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MINISTRY OF EDUCATION
SECRETARY OF MEDICAL AND TECHNOLOGICAL EDUCATION
FEDERAL INSTITUTE OF EDUCATION, SCIENCE AND TECHNOLOGY - AM.
GRADUATION TEACHING BOARD
ANA LÍVIA FERREIRA PONTES
JOSEH EMMANUEL DE SOUSA GOMES
LUCAS DA SILVA COSTA
PAULO HENRIQUE L COUTO
VICTOR HUGO TAVARES NEVES
PHYSICS III
MANAUS
2018
ANA LÍVIA FERREIRA PONTES
JOSEH EMMANUEL DE SOUSA GOMES
LUCAS DA SILVA COSTA
PAULO HENRIQUE L COUTO
VICTOR HUGO TAVARES NEVES
EXPERIMENTAL PRACTICE
OHM LAWS
Report presented as a partial requirement for approval in the
discipline PHYSICS III, of the course Mechanical
Engineering, taught by Prof.MsC J. Anglada Rivera.
MANAUS
2018
3
1.
INTRODUCTION
Electrodynamics aims to study situations where electrically charged particles,
electrons, lose their electrostatic equilibrium and begin to move in an ordered direction.Every
time there is a displacement of electrons towards a specific direction has called electrical
current.
In order for this movement to occur it is necessary to have a Potential Difference
(ddp) between two points known as electric voltage, it will be responsible for allowing the
locomotion of these electrons and thus flowing the current.As electrons move, they encounter
natural oppositions presented by matter that characterize electrical resistance.
The laboratory practice reported in this paper was directed to the analysis and
understanding of such phenomena of electrodynamics as expressed by the Ohm Laws.Being
divided in two practical parts, the first one has the purpose of the analysis of the First Law of
Ohm and the following of the Second Law of Ohm.
4
2.
EXPERIMENTAL PROCEDURES
2.1. PRIZE PRACTICE OF PHYSICS LABORATORY 3
Objective: To verify experimentally the law R = U / i
Materials: Ohm's Law Kit, Voltmeter, DC Power Supplies, Ammeter, Ruler and
Wiring Wires.
For the following experiment, we set up the circuit using the Ohm Law Kit,
selecting the Nickel-Chromium material to determine the intensity of the current, so that
through the formula R = U / i we obtain the value of the resistance
D(cm)
L (cm)
V(V)
I (A)
R (Ω)
0,072
20
3,3
0,30
11,0
0,072
40
5,0
0,45
11,1
0,072
0,072
60
80
6,6
8,3
0,60
0,75
11,0
11,067
We obtained the following plot of V = f (I), and through its angular coefficient R
= V1-V2 / (i1-i2) we obtain the same average value of the nickel-chromium wire resistance: R
= 11Ω.
5
Calculating the error in relation to the Nominal Value of the Resistance through
the resistivity of the nickel chromium material.We adopted the resistivity value 1.1x10 ^ -6 Ω
.cm, for this we used the formula for home measured value: E = (| R-Rn |) / RN) * 100
Error 1: 0.035%
Error 2: 0.018%
Error 3: 0.0011%
Error 4: 0.0012%
Choosing now another Resistance, the Iron, we obtained the following values:
D(cm)
L (cm)
V(V)
I (A)
R (Ω)
0,0051
20
2
0,30
6,67
0,0051
40
3
0,45
6,67
0,0051
60
80
4
0,60
6,67
5
0,75
6,67
0,0051
We obtained the following graph of V = f (I), and through its angular coefficient
R = V1-V2 / (i1-i2) we obtain the same average value of the resistance of the iron wire: R =
6Ω.
Calculating the error in relation to the Nominal Value of the Resistance through
the resistivity of the nickel chromium material.We adopted the resistivity value 1x10 ^ -7 Ω
.cm, for this we used the formula for home measured value: E = (| R-Rn |) / RN) * 100
Error 1: 0.01708%
Error 2: 0.00854%
Error 3: 0.00566%
Error 4: 0.00425%
6
By means of these experimental data it is possible to prove the relationship R = U
/ i, confronting with the nominal values and to perceive a very small error index,
corroborating the affirmation of the first Ohm Law.
2.2. SECOND PHYSICS LABORATORY PRACTICE 3
I - Dependence of R of length L
For the following experiment, the Ohm Law Kit was used, selecting the IRON
material to perform the variations of length L (m) according to the table below:
S(cm2)
V(V) I (A) L (cm) p (Ohm*cm) R(Ohm)
0,000000081
0,4
0,15
0,4
0,000000540
2,67
0,000000081
0,4
0,1
0,6
0,000000540
4
0,000000081
0,4
0,07
0,8
0,000000579
5,71
0,000000081
0,4
0,06
1
0,000000540
6,67
For the obtained diameter, shown in the table above and with the variation of the
length for the same material, we obtained the resistance values through the formula: R = V / i:
V(V)
I (A)
L (cm)
R(Ohm)
0,4
0,15
0,4
2,67
0,4
0,1
0,6
4
0,4
0,07
0,8
5,71
0,4
0,06
1
6,67
We obtained the values of resistivity through the formula: ρ = R * S / L
S(cm2)
L (cm) p (Ohm*cm) R(Ohm)
0,000000081
0,4
0,000000540
2,67
0,000000081
0,6
0,000000540
4
0,000000081
0,8
0,000000579
5,71
0,000000081
1
0,000000540
6,67
Calculating the error in relation to the Nominal Value of the Resistance through
the resistivity of the iron material.We used the resistivity value 0.5 ^ -6 Ω .cm, for this we
used the formula for home measured value: E = (| ρ - ρ n |) / ρ N) * 100
Error 1: 0.4%
Error 2: 0.592%
Error 3: 0.866%
Error 4: 0.894%
7
II - Dependence of R of cross section S
For the following experiment, the Ohm Law Kit was used, selecting the material
Nickel-Chrome to perform the variations of cross-sections S (cm2) according to the table
below:
I
L
p
D(cm) S(cm2) V(V) (A) (cm) (Ohm*m) Rn(Ohm)
R (Ohm)
0,036 0,00102 3,7 0,35 10
0,00108
13,4
10,57142857
0,051 0,00204 3,7 0,68 10
0,00111
6,7
5,441176471
0,072 0,00407 3,7 1,64 10
0,00092
3,36
2,256097561
For the circuit below, we applied the voltage V according to the table, and we
obtained the following current measurements for the cross section change:
S(cm2)
V(V)
I (A)
0,00102
3,7
0,35
0,00204
3,7
0,68
0,00407
3,7
1,64
With the current values obtained it was possible to calculate the resistivity values
ρ through the formula ρ = V * S / I * L, we obey the following values:
S(cm2)
(V)
0
,00102
,7
0
,00204
,7
0
,00407
,7
V
(A)
3
,35
3
,68
3
,64
I
(cm)
0
0
0
0
1
0
L
ρ (Ohm*m)
1
0,00
108
1
0,00
111
1
0,00
092
The resistivity values for the different cross sections of NickelCromo allowed us
to calculate the resistance values of each wire through the formula: R = ρ * L / S
8
(cm2)
,00102
,00204
,00407
S
(cm)
0
0
0
0
0
0
L
(Ohm*m)
1
,00108
1
,00111
1
,00092
ρ
R
(Ohm)
0
1
0,57142857
0
5,
441176471
0
2,
256097561
Once the values are plotted, the following graph shows the inversely proportional
relationship between R and S, in addition that it does not follow a linear pattern and that as
the section increases the resistance decreases and consequently increases the intensity of the
current by the conductor.This is due to a larger area of electron passage and a decrease in the
collision between free electrons.
9
3.
CONCLUSION
In
practical
terms,
it
is
not
yet
possible
to
same results obtained through the theory, and this will occur by a series of factors.
Among the main ones: due to lack of instrument calibration, human error and
constant
approximation
of
values.These
final
results
will
always
be
accuracy,
which
will
set
the
error
variation
for
more
or
paramenes
In the case of this experiment, after a series of steps, it is concluded that the
experimental accuracy is relatively good considering the low nominal error.
It was possible to verify the approximations of the formulas of the first and second
laws of Ohm from nominal to experimental.
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