1445326735900-0

The very first steps
Larger values of voltage are the kilovolt, that is, one thousand
volts (unit: kV) and the megavolt, that is, one million volts
(unit: MV). In electronics, however, these are never used.
Resistors
The components which are used as resistances are called,
naturally enough, resistors. So that we can control current
and voltage in specified ways, resistors are available in a
number of values. Obviously, it would be impractical to have
resistors of every possible value (for example, 1 Ω , 2 Ω , 3 Ω,
4 Ω) because literally hundreds of thousands — if not millions
— of values would have to exist.
Instead, agreed ranges of values exist: and manufacturers
make their resistors to have those values, within a certain
tolerance. Table 1.3 (over) shows a typical range of resistor
values, for example. This range is the most common. You
can see from it that large values of resistors are available,
measured in kilohms, that is, thousands of ohms (unit: kΩ)
and even megohms, that is, millions of ohms (unit: MΩ). Sometimes
the unit Ω (or the letter R if used) is omitted, leaving
the units as just k or M.
Resistor tolerance is specified as a plus or minus percentage.
A 10 Ω ±10% resistor, say, may have an actual resistance
within the range 10 Ω –10% to 10 Ω +10%, that is, between
9 Ω and 11 Ω .
As well as being rated in value and tolerance, resistors are
also rated by the amount of power they can safely dissipate
19