section 17.2 generator

8/14/2019 Section 17.2 Generator

1/19

Manhattan Press (H.K.) Ltd. 1

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



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no current

Plane of coil is

vertical

no field lines

cut

no current

induced




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After passing

vertical position

inducedcurrent


current flows in

directionTRQP

direction

reversed



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no current

Plane of coil isvertical

no field lines

cut no current

induced

After passingvertical position

direction ofI

reversed


principle of

a.c. generator



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external

circuit

carbon

brush

slip rings

rotation current

is induced

Simple a.c. generator



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Simple a.c. generator


Induced current

No. of

revolutions

positions

of coil

one complete

cycle


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Simple d.c. generator


Expt. 17C

Generatorgalvanometer

d.c. generator
http://movie/Expt%2017C/17C.avi


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commutator

carbonbrush

rotation

current

is induced



reverse

connections of

coil with externalcircuit every half

turn

d.c.


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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


(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


output terminals

cylindrical

magnet (rotor)

coil

U-shaped

soft-iron

core

axle

driving

wheel

provides electrical energy toheadlamp


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Bicycle alternator


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



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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


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


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



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To section 17.3
http://e-ch17_03.ppt/http://e-ch17_03.ppt/

section 17.2 generator

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