find the resistance if currents flow from (a) b to a, (b) c to d
DESCRIPTION
EXAMPLE 27.1: A copper wire carries a current of 10 A. It has a cross-sectional area of 0.05 cm 2 . Estimate the drift velocity of the electrons. - PowerPoint PPT PresentationTRANSCRIPT
EXAMPLE 27.1: A copper wire carries a current of 10 A. It has a cross-sectional area of 0.05 cm2. Estimate the drift velocity of the electrons.
smmatoms
mA
ne
J
mAm
AJ
matoms
molkg
molatomsmkgn
molkgMmkgcmgcopperForM
N
V
Nn(m/M)NN
M
m
N
N
AA
A
/105.1)C/electron10)(1.6 /105.8(
/102v
,vnqJ ,/102)105(
10
)(Cu /105.8
./105.63
.)/1002.6)(3/109.8(
./105.63 /109.8/9.8,
m/V i) from (
atoms) ofdensity number (the N/Vn density) (mass m/V (i)
4
19-328
26
d
d
26
26
328
3
233
3333
EXAMPLE 27.2: The radius of #8 copper wire is 1.63 mm. A potential difference of 60 V is applied across a 20-m length of this wire. Find: (a) its resistance; (b) the current; (c) the electric field.
mVmVlVEc
AVRVIb
m
mm
A
lR
ma
/320/60/)(
150004.0/60/)(
0.04
)1063.1)(14.3(
)20)(107.1(
rA ,107.1)(
23
8
28
Find the resistance if currents flow from (a) B to A, (b) C to D
)ln(2R
,ln2
)2
(
11
,)
2(
)ln(22
2
total
ba
t
b
at
r
tdr
dRR
tdr
r
dA
ldR
b
a
tr
dr
trtdr
A
drR
a
btotal
a
b
EXAMPLE 27.3: The heating element of a space heater is rated at 1000 W when operating at 120 V. (a) What is the current through it under normal conditions? (b) What would its power consumption be if the potential difference drops to 110 V?
WV
R
P
VR
I
b
AV
W
V
PI
a
8404.14
)110(VP
4.14
conditions operating newunder changenot willresistance ts
)(
33.8120
1000
)(
22
2
DISCUSSIONS
• RQ- ohm’s law
Exercises of chapter 27
• Questions:7,8,13
• Exercises:3,8,13,34,42
• Problem:2,4,6,