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The very first steps
Electronic components
The fact that different resistances produce different currents
if a voltage is applied across them, or produce different voltages
if a current is applied through them, is one of the most
useful facts in electronics.
In electronics, an amp of current is very large — usually we
only use much smaller currents, say, a thousandth or so of
an amp. Sometimes we even use currents smaller than this,
say, a millionth of an amp! Similarly, we sometimes need only
small voltages, too.
Resistances are extremely useful in these cases, because
they can be used to reduce the current flow or the voltage
produced across them, due to the effects of Ohm’s law. We’ll
look at ways and means of doing this in the next chapter.
All we need to know for now is that resistances are used in
electronics to control current and voltage.
Table 1.1 shows how amps are related to the smaller values
of current. A thousandth of an amp is known as a milliamp
(unit: mA). A millionth of an amp is a microamp (unit: µA).
Current name Meaning Value Symbol
amp — 10 0 A A
milliamp one thousandth of an amp 10 -3 A mA
microamp one millionth of an amp 10 -6 A µA
nanoamp one thousand millionth of an amp 10 -9 A nA
picoamp one million millionth of an amp 10 -12 A pA
femtoamp one thousand million millionth of an amp 10 -15 A fA
Table 1.1
Comparing amps with smaller values of current
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