potentiometer galvanometer kirchhoff law electromotive force d’arsonval galvanometer kirchhoff...
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Potentiometer Galvanometer Kirchhoff Law
Electromotive force
D’Arsonval Galvanometer
Kirchhoff Current and Voltage Law
Potentiometer
a
Ib
I
R
I
Ir
-
+
IrVab
直流電源 D+ -
待測電池F
已知電池E
G
A B
C
R
直流電源 D+ -
待測電池F
已知電池E
G
A B
C
R
Rp
直流電源
rR
VVIrV
p
11
)(1
pR
r
V
'AC
AC
E
F εε
D’Arsonval Galvanometer
INAB
φκ
The angle of deflection of the pointer is directly proportional to the current in the loop The deflection also depends on the design of the meter
τm =μB, μ=NIA magnetic dipole moment
τs=-κψ, κis the tensional spring constant
τm+τs=0
Ammeter/Voltmeter
the ammeter should have zero resistance so the current being measured is not altered
the voltmeter should have infinite resistance so that no current would pass through it
Multimeter
RRR
IRR
RRRI
c
cc
c
0
0
0
)(
I
IIRRRR
IR cc
c
))(( 00
0
)50(RR
AIc
c
x
0
y
Ro
R
Ic
RcI
Resistance
顏色 銀 Silver金 Gold
黑 Black
棕Brown 紅 Red
橙Orange
黃Yellow
綠 Green藍 Blue
紫Violet
灰 Gray白
White無色
數值 -2 -1 0 1 2 3 4 5 6 7 8 9
誤差 ±10% ±5% ±20%
Kirchhoff’s Rules
• Junction Rule:
Iin = Iout
• Loop Rule:
closedloop
0V Loop
Resistors in Series and Parallel
nRRRR
1...
111
21
nRRRRR 321
Wheatstone Bridge
G
A
B
3211 RIRI
4221 RIRI
4
3
2
1
R
R
R
R
1R 2R
3R 4R
V