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Section 17.2Section 17.2
GeneratorGenerator
Section 17.2Section 17.2
GeneratorGenerator
Simple a.c. generatorSimple a.c. generator
Coil moving in magnetic fieldCoil moving in magnetic field
Simple d.c. generatorSimple d.c. generator
Bicycle alternatorBicycle alternator
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Generator
17.2 Generator (SB p. 154)
generator motor operate in
opposite manner
a.c. generator
(alternator)
d.c. generator
(d.c. dynamo)
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maximuminduced
current
current flows in
directionPQRT
Plane of coil is
horizontal
highest rateof cutting
magnetic field
lines
Coil moving in magnetic field
17.2 Generator (SB p. 155)
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no current
Plane of coil is
vertical
no field lines
cut
no current
induced
17.2 Generator (SB p. 155)
Coil moving in magnetic field
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After passing
vertical position
inducedcurrent
17.2 Generator (SB p. 155)
current flows in
directionTRQP
direction
reversed
Coil moving in magnetic field
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no current
Plane of coil isvertical
no field lines
cut no current
induced
After passingvertical position
direction ofI
reversed
17.2 Generator (SB p. 155)
principle of
a.c. generator
Coil moving in magnetic field
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external
circuit
carbon
brush
slip rings
rotation current
is induced
Simple a.c. generator
17.2 Generator (SB p. 156)
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Simple a.c. generator
17.2 Generator (SB p. 157)
Induced current
No. of
revolutions
positions
of coil
one complete
cycle
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Simple d.c. generator
17.2 Generator (SB p. 157)
Expt. 17C
Generatorgalvanometer
d.c. generator
http://movie/Expt%2017C/17C.avi8/14/2019 Section 17.2 Generator
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commutator
carbonbrush
rotation
current
is induced
Simple d.c. generator
17.2 Generator (SB p. 157)
reverse
connections of
coil with externalcircuit every half
turn
d.c.
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Simple d.c. generator
17.2 Generator (SB p. 158)
one complete
cycle
Induced current
No. of
revolutions
positions
of coil and
commutator
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Induced voltage at generatorby
Factors affecting the magnitude of induced
voltage
17.2 Generator (SB p. 158)
(1) rotate coil at higherspeed
(2)no. of turns of coil
(3) wind coil on soft-iron core
(4) use strongermagnet
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Bicycle alternator
17.2 Generator (SB p. 159)
output terminals
cylindrical
magnet (rotor)
coil
U-shaped
soft-iron
core
axle
driving
wheel
provides electrical energy toheadlamp
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Bicycle alternator
17.2 Generator (SB p. 159)
output terminals
cylindrical
magnet (rotor)
coil
U-shaped
soft-ironcore
axle
drivingwheel when wheel rotates
rotor rotates
coil experiences changing field
induced a.c.
chemical energy electrical energy light & heat
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Induced voltage of bicycle alternator
alternating
Bicycle alternator
17.2 Generator (SB p. 159)
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Example 3:Example 3:If a cyclist pedals a bicycle at a higher speed, explain what
would be the changes in(a) the induced voltage in the alternator,
(b) the induced current in the alternator, and
(c) the power of the headlamp.
Solut
ion
17.2 Generator (SB p. 160)
The induced voltage would be increased as the coil inside
the alternator experiences a greater rate of change of the
magnetic field.
The power also increases since P= VI.
The induced current increases since I= , I increases with V
when R remains unchanged.R
V
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Class Practice 2:Class Practice 2:The graph of output voltage against time for an a.c.
generator is shown.
(a) Find the peak voltage, period
and frequency of the output
voltage.Peak voltage = ___________
Period = ________________
Frequency = _____________
Answer
17.2 Generator (SB p. 160)
Ans
wer
Ans
wer
5 V
0.02 s
Hz5002.0
1=
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Class Practice 2: (Cont)Class Practice 2: (Cont)(b) Draw the new graph when the number of turns of the
coil is trebled.
Ans
wer
17.2 Generator (SB p. 160)
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To section 17.3
http://e-ch17_03.ppt/http://e-ch17_03.ppt/