21 electromagnetic induction. induction experimental
TRANSCRIPT
21 Electromagnetic Induction
Induction Experimental
Magnetic Flux
cosABB
Units: Weber (Wb) 1 Wb = 1T.m2
Faraday’s Law of InductionThe magnitude of the induced emf in a circuit equals the absolute value of the time rate of change of the magnetic flux through the circuit:
tB
for 1 turn or
for N turnst
N B
Generator
tBABAB coscos tAt
B sin
Lenz’s Law: Against the change
The direction of the any magnetically induced current or emf is such as to oppose the direction of the phenomenon causing it.
Lenz’s Law: Example
Motional Electromotive Force
Blvt
tBLv
B
B
“-”sign: Lenz’s LawRecall Lorentz force on the moving part
I ?
Eddy’s Currents
Application: Damping
Application: Speedometer
Mutual Inductance
t
iM
tN
iMNiN
tN
B
BB
B
121
222
12122122
222
or
t
iM
tN B
2
122
111
Similarly,
Define mutual inductance, M,
and t
iM
t
iM
i
N
i
NMMM BB
21
12
2
11
1
222112
Self-Inductance
INL
t
IL
tN
B
B
Unit 1V.s/A = 1 Henry (H)
Examples: Solenoid and Toroid
Transformers
2121
1
222211
1
2
1
2
2211
)/(
/
NN
RR
I
V
RVIVIVI
N
N
tN
tN
eff
BB
and
For an ideal transformer
Transformer & Eddy Current
Magnetic Field Energy
Energy per unit volume (using solenoid)
0
2
2
2
2
1
B
u
LIU
ILItPU
It
ILVIP
B
R-L Circuit
time
/1)( teR
tI
= L/R, time constant
L-C Circuit
Summary: Electromagnetic Induction & Faraday’s Law
Summary: Lenz’s Law
Summary: Motional EMF
Summary: Eddy’s Currents
Summary: Inductance
Summary: Transformers
Summary: Magnetic Energy
0
2
2
2
2
1
B
u
LIU
ILItPU
It
ILVIP
B
Summary: R-L & R-C Circuits
HomeworkCh21: 1, 4, 12, 16, 21, 25, 27, 32, 40, 45, 52.
P9-Faraday’s Law
P16&17 Lenz’s law
P21&25-Motional emf
P27-Mutual Inductance
2
11
1
22
i
N
i
NM BB
P32-Self-Inductance
INL
t
IL
tN
B
B
P40-Transformer
212
1
2
1
2
)/( NN
RR
N
N
V
V
eff
P45-Magnetic Energy
Voltmeter Construction
d’
V’
gssg
sgsgg
RKd
VRRRkdV
RRKdRRIV
'
')(''
)()(
or
If the V-meter required for maximum V’ (full scale) then
Ammeter Construction
d’
Ig
mcm
cm
divdivA
divdivA
or
or
5.2~10721
101.8
537.0~50101.075.0
8050101.0
'
'
'
6
24
3
3
max
max
-shsh
g
sh
ggshshshgg
shshg
.
RARLength
AKdI
RKd
I
RIRRIRI
IKdIIII