TITLE : Kirchoff Law

OBJECTIVES

i. Explore series and parallel combination of resistors

ii. Measure the resisitor value using digital multimeter

EQUIPMENT LIST

Multimeter DC Power Supply

Bread Board Wire Clip

Resistors

THEORY

From the experiment given so far , it should be easy for you to identify both

series and parallel circuits. But there is another type of circuit that has branches, like

parallel circuit, and series loads or elements like series circuit. This is called a series-

parallel network since it is a combination of the others

There are many circuits that are so complex that they cannot be solved by

Ohm’s Law’s. There circuits have many branches or many power sources, and Ohm

Law’s would be either impractical or experiment of a German physicist. Gustaw

Kirchoff. About 1897, Kirchoff developed two conclusions, known as Kirchoff’s

Law, can be state as follow :

Kirchoff’s Voltage Law

Kirchhoff’s voltage law is also known as his first law. It is stated that he sum

of the voltage drop around any closed loop is equal to the sum of the voltage source in

that loop. It gives the relationship between the voltage drops around any closed loop

in a circuit and the voltage source in that loop. The total of the two quatities are

always equal. This can be given in equation form as : ΣV 5=Σ IR, where the symbol

Σ which is the Greek letter sigma, means “the sum off”.

Kirchoff’s Current Law

Kirchoff’s current law is called his second law. It is started that the current

arriving at any junction point in a circuit is equal to the current leaving that point.

Current cannot collect or buit up at a point. Thus if 1A of current arrives at a junction

that has two parths leading away from it, it will divide among the two paths , but the

toal 1A must leave the junction.

INTRODUCTION

The circuits in this problem set are comprised of unspecified circuit elements. (We

don’t know if a particular circuit element is a resistor or a voltage source or something

else.) The current and voltage of each circuit element is labeled, sometimes as a value

and sometimes as a variable. Some of these problems ask that we determine the value

of a particular voltage or current. Other problems ask for the values of the power

supplied or received by a particular circuit element. Kirchhoff’s laws are used to

determine values of currents or voltages. The passive convention is used to decide if

the product of a particular element current and voltage is the power supplied or

received by the circuit element

EXPRIMENT 9-1

Kirchhoff’s Voltage Law

1. The circuit as per figure 9-1 using variable DC Power supply, bread board ,

multimeter, resistors and wires provided.

2. Turn on the variable power supply. Adjust the power supply to 20V

3. Measure and record the VR1 as indicated by the volimeter at the moment the

voltage is applied

VR1 = 4.41 v

4. Turn off the power supply. Remove the voltmeter lead’s from R1 and place

across R2 as per figure 9-2. Measure and voltage VR2

VR2 = 6.63

5. Turn off the power supply. Remove the voltmeter leads from R2 and place

them across R3 as per figure 9-3. Measure and record voltage VR3

VR3 = 8.92 v

6. Calculate Vtotal = VR1 + VR2 + VR3

= 4.41 + 6.63 + 8.92

= 20 V

7. Is Vsupply = Vtotal ? YES

Explanation : Because the total of voltage drop equal to volatage supply.

EXPERIMENT PROCEDURE 9-2

Kirchhoff’s Current Law

1. Set the circuit as per figure 9-4 using variable DC Power supply, bread board,

ammeter, resistor and wires provided . ote that 3 load resistors connected in

parallel. (The same ammeter will be used to measure the current through each

of the 3 resistors).

2. Turn on the variable power supply. Adjust the power supply to 20V

3. Measure and record the Isupply as indicated by the ammeter

I supply = 40mA

4. Turn off the power supply. Reconnect the circuit as per figure 9.5

5. Turn on the power supply. Measure and record the I1 as indicated by the

ammeter

I1 = 20 mA

6. Turn off power. Reconnect the circuit as per figure 9-6

7. Turn on the power supply. Measure and record the I2 as indicated by the

ammeter

I1 = 13 mA

8. Turn off the power supply. Reconnect the circuit the circuit as per figure 9-7

9. Turn on the power supply. Measure and record the 13 as indicated by the

ammeter

I3 = 10 mA

10. Turn off the power supply. Calculate Itotal = I1 + I2 + I3

= 20 mA + 13mA + 10mA

= 43 mA

11. IS Isuply = Itotal ? NO

Explanation :

This is because there an error occur due to the multimeter with 0.003A

difference.

DISCUSSION

Kirchhoff’s Voltage Law is a useful tool for circuit analysis.

The voltage drops across both resistors were equal even though the currents

were different. The voltage drop is ALWAYS the same across two resistors

in parallel.

Notice that IR1 + IR2 = I. This means that current is conserved. We will learn

later that this is an application of Kirchhoff’s Current Law (KCL)

CONCLUSION

The conclusion of this experiment proves that Kirchoff Law’s is true. The sum of the

currents flowing through the branches of a parallel circuit will be equal to the current

flowing through the sum branch of a circuit.

REFRENCES

1. http://www.slideshare.net/itsnadia/physics-experiment

2. http://www.ampbooks.com/home/tutorials/lesson-007/

3. Lab sheet 9

4. Circuit Theory / Kirchoff Law’s

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