Miniaturisation did not stop with the invention of the transistor. Photographic processes are used to form millions of connected semiconductor components on thin wafers of treated silicon, sometimes called silicon chips. The finished product is called an integrated circuit (IC) or microchip. Microchips are now used in most electrical products, such as burglar alarms, car indicators and computers. Scientists are continually finding ways to pack more components onto a single chip—in fact, the number has roughly doubled each year since 1965.
Diodes may be used to protect circuits from current going the ‘wrong way’ and damaging sections of the circuit, and for converting AC to DC. A special kind of diode is the light-emitting diode (LED), which is used in indicator lights and digital displays.
Transistors
The transistor is the most famous electronic component of all and was invented in 1947 by a team from Bell telephone laboratories led by William Shockley. Like the diode, it is made from treated silicon, and is a type of semiconductor. The transistor, however, contains three layers of treated silicon.
Transistors come in many shapes and sizes. Fig 3.5.11
C B E
emitter current
basic current
Fig 3.5.12 Note the position
of each leg in this diagram of a transistor.
LED the light shine
LEDs are far more energy efficient than light bulbs, but you need a lot of them to produce the same light. Traffic lights are gradually being changed from single
bulbs to banks of LEDs. The main advantage here is
that LEDs don’t all ‘blow’ at once … there are always some left to keep the traffic light operating until its next
regular servicing.
Modern printed circuit boards connect integrated circuits and separate components
together in a compact way. Fig 3.5.13 integrated circuit
resistor
integrated circuits
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3.5
UNIT
[
Questions
]
Checkpoint
Resistors1 Outline the function of a resistor in a circuit.
2 Identify the feature that distinguishes different-sized
resistors.
Thermistors
3 Define the term ‘thermistor’.
4 State three potential uses for a thermistor.
Light-dependent resistors
5 Modify the following statements to make them correct. a An LDR has a constant resistance.
b More light increases the resistance of an LDR c An LDR cannot be used in changing light conditions.
Capacitors
6 Outline the purpose of a capacitor.
7 A dielectric assists in storing the charge in a capacitor.
Use a diagram to demonstrate how this works.
8 Identify the units used to describe capacitance.
Diodes
9 State two uses for a diode.
10 Two elements are often used to make semiconductors. State their names.
11 A diode is considered a one-way valve for current. Outline how this is achieved.
Transistors
12 State the name of the members of the team that
developed the first transistor.
13 Construct a diagram explaining how to identify the
base, collector and emitter legs of a transistor.
14 Transistors were a major advance in electronics. Explain
why.
Integrated circuits
15 A microchip is also called an integrated circuit or a
silicon chip. Explain how these terms are connected.
16 Microchips are a major breakthrough in electronics. List two uses of microchips.
Think
17 Identify the type of component described in this unit
that may be a key part of:
a the control of an air conditioner b automatic doors
18 Many bicycle lights involve one or more flashing LEDs. Outline the advantages of having the LEDs flash. 19 a Evaluate whether ENIAC would fit in your bedroom.
b If not, calculate how many rooms of that size would
be needed.
20 Estimate how many components may be fitted on a
silicon chip next year compared to this year.
Analyse
21 Calculate the resistance of each
of the following resistors:
a blue, grey, brown b brown, green, orange c red, violet, yellow d red, green, green 22 For each of the following
resistors identify the colours (in order) of the first three bands:
a 560 Ω b 3300 Ω c 470 000 Ω d 1 200 000 Ω
Electronics
Electronics
Fig 3.5.15 Fig 3.5.14ENIAC—Electronic Numerical Integrator and Calculator—was the first electronic computer.
Prac 6 p. CD22 Prac 5 p. CD22 Prac 4 p. CD21 ENIAC
The first fully electronic digital computer, called ENIAC, was completed in 1947—the same year
that transistors were invented. It took up 170 square metres of
floor space—compare this to today’s computers, which can fit
UNIT
UNIT
3.5
3.5
Component Sketch Use Symbol
Resistor
Detects light
Transistor
Skills
23 Complete the table opposite, identifying words
from the text for the missing names of electronic components.
24 Use several small rectangular light-emitting diodes
to demonstrate how the digits 0 to 9 on a digital clock display may be constructed.
25 Construct a circuit diagram for the circuit shown
here.
26 Calculate how many times smaller a transistor is
than an old-style valve. 9 V + – 330 μF Fig 3.5.16
[Extension]
Investigate
1 3K8 is another way of labelling a 3800 Ω
resistor.
a Explain what 4K9 means. b Explain what 2M5 means.
2 a Clarify what is meant by ‘p’ and ‘n’
type germanium.
b Describe how it is used to make diodes. 3 a Explain how diodes can be used to convert
alternating current to direct current.
b State the name given to such a circuit. 4 a Describe what is meant by ‘logic gates’.
b Use diagrams to demonstrate different types
of logic gates.
5 Describe what is meant by a ‘microprocessor’.
6 Justify the use of the term ‘Silicon Valley’. 7 Explain what is meant by ‘CSIRAC’.
Surf
8 Complete the tutorials on resistors and
resistor colour codes and record the results in a table showing the coloured bands on the resistors and the resistance
they correspond to. You will find a link by connecting to the Science Focus 4 Companion Website at
www.pearsoned.com.au/schools, selecting chapter 3
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Prac 2 Unit 3.5