Chapter 3 Electromagnetism
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Transcript of Chapter 3 Electromagnetism
-
Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
44
Electromagnetism
3.1 Analysing the Magnetic Effect of a Currentcarrying Conductor
Magnetic Effect of a Currentcarrying Conductor
(a) Electric bell
(b) Magnetic relay
switch
current
electromagnet
pulled byelectromagnet
spring
contact point
contact screwarmature
hammer
gong
+
battery
output
input
contact switch
fulcrum
armature
electromagnet
pulled by electromagnet
+
-
Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
45
Electromagnetism
3.1 Analysing the Magnetic Effect of a Current-carrying Conductor
Magnetic Field
S N
N N S S
N S
S
Nbehaveslikea bigmagnet
earth's magnetic field
-
Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
46
Electromagnetism
3.1 Analysing the Magnetic Effect of a Current-carrying Conductor
Magnetic Field By Current-carrying Conductors
(a) Straight wire
(b) Coil
(c) Solenoid
I Icurrent
+ +
X X
+
X
+I I I I
+
-
Electric current is coming out
direction of magnetic field is anti-clockwise
SN
I
+
Umagnetic field
Battery
current
Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
47
Electromagnetism
3.1 Analysing the Magnetic Effect of a Current-carrying Conductor
Maxwells Right Hand Rule
I
Direction ofmagnetic field
Direction ofcurrent
I
Direction ofcurrent
I I
Direction ofmagnetic field
N
X
X Electric current is going in
direction of magnetic field is clockwise
UN
I
S
+
Battery
current
Direction ofmagnetic field
-
Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
48
Electromagnetism
3.2 Understanding the Force on a Current-carrying Conductor ina Magnetic Field
Force on a Current-carrying Conductor in a Magnetic Field
Flemings left hand rule
Force in a lastic (catapult) field
Generating force in a magnetic field
uniform fieldfrom magnet
concentric fieldby electric current
stretching of magneticfield to produce a force
ForceXX+ =
south polemagnadur magnet
metal rod taped
+
wooden block
north pole
light conductor
MI
I
I
F
M
F
I
F (force)
I (current)M (magnetic field)
-
permanent magnet
wire coil
carbonbrush
Direction of turning
commutator
rheostat
battery
SN
+
Direction of turning
B
permanent magnet
wirecoil
rotating slip-rings
A.C.
carbon brushes
NSA
Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
49
Electromagnetism
3.2 Understanding the Force on a Current-carrying Conductor ina Magnetic Field
Principle of Motor
A.C. MOTOR
D.C. MOTOR
-
FARADAYS LAW
Longman Project! Overhead Transparencies Physics Form
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Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
50
Electromagnetism
3.3 Analysing Electromagnetic Induction
Electromagnetic Induction
Cutting the magnetic flux produces electric current
Flemings right hand rule
magnadur magnet
metal rod
GI
Movement of rod
wire
galvanometerInduced current
S N
M
I
FMagnetic field
Motion
Electric current
-
Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
51
Electromagnetism
3.3 Analysing Electromagnetic Induction
Electromagnetic Induction
N
solenoidpush in
magnet
GI Induced
current
galvanometer
N S
Inducedcurrent
galvanometer
S
pull out
magnet
GI
N S
LENZS LAW
Same magnetic pole produced generatesa repulsive force
Opposite magnetic pole produced generates anattractive force
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Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
52
Electromagnetism
3.3 Analysing Electromagnetic Induction
Current Generator
A.C. GENERATOR
Induced e.m.f.
Number ofrevolution
O 34
14
12
1
Turning
B
strongmagnet
slip-rings
Load
carbon brushes
N
SA
Q
P
wirecoil
-
Longman Project! Overhead Transparencies Physics Form
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Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
53
Electromagnetism
3.3 Analysing Electromagnetic Induction
Current Generator
D.C. GENERATOR
S
BN
QP
I
AN
strongmagnet
carbonbrush
Turning
commutator+
wirecoil
directcurrent
Induced e.m.f.
Number ofrevolution O 1
434
12
1
Load-
+
-
Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
54
Electromagnetism
3.4 Analysing Transformers3.5 Understanding the Generation and
Transmission of Electricity
Transformer
Symbol
Vp primary voltageVs secondary voltageNp number of turns in
primary coilNs number of turns in
secondary coilIp primary currentIs secondary current
Principle of transformer
1 Voltage V Number of turns N
= =
2 With no power loss P = IpVp = IsVs
3 Efficiency = 100%
= 100%VsIsVpIp
power outputpower input
IpIs
NsNp
VsVp
laminated soft-iron
secondarycoil
primarycoil
Np Ns
A.C. input A.C. output
Vp Vs
IpIs200
800
primary secondary
Structure
-
Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
55
Electromagnetism
3.4 Analysing Transformers3.5 Understanding the Generation and
Transmission of Electricity
Type of transformer
Vs > VpNs > Np
VsVp NsNp
Vs < VpNs < Np
VsVp NsNp
step-down transformer
11 kV 480 V 240 VLocal stations
11 kV
11 kV
240 V Houses
33 kV
25 kV
11 kVstep-downtransformer
step-uptransformer
powerstation
132 kV
33 kV
power cableat 33 kV
132 kV
Step-up transformer Step-down transformer
National grid transmission system
-
Longman Project! Overhead Transparencies Physics Form
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Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
56
Electromagnetism
3.4 Analysing Transformers3.5 Understanding the Generation and
Transmission of Electricity
Moving Coil Galvanometer (for D.C. only)
N S
Radial field Advantages
Sensitive Linear scale Can be adapted to become an
ammeter or a voltmeter
AI I
B
R
rIo Io
(I- Io)
I- Io I- Ioshunt
shunt
R = =VGIor
As an ammeter
A BRIo Io
Io Io
VR VG
R = V-VGV-Ior=
V
multiplier
r
As a voltmeter
r = internal resistance of galvanometerIo = maximum current for full-scale deflectionVG = maximum p.d. across galvanometer
pointer
rectangular coil
semicircular magnet
linear scalespring
springsoft-iron core
I
D.C.
SN
S
-
Longman Project! Overhead Transparencies Physics Form
5
Pearson Malaysia Sdn.Bhd. 2007
CHAPTER
333
57
Electromagnetism
3.4 Analysing Transformers3.5 Understanding the Generation and
Transmission of Electricity
Instruments for Measuring Electric Current (for D.C. and A.C.)
pointernon-linear scale
silk thread
zero adjustor
adjusting screwplatinumwire
shunt
A B
+ - II
pointer
permanentiron plate
terminal T1 terminal T2
bearing
bearing
solenoid
movable iron plate
fine spring
non-linear scale
shaft
Hot-wire meter
Moving-iron meter
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