1. Factors Affecting
Resistance
Reported By: Ralph Lery Guerrero
Kevin Roxas
Marco Lauro Delos Santos

2. Resistance
• Is defined as an obstacle to
the flow of electric current.
• Is the opposition offered by
any object to the passage of
an electric current through
it.

3. Length
• Resistance of a conductor is directly
proportional to the length of the wire i.e.,
longer the wire greater will be the
resistance and shorter the wire smaller will
be the resistance. If L represents the length
of the uniform wire, then
RL

4. Length
R1/R2=l1/l2
Where
R1= resistance of the first conductor(in ohms)
R2= resistance of the second conductor(in
ohms)
l1=length of the first conductor (in cm)
l2=length of the second conductor (in cm)

5. Length
• Resistivity- is the resistance per unit
length of a specific substance to
electric force.

6. Length
• The volume control of your radio is a
variable resistor. As you turn the
volume control knob, the effective the
length of the resistance changes.
• Resistance and the amount of current
passing through the circuit change,
making the sound from the speaker
soft and loud.

7. Diameter (Cross-sectional area)
• Resistance of a conductor is inversely
proportional to the area of the cross-
section of the uniform wire. That means,
thinner the wire, greater the resistance
and thicker the wire, lower the
resistance. If A is the area of cross-
section of the uniform wire, then,

8. Diameter (Cross-sectional area)
If the cross-sectional area is
doubled, twice as many electrons
became available to flow so that
the current is doubled.

9. Diameter (Cross-sectional area)
R1/R2=d22/d12
Some connecting wires are made of stranded thin
wires.
Stranding wires has the same effect as increasing
cross-sectional area.
The wire’s gauge number specifies its size. The
smaller gauge number, the thicker the wire.
Hence, the lesser the resistance of the
conductor.

10. Diameter (Cross-sectional area)
Problem
An iron wire conductor with a
diameter of 0.8 mm has a
resistance of 0.4 ohm Ω. Calculate
the resistance of a n iron wire 0.4
mm in diameter.
Find:
R2

11. Diameter (Cross-sectional area)
Given:
R1=0.4Ω
d1=0.8mm
d2=0.4mm
Solution:
R1/R2=d22/d12
0.4Ω/R2=(0.4mm)2/(0.8mm)2
R2=(0.4Ω)(0.64mm)2/0.16mm2
R2=1.60Ω

12. Temperature
• The resistance of a metallic
conductor increases as the
temperature increases e.g.
copper
• The resistance of a
semiconductor/insulator
decreases as the temperature
increases

13. Temperature
Resistance increases with the temperature.

14. Kind of Material (Resistivity)
• The material also affects the
resistance of a conductor by a fixed
amount for different materials. This
is known as resistivity ().
R = L  = constant of proportionality
A

15. Kind of Material (Resistivity)
Resistors- conductors whose
resistance is constant when
the temperature is constant.

16. Kind of Material (Resistivity)
Material Resistivity (W m)
Conductors Silver 1.60 x 10-8
Copper 1.62 x 10-8
Aluminium 2.63 x 10-8
Tungsten 5.20 x 10-8
Nickel 6.84 x 10-8
Iron 10.0 x 10-8
Chromium 12.9 x 10-8
Mercury 94.0 x 10-8
Manganese 1.84 x 10-6
Constantan (alloy of Cu
Alloys 49 x 10-6
and Ni)
Manganin (alloy of Cu, Mn
44 x 10-6
and Ni)
Nichrome (alloy of Ni, Cr,
100 x 10-6
Mn and Fe)
Insulators Glass 1010 - 1014
Hard rubber 1013 - 1016
Ebonite 1015 - 1017
Diamond 1012 - 1013
Paper (dry) 1012

17. Kind of Material (Resistivity)
Problem
Given: Find:
L=15 m R
Diameter=0.085 cm
= 1.6x10-8 Ωm
T=20°C
Solutions:
Conversion: d= 0.085cm/100 cm x
1m
d= (8.5x10-4m)

18. Kind of Material (Resistivity)
a.) r=1/2d
r=8.5x10-4 m/2
r= 4.25x10-4 m
b.) A=πr2
A=(3.14)(4.25x10-4 m)2
A=5.67x10-7

19. Kind of Material (Resistivity)
c.) R = L
A
R=(1.6x10-8Ωm)(15m)
5.67x10-7m2
R=0.4Ω

20. Signing Off … By: RLUG
THANK YOU! =))