Electronics 14

14.1 Introduction ESCGA

Electronics and electrical devices surround us indaily life. From the street lights and

water pumps to computers and digital phones, electronics have enabled the digital

revolution to occur. Allelectronics are built ona backbone of simple circuits, and so

an understanding of circuits is vital in understanding more complex devices.

This chapter will explain the basic physics principles of many of the components of

electronic devices. We will begin with an explanation of capacitors and inductors. We

see how these are usedin tuning a radio. Next,we look at active components such as

transistors and operational amplifiers. Lastly, thechapter will finish with an explanation

of digital electronics, including logic gates and counting circuits.

Before studying this chapter, you will want to remind yourself of:

• The meaning of voltage (V ), current (I) and resistance (R), as covered in Grade
  10, and Grade 11.


• Capacitors in electric circuits, as covered in Grade 11 (see section 17.6).


• Semiconductors, as covered in Grade 11 (see chapter 20).


• The meaning of an alternating current (see section 28.3).


• Capacitance (C) and Inductance (L) (see section 28.4).

See introductory video:VPpml at http://www.everythingscience.co.za

14.2 Capacitive and Inductive Circuits

ESCGB

Earlier in Grade 12, you were shown alternating currents (AC) and yousaw that the

voltage and the currentvaried with time. If theAC supply is connectedto a resistor,

then the current and voltage will be proportional to each other. This means that the

current and voltage will‘peak’ at the same time. We say that the current and voltage

are in phase. This is shown in Figure14.1.

When a capacitor is connected to an alternatingvoltage, the maximum voltage is pro-

portional to the maximum current, but the maximum voltage does not occur at the