'+L'(w+;2'+L'S!L-i
!/-Až#C-!#_FG
h
h h
h

h

 
h ~
d d
S R
π
π π
 
= = =
 ÷
 
_FG
h
h
h
h h
h
h
f
f f

~

~
d
S d
d
S d
π

h
f h
f h
h
h f
…
i i
h
R S
mm
R R
R S mm
→ = = = → =
y%3-#45+679:;#!]-!U#>USi.L-
(%3-#45+679:;9<-#!]!7%
x@%ƒh
!%Q'9@%.R->US~#!T(%3-#45>US
~.L-B#%I#9%3-.R->USh#!T(%3-#45
-!^!E-h.L-BK/;
f h
hR R=

€"+!f:;9<-#!]!7%+=
+!%Q'9@%
f
h
h
l
l =
-2-+=(%3-#45-!^