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Last updated: March 14, 2019

Experiment #3 Ohm’s Law and Resistance

By: Aisha Ali Sulaiman Mohamed Alnaqbi – H00367954

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Date: 18/10/2018
INTRODUTION:-

Objective:
1-This experiment will verify the relationship between the voltage(V) , resistance(R) and current(I) in a circuit to prove the Ohm’s Law.
2-Find the total resistance for series and parallel connection circuit

Theory:
Ohm’s Law deals with the relationships between the voltage(V) , resistance(R) and current(I). The relationships states that the voltage across a conductor between to point’s is directly proportional to the current. The constant of proportionality is called “resistance”. Ohm’s law expression: V=I R

We have two types for connecting the resistance:-

connecting the resistor in series and this the formula
R = R1 + R2 + R3…..Rn

connecting the resistor in parallel and this the formula
R=

To measure the currents the ammeters are connected in series.
To measure the voltages the Voltmeters are connected in parallel.

Material and equipment:

1- Varied values of resistors
2- Power supply
3- Power supply cables
4- Connecting wires
5- Multimeter
7- Jumper wires

Experimental set up and Procedure:

1- Measure using Multimeter the resistance of the three resistors listed in the table below Table.1 .
2- Use breadboard to connect R1 = 1.0 k into the circuit as shown in Fig.2
3- Adjust the power supply voltage at 2.0 V. Measure and record the current in Table.2 below: – Vary the voltage value as per the table below and record corresponding current reading for each of the voltages listed in the table below.
4- Draw I-V curve using the data from the above table Table.2. Plot the current on the y-axis and the
voltage in the x-axis. Find the slope of the straight line and compare with the value of R1 .
Comment on the graph.

5- Replace R1 with R2 ; R3 connected in series and repeat steps 3. Record the data in Table.3

6- Draw I-V curve using the data from the above table Table.3. Plot the current on the y-axis and the voltage in the x-axis. Find the slope of the straight line and compare it with the value of RT ( RT measured by Ohmmeter ) . Comment on the graph.

7- Connect R2; R3 in parallel and repeat steps 3. Record the data in Table.4 below:

8- Draw I-V curve using the data from the above table Table.4. Plot the current on the y-axis and the voltage in the x-axis. Find the slope of the straight line and compare it with the value of RT ( RT measured by Ohmmeter ) . Comment on the graph.

Data:

Table1

Resistors
Listed value
Ohmmeter Value
Multisim Value
R1
1.0k?
0.994 k?
1.0k?
R2
2.2k?
2.199 k?
2.2k?
R3
3.3k?
3.360 k?
3.3k?

Table2

Vs
2.0v
4.0v
6.0v
8.0v
10.0v
12.0v
2.06mA
4.13mA
6.19mA
8.20mA
10.27mA
12.41mA
Multisim I
2mA
4mA
6mA
8mA
10mA
12mA
Calculation I
2mA
4mA
6mA
8mA
10mA
12mA

Table3
Vs
2.0v
4.0v
6.0v
8.0v
10.0v
12.0v
0.37mA
0.72 mA
1.09 mA
1.46 mA
1.82 mA
2.18 mA
Multisim I
0.363mA
0.727mA
1.091mA
1.455mA
1.818mA
2.182mA
Calculation I
0.363mA
0.727mA
1.091mA
1.455mA
1.818mA
2.182mA

Table4
Vs
2.0v
4.0v
6.0v
8.0v
10.0v
12.0v
1.55mA
3.08 mA
4.62 mA
6.16 mA
7.65 mA
9.20 mA
Multisim I
1.515mA
3.03mA
4.545mA
6.06mA
7.575mA
9.09mA
Calculation I
1.515mA
3.03mA
4.545mA
6.06mA
7.575mA
9.09mA

Sample calculated value:

TABLE2:

V=2V

TABLE3:
=3.3 V=2V

TABLE4:
=3.3 V=2V

= 1.32k?

Multisim:

Analysis:

There’s only less percentage of error in the current because we use the multitier to measure the exact value of resistance and voltage. We prove the ohm’s law and get the relationships between the current and voltage as we can see from the graphs above we get a linear line that prove that the voltage across a conductor between to point’s is directly proportional to the current.

Conclusion

To sum up, In this experiment I learned how to connect the resistance in two way in parallel and series.We prove the Ohm’s Law . However, a few mistakes were made in our experiment. Such as, the Multimeter was not working well and the wires was not connected. However, we end up the experiment successfully and we achieve all the objectives.

References
Multisim
Wikipedia
Circuit lab manual

Review questions:

1. Three resistors are connected in parallel across 50V , the values of the resistors are 620? , 750 ? and 1200 ? :

a. What is the value of the total current?
I=V/R
I=?
V=50V
RT = = 264.58 ?
I=50V/264.58 ?
I=188.98mA

b. If one of the resistors were shorted, what would you expect to see happen?
Short will cause a direct circuit path between the negative and positive terminal leads of the power supply. So the wire would get very hot and maybe melt open or burn the insulation.
2. What is the difference between the value of RT if the resistors are connected in series and value of RT if the resistors are connected in parallel.

-RT when we connected the resistors in series is larger than the largest resistor
-RT when we connected the resistors in series is less than the smallest resistor

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