INTERMEDIATE LESSON 5logomidi2.gif

             
LEARNING  OBJECTIVES and NOTES
Note: The circuit symbols shown in the table below will be used and candidates will be expected to recognise them.

Circuit Symbols
You should be able to recognise each of these symbols used in electronic circuits.



Description Unit Symbol Description Unit Symbol
Resistor general Ohm Ω Symbol_resistor.gif Battery Volt Symbol_battery.gif
Resistor Variable (This has 2 terminals and acts as a resistor whose value can be varied. Ohm Ω Symbol_resistor_variable.gif Fuse Amp Symbol_fuse.gif
Resistor Pre-set Ohm Ω Symbol_resistor_preset.gif Semiconductor diode
Symbol_diode.gif
Resistor Potentiometer (This has 3 terminals. The centre taps off a voltage between the voltage of the two end terminals) Ohm Ω Symbol_resistor_potentiometer.gif Light emitting diode (LED)
Symbol_diode_led.gif
Capacitor general Farad Symbol_capacitor_general.gif Variable capacitance diode
Symbol_capacitance_diode.gif
Capacitor Polarised Farad Symbol_capacitor_polarised.gif Transistor (npn)Note that the circle is
optional.
Symbol_transistor_npn.gif
Variable capacitor
 Farad Symbol_variable_capacitor.gif Field effect transistor
(FET)
Symbol_transistor_fieldeffect.gif
Inductor general Henry Symbol_inductor_general.gif Antenna
Symbol_antenna.gif
Inductor Iron cored Henry Symbol_inductor_ironcored.gif Earth
Symbol_earth.gif
Transformer
Symbol_inductor_transformer.gif Chassis
Symbol_chasis.gif
Lamp
 (Watt) Symbol_lamp.gif Crystal Hertz Symbol_crystal.gif
Switch s.p.s.t.
Symbol_switch_spst.gif Microphone
Symbol_microphone2.gif
Switch d.p.s.t.
Symbol_switch_dpst.gif Loudspeaker
Symbol_loudspeaker.gif
Cell Volt Symbol_cell.gif Earphone
Symbol_microphone.gif



Units of measurement and multiple/sub-multiple prefixes
3a.1 Recall the units and abbreviations for potential difference, current, power, resistance, capacitance, inductance and frequency. Understand the prefixes pico, nano, micro, milli, kilo, Mega and Giga.
The units you need to learn are shown in the table opposite.

Base Unit
Potential difference Volt (V)
Current Amp (A)
Power Watt (A)
Resistance Ohm (Ω)
Capacitance Farad (F)
Inductance Henry (H)
Frequency Hertz (H)

Some units are too small or too large to show in the basic unit. To make them more readable they are given prefixes which tell you how large or small they are.

It is easier to read numbers if they are written in what is called Scientific Notation.

A 2.5 billion watts could be written as:
2500000000

or in Scientific Notation. 2.5 x 109

The 109 shows how many numbers come after the decimal point.

In scientific notation 1 pico Farad is written  as:

1.0 x 10-12
The - sign shows it is smaller than 1
S.N
 Prefixes
 Volts
 Amps
 Watt Ohm
 Farad
 Henry
 Hertz
109 Giga
 a billion Volts
 a billion Amps a billion Watts
 a billion Ohms a billion Farads
 a billion Henry a billion Hertz
106 Mega
 a million Volts a million Amps a million Watts a million Ohms a million Farads a million Henry a million Hertz
103
 kilo
 a thousand Volts a thousand Amps a thousand Watts a thousand Ohms a thousand Farads a thousand Henry a thousand Hertz
Unit
 Base Unit
 A Volt
 An Amp A Watt
 An Ohm
 A Farad

10-3 milli
 a thousandth of a Volt a thousandth of an Amp a thousandth of a Watt a thousandth of an  Ohm a thousandth of a Farad
 a thousandth of a Henry a thousandth of a Hertz
10-6 micro
 a millionth of a Volt a millionth of an Amp a millionth of a Watt a millionth of an  Ohm a millionth of a Farad a millionth of Henry a millionth of Hertz
10-9 mano
 a billionth of a Volt a billionth of an Amp a billionth of a Watt a billionth of an  Ohm a billionth of a Farad a billionth of a Henry a billionth of a Hertz
10-12 pico
 a trillionth of a Volt a trillionth of an Amp
 a trillionth of a Watt a trillionth of an  Ohm a trillionth of a Farad a trillionth of a Henry a trillionth of a Hertz