Name :
Date of Report :24th Feb 2018
Course : PHY 134
TA : Jose Miguel Bautista, Sahand Seifnashri, Yanzhu Chen, John Tucker, Hui Li, Norton Lee
Ohm’s Law
Introduction:
The goal of this experiment is to measure the current and voltage of six different types of
circuits and to compare the theoretical value of current with the actual current flow using Ohm's
law. Ohm’s Law is given by the formula V=I*R, where I is the current floating in a circuit loop,
V is the voltage, and R is the resistance of the resistor. The IOLab device is used as the power
supply, and the input voltage is 3.3v. This experiment consists of four series connection circuits,
one parallel connection circuits, and one combination circuit. The equivalent resistance when the
resistors in a circuit are connected in series and in parallel are Req = R1 + R2 + ⋯ +
1
1
1
1
1
Rn and 𝑅𝑒𝑞 = 𝑅1 + 𝑅2 + 𝑅3 + ⋯ + 𝑅𝑛 , respectively. These equations are derived from kirchoff's
law. The input vlotage in this lab is constant at 3.3v, so we can expect that the value of the
current will change as the resistance value changes. According to Ohm's law, resistance and
current are inversely related to each other. Therefore, Req and actual current flow will be
inversely related to each other.
Procedure:
1. Connect 3.3v pin of the device to + power rail and connect GND pin to – power rail.
2. To measure the input voltage, make a circuit of two 10k ohms connected in series.
3. Connect the analog input pin of the IOLab device to the second 10k ohm resistor in parallel.
4. For the first circuit, connect a 10k ohm resistor and a 1 ohm resistor in series and measure the
current through 1 ohm.
5. Replace the 10k ohm resistor of the 1st circuit with a 4.7k ohm resistor and measure the
current flow on the 1 ohm resistor.
6. For the third circuit, connect two 10k ohm resistors to an one ohm resistor in series and
measure the current flow on the 1 ohm resistor.
7. Replace the 10k ohm resistor of the 1st circuit with a 4.7k ohm resistor and measure the
current flow on the 1 ohm resistor.
8. For the fifth circuit, connect two 10k ohm resistors to + rail in parallel and connect the two
resistors to 1 ohm resistor in series, and then take measurement of the current flow on 1 ohm
resistor.
9. For last circuit, connect two 10k ohm resistors to + rail in parallel and connect one 4.7k ohm
resistor to one of the 10k ohm in series. Connect a 4.7k resistor to 4.7k and 10k ohm in parallel.
Results:
Figure 1 Input voltage
Figure 2 Current for the first circuit
Figure 3 Current flow for circuit 2
Figure 4 Current flow for circuit 3
Figure 5 Current flow for circuit 4
Figure 6 Current flow for circuit 5
Figure 7 Current flows on circuit 6
Calculation:
The input voltage is 1.65v × 2 = 3.3v.
1st circuit
2nd circuit
3rd circuit
4th circuit
5th circuit
6th circuit at top node
6th circuit at bottom node
6th circuit at middle node
Theoretocal Req (ohm)
10k
4.7k
10k + 10k = 20k
4.7k + 4.7k = 9.4k
(1/10k+1/10k)^-1 = 5k
Theoretical I (mA) Actual I(mA)
3.3 / 10k = 0.33
3.3/4.7k = 0.70
3.3/20k = 0.17
3.3/9.4k = 0.35
3.3/5k = 0.66
i1-i2 = 0.16
i2 = 0.22
i1 = 0.37
Figure 8 Results
The theoretical values of current in 6th circuit were obtained by current-mesh analysis.
% Diff.
0.38
0.72
0.22
0.39
0.69
0.13
0.18
0.34
15%
2.80%
30%
11%
4.50%
19%
18%
8%
Figure 9 Current-Mesh analysis for circuit 6
Discussion and conclusion:
In this experiment, the current was inversely proportional to the resistance when the
voltage was constant. It was also found that the voltage across each resistor is half of the input
voltage when two resistors of the same value are connected in series. It has also been found that
when a voltage is constant, almost all of the current flows to a low-resistance resistor when a
resistor having a relatively high resistance value and a resistor having a relatively low resistance
value are connected in series. Experimental results show that the percentage difference is not that
low. Given that the tolerances of the resistors are less than 3 percent, the errors in the
experimental results seem to be inaccurate for the IOLab device.