Download Name: Addie Laurente Title: Resistivity Purpose: To use Ohm`s Law

Name: Addie Laurente
Title: Resistivity
Purpose: To use Ohm’s Law and the math model for resistance to Predict & Test the resistivity
of #30 gauge nickel silver.
Apparatus: Circuit (Power Supply, Ammeter, and Voltmeter), 4 resistors (0.80, 1.20, 1.60, 2.00)
(m).
(m).
Sample Calculations:
 R (Ohms) : V= IR
o 2 = 0.04 R
o R = 5Ω
 ρ = R( π r2) / L
o ρ = 5 ( π) (0.000127)2 / 0.80
o Ω Ω = 3.17 x 10-7 Ω•m
Data & Calculations:
L (m)
V (Volts)
I (Amps)
0.80
1.20
1.60
2.00
2
2
2
2
0.4
0.26
0.2
0.15
R (Ohms)
ρ (Ω•m)
5
3.17 x 10-7
7.69
3.25 x 10-7
10
3.17 x 10-7
13,33
3.38 x 10-7
Theoretical: 3.3 x 10 -7
Questions:
1. a) If R80cm = 4.4 Ω, then R40cm = 2.2Ω
b) V = IR
2V = I (.4)
I = 5 Amps
The predicted current through the 40 cm resistor for a voltage of 2V was predicted to
be about 5 amps. The prediction is tested by using the circuit set up and a 40 cm resistor,
and the prediction was fairly accurate because the tested current value was about 4.97
Amps.
2. Resistance can be found by using the equation V = IR. The V and I values can be found
by using the ammeter and the voltmeter. The gauge and ruler can also be used to find the
resistance value.
Summary:
A circuit is set up just as it is portrayed in a diagram with a power supply, voltmeter, and
ammeter. Four resistors of different lengths, 0.80, 1.20, 1.60, and 2.00 m, are connected to the
power supply and two meters. For each resistor the power supply is adjusted so there is 2 Volts,
and the corresponding I (Amps) value is recorded. The I values are 0.4, 0.26, 0.2, and 0.15 Amps,
respectfully. With the found values of V and I, the resistance (R) can be calculated by using the
equation V = I R. After plugging the data into the equation, the calculated R values are 5, 7.69,
10, and 13.33Ω, respectfully. After finding the R value, the resistivity (ρ) can be found by using
the equation ρ = R(π r2) / L. The given radius (r) value is 0.000127 m. After plugging in the
needed data into the equation, the calculated ρ values are 3.17 x 10-7, 3.25 x 10-7, 3.17 x 10-7, and
3.38 x 10-7 Ω•m, respectfully. These predicted values are tested by being compared to the
theoretical value of resistivity, 3.3 x 10-7. The predicted values are reasonable because they have
the same order of magnitude as the theoretical value, meaning that the values are very similar.
Error Sources:
1. The resistors may have not been measured accurately, affecting the L value of the data.
2. The voltmeter may have not completely stopped at 2V, affecting the I value and the
calculated R and ρ values.
3. The ammeter may have not been read accurately, affecting the calculated R and ρ values.