5 109
Ω m.
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.
R
l
a
ρ
( )
∴
17 100
1 10
1 16
9
6 2
. the csa is
doubled, the resistance will halved.
Ω
Ω
Mechanics the scientific study ‘machines’, where machine defined
as device which transmits motion force from one place another.5 109
Ω m.
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).4 10–9
Ω.
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.
. 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.
.
Example 1
Calculate the resistance 100m copper cable 1.3 gives the resistivity silver 16.Basic Electrical Installation Work
84
Table 4.
Key Fact
Resistance the length doubled,
resistance will doubled.
R
l
a
ρ
( )
∴
28 100
1 10
1 9
9
6 2
.
.
.5mm2
cross-sectional area the
resistivity aluminium taken 28.
m m
m
Example 2
Calculate the resistance 100m aluminium cable 1. An
engine one particular type machine, energy-transforming machine,
converting fuel energy into more directly useful form work.5mm2
cross-sectional area the
resistivity copper taken 17.
.4 10–9
Ω which means that
a sample silver long and cross-section will have resistance
of 16.
The other factor which affects the resistance material the temperature, and will
consider this later
