This document discusses how various factors affect the resistance of electrical conductors. It states that resistance depends on the length, cross-sectional area, material, and temperature of the conductor. Longer wires, thinner wires, and materials with higher resistivity all result in higher resistance. Additionally, increasing the temperature of a conductor causes its resistance to rise as well. Various materials and their resistivities are listed to illustrate differences. Resistance is directly proportional to length and resistivity, and inversely proportional to cross-sectional area.

1. Length, Cross-Sectional Area,
Kind of Material, Resistivity and
Temperature: The ir Re latio nships
FACTORS AFFECTINGFACTORS AFFECTING
RESISTANCERESISTANCE

2. Conductors will always allow the
flow of current.
Electrical cords or wires are the
best and common examples of
conductors used in our house.
Are all electrical wires used in our
house of same size, length, and
kind of material?
FACTORS AFFECTING
RESISTANCE…

3. RESISTANCE OF A
MATERIAL…Resistance of the conducting wires
used in electric circuits varies with
the dimension of the length and area,
and depends on the material the wire
is made of.
Using different lengths of wire will
affect resistance. It can be
illustrated by the following…
CaseCase

4. LENGTH OF THE WIRE …
In the previous illustration, it is
noticeably visible that the case 1-
bulb is brighter than the case 2-bulb.
This can be summarized as “the
lo ng e r the co nducting wire , the hig he r is its
re sistance ”. This means that
resistance is always affected by the
length of wire; or L α R.
In a particle approach, it can be

5. LENGTH OF MATERIAL …
Variable resistors (wire-wound) are
best examples of conductors made
of a long wire looped around
insulator bases, used to regulate
current. The volume control of a
radio is a variable resistor.
“As the volume knob is turned, the
effective length of the resistance

6. RESISTANCE AND WIRE’s
DIAMETER …How does a wire’s diameter affect
its resistance?
Consider this illustrations…
The illustration simply shows that
“the big g e r & thicke r the wire , the le sse r is
++ + +-
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- -
-
-
-
-
- --
-
-
+
+
+
+
- -
-
-
- -
-
- - - -
-
-
-
- -
-- -
-
A wire with
smaller
diameter.A wire with
larger
diameter.

7. WIRE’s DIAMETER …
It is very important that the loads in a
circuit be limited to the amount of
current that the wire can safely carry;
WIRE GAUGEWIRE GAUGE WIRE’s CURRENT CARRYING CAPACITYWIRE’s CURRENT CARRYING CAPACITY
1414 15 A15 A
1212 20 A20 A
1010 30 A30 A
*WIRE GAUGE &*WIRE GAUGE &
CORRESPONDING CURRENTCORRESPONDING CURRENT
RATING.RATING.

8. RESISTANCE IN DIFFERENT KIND
OF MATERIALS …Resistance of an ohmic conductor
also depends on the kind of
material it is made of. The
composition of materials greatly
affect their ability to conduct. This
means that electric current varies
more than almost any other
physical property of a material.

9. RESISTANCE OF DIFFERENT
MATERIALS …Resistivities (at 20o
C) of
different materials.MATERIALSMATERIALS RESISTIVITY (RESISTIVITY (ΩΩ.m).m)
SilverSilver 1.59 x 101.59 x 10-8-8
CopperCopper 1.70 x 101.70 x 10-8-8
GoldGold 2.44 x 102.44 x 10-8-8
AluminumAluminum 2.82 x 102.82 x 10-8-8
TungstenTungsten 5.60 x 105.60 x 10-8-8
IronIron 1.00 x 101.00 x 10-7-7
Stainless SteelStainless Steel 7.20 x 107.20 x 10-7-7
PlatinumPlatinum 1.10 x 101.10 x 10-7-7

10. Continuation of Materials’ Resistivity
… Resistivities (at 20o
C) of
different materials.MATERIALSMATERIALS RESISTIVITY (RESISTIVITY (ΩΩ.m).m)
LeadLead 2.20 x 102.20 x 10-7-7
NichromeNichrome 1.50 x 101.50 x 10-7-7
CarbonCarbon 3.50 x 103.50 x 10-5-5
GermaniumGermanium 4.60 x 104.60 x 10-1-1
SiliconSilicon 6.40 x 106.40 x 10+2+2
GlassGlass 10101010
–– 10101414
Hard RubberHard Rubber approx. 10approx. 101616
SulfurSulfur 10101515

11. MATERIAL’s RESISTIVITY …
Re sistivity (ρ) is the reciprocal of
co nductivity. The list of resistivities of
materials clearly show that
resistance varies depending on the
what kind of material a conductor is
made of.
The temperature of a wire also
affects the resistance of the wire. For

12. TEMPERATURE AFFECTING
RESISTANCE …As the temperature increases, the
atoms in the wire vibrate more
vigorously. The conduction of
electrons would make more
collisions with the vibrating atoms.
The resistance of the wire would
increase. In the event that the wire
is hot, it will have a greater
resistance than a cool wire.
R
A

 L

13. LENGTH OF MATERIAL …
where:
ρ= resistivity of the conductor in
Ω.m.
L = length of the conducting wire
used.
A = cross-sectional area of the
conductor (m2
)
R
A

 L