Page 278 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

3
262 Automobile mechanical and electrical systems

When voltage causes current to fl ow, energy is converted. This is described as
power. The unit of power is the watt. As with Ohm’s law, any one value can be
calculated if the other two are known.

Power Voltage Current
(P VI ) or (I P V/ ) or (V P/ ) I

Check the book website for the Ohm’s
law and power ‘magic’ triangles Electrical units are summarized in Table 3.1 .
All metals are conductors. Silver, copper and aluminium are among the best
and are frequently used. Liquids that will conduct an electric current are called
electrolytes. Insulators are generally non-metallic and include rubber, porcelain,
glass, plastic, cotton, silk, wax, paper and some liquids. Some materials can act
as either insulators or conductors depending on conditions. These are called
semiconductors. They are used to make transistors and diodes ( Fig. 3.8 ).

Table 3.1 Electrical units summary
Name Defi nition Name Symbol Abbreviation

Electrical fl ow The number of electrons Ampere I A
or current past a fi xed point in one
second
Electrical A pressure of 1 volt Volt V V
pressure applied to a circuit will
produce a current fl ow
of 1 amp if the circuit
resistance is 1 ohm
Electrical The opposition to Ohm R Ω
resistance current fl ow in a material
or circuit when a voltage
is applied across it

Electrical When a voltage of Watt P W
power 1 volt causes a current
of 1 amp to fl ow the
power developed is
1 watt

Figure 3.8 Semiconductor transistors