potentiometer galvanometer kirchhoff law electromotive force d’arsonval galvanometer kirchhoff...

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