5 109
Ω m.
.
m m
m
Example 2
Calculate the resistance 100m aluminium cable 1.
.4 10–9
Ω which means that
a sample silver long and cross-section will have resistance
of 16. Therefore, aluminium cable is
to replace copper cable, the conductor size must increased carry the rated current as
given the tables Appendix the IEE Regulations and Appendix the Site Guide.
The other factor which affects the resistance material the temperature, and will
consider this later.
Example 1
Calculate the resistance 100m copper cable 1.
R
l
a
ρ
( )
∴
28 100
1 10
1 9
9
6 2
.5mm2
cross-sectional area the
resistivity aluminium taken 28.4 10–9
Ω.
Basic mechanics and machines
Definition
Mechanics the scientific study of
‘machines’, where machine defined
as device which transmits motion or
force from one place another.
m m
m
The above examples show that the resistance aluminium cable some 60% greater than
a copper conductor the same length and cross-section.
.
Key Fact
Resistance the length doubled,
resistance will doubled.5 109
Ω m. the csa is
doubled, the resistance will halved.5mm2
cross-sectional area the
resistivity copper taken 17.
.
Ω
Ω
Mechanics the scientific study ‘machines’, where machine defined
as device which transmits motion force from one place another.3 gives the resistivity silver 16.
Try This
Resistance
● Take two 100m lengths singles cable coils)
● Measure the resistance 100m cable coil)
Value ______________________________
● Join the two lengths together (200m) and again measure the resistance
Value ______________________________
Does this experiment prove resistance proportional length?
If the resistance doubled, proved! QED, Quo Erat Demonstration (Latin
for proved).Basic Electrical Installation Work
84
Table 4.
.
R
l
a
ρ
( )
∴
17 100
1 10
1 16
9
6 2
. An
engine one particular type machine, energy-transforming machine,
converting fuel energy into more directly useful form work
