Appendix D

Component Schematic
Symbols
Voltage and Current Sources

⫹ Individual voltaic cell

(longer line indicates
⫺ AC voltage source
the positive electrode)

⫹
Standard symbol for a
⫺ dc voltage source
Current source
(solid arrow represents
conventional current flow)

⫹
Variable dc voltage source
⫺

Current source
(dashed arrow represents
electron flow)

Ground Symbols
Earth ground Chassis ground Common ground

Connections
Connection
No connection

No connection

Dot indicates connection

1101

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 Resistors

Variable resistor
Fixed resistor (generic symbol)
(2 terminals)

Rheostat
Potentiometer (2 terminals)
(3 terminals) R decreases as
wiper is moved up

(No connection)

(No connection)

Rheostat Rheostat
(2 terminals) (2 terminals)
R decreases as R increases as
wiper is moved up wiper is moved up

Rheostat
(2 terminals)
R increases as T Thermistor
wiper is moved up

Capacitors

Fixed capacitor Ganged capacitors

⫹
Variable capacitor Electrolytic capacitor
⫺

⫹
Variable capacitor
Electrolytic capacitor
⫺

1102 Appendix D

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 Inductors (Coils)

Fixed inductor Variable inductor Variable inductor

(air core) (adjustable powdered (generic symbol)
iron or ferrite slug)

Fixed inductor Tapped inductor

(iron core)

Transformers

Primary Secondary Air-core transformer

Primary Secondary Iron-core transformer

Secondary
Center Iron-core transformer
Primary
tap with secondary center tap

Secondary 1

Iron-core transformer
Primary with multiple secondaries

Secondary 2

Primary Autotransformer
Secondary

Component Schematic Symbols 1103

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 Switches
SPST
DPDT

SPDT

Normally open (NO)

push-button switch

DPST

Normally closed (NC)

push-button switch

Protective Devices
Fuse

Circuit breaker

Relays
Normally open (NO)
or
relay contacts
Relay coil

Normally closed (NC)

or
relay contacts

Relay coil

Lamp

Incandescent lamp

1104 Appendix D

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 Test Instruments

V or V Voltmeter ⍀ or ⍀ Ohmmeter

A or A Ammeter

Diodes
Anode Cathode Cathode
Rectifier diode

Zener diode
Anode Cathode
Light-emitting diode (LED)
Anode

Transistors
Collector Drain

n-channel JFET
Base npn transistor Gate (asymmetrical)

Source
Emitter

Drain
Collector

p-channel JFET
Gate
(symmetrical)

Base pnp transistor

Source

Emitter Drain

Drain n-channel
Gate D-MOSFET

n-channel JFET
Gate
(symmetrical) Source

Source

Component Schematic Symbols 1105

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 Drain Drain

p-channel p-channel
Gate D-MOSFET Gate E-MOSFET

Source Source

Drain

n-channel
Gate E-MOSFET

Source

Thyristors
MT2

Diac Triac
Gate
MT1

Anode B2

Silicon-controlled
rectifier (SCR) E Unijunction transistor
Gate (UJT)
Cathode

B1

Operational Amplifier (Op Amp)

Noninverting
⫹
input Output
Op amp
Inverting
⫺
input

1106 Appendix D

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