009-Resistance-and-resistivity Physics Science Senior High

Physics

1. ELECTRICAL RESISTANCE

2. ELECTRICAL RESISTANCE

3. Resistance
•the measure of
the opposition
to current flow
in an electrical
circuit.

4. RESISTORS

5. RESISTOR
•It isa passive
two-terminal
electrical
component that
implements
electrical
resistance as a
circuit element.

6. RESISTOR
•In electronic circuits,
resistors are used to reduce
current flow, adjust signal
levels, to divide voltages, bias
active elements, and terminate
transmission lines, among
other uses.

7. SETS OF SYMBOLS USED TO
REPRESENT RESISTORS

8. COLOR
CODES for
RESISTORS

9. COLOR CODES
for RESISTORS
•The resistance
of the resistor
is indicated at
its exterior or
given in the
form of a color
code.

11. Example:
1. What is the
resistance
coefficient of a
resistor if its color
code is red – violet
– yellow – black –
gold?

12. Example:
2. What color
code
corresponds to
a resistance of
234 x 10
5
+10%?

13. Solve for the resistance of the given
resistors:
1
st
band 2
nd
band 3
rd
band 4
th
band
Resistance
value
Brown RedBrown Gold
Orange BlackBlackGold
YellowGreen Red Silver

14. FACTORS
AFFECTING
THE
RESISTANCE
OF A
UNIFORM
WIRE
1.Cross – sectional
area
2.Length
3.Material of a wire
4.Temperature

15. 1. CROSS –
SECTIONAL AREA
•Resistance R
varies
inversely
from the
cross –
sectional
area A of
the wire.

16. 1. CROSS –
SECTIONAL AREA
•Equivalently,
R
1A
1 = R
2A
2
Or
R
1
R
2
=
A
2
A
1

17. 2. LENGTH
•The resistance of a wire is
directly proportional to its
length.
•A longer wire has greater
resistance than the
shorter wire of the same
material and cross –
sectional area.
R
1
L
1
=
R
2
L
2

18. 3. MATERIAL
OF A WIRE
•The effect of the kind
of material on the
resistance of the wire
is determined by its
resistivity.
•Resistivity (ρ) is the
reciprocal of
conductivity.

19. The effect of length, cross – sectional area
and material on resistance may be written as

20. Resistivity
values for
various
materials at
temperatures of
20 degrees
Celsius.

21. Example:
1.Compute the resistance of a
conductor given a resistivity
of 10.4 Ω.m, length of 4 m
and cross – sectional area of
7.85x10
3
m
2
.

22. 4. TEMPERATURE
•Resistance and resistivity
vary with temperature.
•As temperature
increases, resistance and
resistivity increase for
conductors and decrease
for insulators and
semiconductors.