Table of Contents

Abstract Page 3

Procedures and Results Page 4

Discussion and Conclusion Page 11

References Page 13

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ABSTRACT

As a first experiment in the electric circuits and devices course, this experiment had the purpose

of mainly helping us become familiar with the basic equipment used in the lab, such as the

circuit boards, resistors and how to read their resistance, connecting wires and the digital multi-

meters. The important knowledge required for this experiment would be that of Kirchoff’s

voltage and current laws for closed loop circuits, that of reading the color codes on resistors and

the ability to form a circuit while simultaneously adjusting it repeatedly to fit in voltmeters and

ammeters to get the readings when necessary.

The experiment was divided into four basic parts:

Interpretation of color-coded resistors and measuring their real values using the digital

multi-meter. In this part, the resistances of four resistors were to be determined and

compared with their nominal values.

Verification of Ohm’s Law – Using Current and Voltage readings to do calculations and

analysis in order to come to the conclusion that V=IR.

Kirchoff’s Voltage and Current laws: Using the four resistors connected in a circuit,

Kirchoff’s laws were to be verified using the Voltage and Current values measured at

several points in the circuit.

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Procedure and Results:

Part I: Measuring resistor values by color code.

The first part of the experiment included determining the nominal values of four different

resistors using the color code table shown below.

Figure 1: Resistor Color Code Chart

The first two bands give the first two digits respectively of the nominal value of the resistance

and the third band is the multiplier by which the first two digits combined are multiplied. The

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fourth band gives the tolerance level of the resistor. For instance, if the color code is Blue, Black,

Brown, Golden, then the nominal value is calculated as:

R=60× 101 ±5 % Equation (1)

The resistance values of all four resistors were then measured using the digital multi-meter.

Finally, the percentage error was calculated using the following equation:

PE (Percentage Error )=Measured−NominalNomial

∗100 % Equation (2)

The data collected is shown below:

Resistor R1 R2 R3 R4

Nominal Value (Ω) 470 820 2200 680

%Tolerance 5% 5% 5% 5%

Measured Value

(Ω)

485 808 2161 678

PE (%) 3.19 1.46 1.77 0.29

Table 1: Resistance measurements

Part II: Voltage and Current Measurements to verify Ohm’s law

In the second part of the experiment, the relationship between voltage and current was analysed

by passing current through an unknown resistor was connected in series with an ammeter and a

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variable DC power supply as shown in the figure below. The DC power supply was varied

between 1V and 10V with increments of 1V and each time, the current passing through the

resistor was measured using the voltmeter and the ammeter. The current values were recorded in

a table and the resistance for each increment in voltage was calculated and recorded in the table

using Ohm’s Law(R = V/I) and its average came out to be 0.675kΩ which is similar to its

measured value of 678 Ω.

Figure 2: Circuit Diagram (Part B)

The graph of V versus I was plotted from the collected data and the slope was measured to

calculate the resistance value.

Reading

No.

Voltage

(V)

Current

(mA)

Resistance

(V/I, Ω)

1 1 1.47 0.68

2 2 2.94 0.68

3 3 4.43 0.68

4 4 5.99 0.68

5 5 7.41 0.67

6 6 8.97 0.67

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7 7 10.35 0.67

8 8 11.81 0.67

9 9 13.45 0.67

10 10 14.82 0.67

Table 2: Voltage and current measurement (Part B)

Part 3: Kirchoff’s Voltage and Current Laws

In this part, the four resistors are connected as shown below:

Figure 3: Circuit for Kirchoff’s Voltage and Current laws (Part C)

Here, the Kirchoff’s laws (KVL and KCL) need to be verified. The following data need to

measured:

Voltages:, V10, V20, V30, V12, V23

Currents: I12 , I23 , I20

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After this we substitute the values into the following equation in order to verify both KVL and

KCL:

V 23+V 30+V 02=0 Equation (3)

−I 12+ I 23+ I 20=0 Equation (4)

Part 3: Data collected

Voltage

(V)

V10 V20 V30 V12 V23

DMM 15.1 -8.02 2.157 6.98 5.51

Table 3: Node voltages (Part C)

Current

(A)

I12 I23 I20

DMM 14.46 11.90 2.56

Measuring the voltages around the path 2-3-0, KVL is confirmed as follows:

V 23+V 30+V 02=0

5.51+2.517−8.02=0.007

Hence, KVL is also confirmed. The small differences in values are due to experimental errors,

which are further discussed in the discussion.

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Similarly, KCL for node 2 is confirmed as follows:

−I 12+ I 23+ I 20=0

−14.46+11.90+2.56=0

Hence, KCL is verified and the law is in complete agreement with the experiment.

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DISCUSSIONS AND CONCLUSIONS

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In this experiment we had to verify Ohm’s law and Kirchhoff’s laws. We started off by

measuring the resistance of the multimeter by reading off the digital multimeter. The second

section consisted of the resistor and checking the actual resistor value from the coloured stripes

present on it. In this method, the first and the second colour band represents the digit from the

table. The third band represents the multiplier and finally, the last colour represents tolerance.

After the both the evaluations were finished we noticed that the percent difference (3.19, 1.46,

1.77 & 0.29) was always lower than the tolerance value (5%).

In the second experiment, we let current flow through a resistor and the voltage was varied from

the power supply by increments of one volt from 1-10V. By this method we verified Ohm’s Law

as we as the relation between current and the voltage was linear.

Then we had to verify both of Kirchhoff’s Voltage and Current laws. As displayed by the values

above the sum of the voltage drops were found to be 0.007, which is not exactly equal to zero.

This may be due to human errors and errors in measurements and instruments; also keeping in

mind the fact that difference is very minor and can be negligible The Current Law showed that

the sum of the currents entering and exiting the node.

The main sources of errors in this experiment were the presence of human errors, errors in

measurement and instrument errors.

In conclusion it can be said that all the experiments were done fairly accurately with satisfactory

results. Although the digital multi-meter gives us a better and more accurate reading of the

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resistance the colour coding is more suitable when many resistors have to be sorted through.

KVL and KCL were also confirmed to be true inside a closed loop.

REFERENCES

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Ohm’s Law and Kirchoff’s Law Verification. Lab script. Spring 2014

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