Experiment 3 Ohm’s Law and Resistance

By: Aisha Ali Sulaiman Mohamed Alnaqbi H00367954

Partners: Alya Mohamed Ali Omani Alnaqbi H00351803 Ghayah Mohammed Karam Jalal Alkaabi H00368030

Class: 15356

For: Mr. Wassel Al Abbas

Date: 18/10/2018

INTRODUTION:-

Objective:

1-This experiment will show the relationship between the voltage(V) , resistance(R) and current(I) in a circuit

2-prove the Ohm’s Law.

3-Find the total resistance for series and parallel connection circuit

Theory:

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:-

total resistor in a series circuit

R = R1 + R2 + R3…..Rn

total resistor in a parallel circuit

R=(??R1?^(-1)+?R2?^(-1)+?R3?^(-1)+?Rn?^(-1)…)?^(-1)

we have to connect the Ammeter in series to measure the current

we have to connect the Voltmeter in series to measure the voltage

Material and equipment:

Varied values of resistors

Power supply

Power supply cables

Connecting wires

Multimeter

Breadboard

Jumper wires

Experimental set up and Procedure:

Measure using Multimeter the resistance of the three resistors listed in the table below Table.1 .

Use breadboard to connect R1 = 1.0 k into the circuit as shown in Fig.

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.

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. ?

Replace R1 with R2 & R3 connected in series and repeat steps 3. Record the data in Table.3 ?

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. ?

Connect R2& R3 in parallel and repeat steps 3. Record the data in Table.4 below: ?

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

Breadboard I 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

Breadboard I 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

Breadboard I 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:

The result of calculate the current when the voltage is 2V and the R_1=1k?

R_1=1k? V=2V

I=V/R=2/1=2mA

The result of calculate the total resistance ?(R?_T) when R_2=2.2k? and R_3=3.3k? connected in series:

R_2=2.2k? R_3=3.3 k? V=2V

R_T= R_2+R_3

R_T=2.2+3.3=5.5k?

The result of calculate the current when the voltage is 4V and R_2=2.2k? and R_3=3.3k? connected in series:

I=Vtotal/Rtotal=4V/(5.5K?)=0.727mA

The result of calculate the total resistance ?(R?_T) when R_2=2.2k? and R_3=3.3k? connected in parallel:-

R_2=2.2k? R_3=3.3 k? V=2V

R_T=(??R_2?^(-1)+?R_3?^(-1))?^(-1)

R_T=(??2.2?^(-1)+?3.3?^(-1))?^(-1) = 1.32k?

The result of calculate the current when the voltage is 4V and R_2=2.2k? and R_3=3.3k? connected in parallel:

I=Vtotal/(R totl)=4V/(1.32K?)=3.03mA

Multisim:

Measure the resistance in the resistor:-

Measure the Current on 1.0K? resistor:-

Measure the Current on 2.2k? resistor and 3.3k? resistor connected in series

Measure the Current on 2.2k? resistor and 3.3k? resistor connected in parallel

Analysis:

There’s only less percentage of error in the solutions because when we find the voltage and the current in the multimeter we didn’t but the exact value .

Conclusion

to sum up, Ohm’s law can used in both parallel and series circuits. In parallel circuits , there are more than one path each bath has same voltage while the current is different . on the other hand In series circuits , there is only one path which has same current and different voltage.

References

Multisim

Wikipedia

Circuit lab manual

Review questions:

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

What is the value of the total current?

I=V/R

I=?

V=50V

RT = ? (?620?^(-1)+ ?750?^(-1)+?1200?^(-1))?^(-1) = 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