KIRCHOFF’S LAW

IntroductionIntroduction

Ohm's Law described the relationship between current, voltage, and resistance. These circuits have been relatively simple in nature.

Many circuits are extremely complex and cannot be solved with Ohm's Law. These circuits have many power sources and branches which would make the use of Ohm's Law impractical or impossible.

Kirchhoff’s Law is an important algebraic in solving the currents and voltages of the circuit.

DefinitionDefinition

Node – A point or junction in a circuit where two or more components connect.

Loop – A closed path in a circuit.

Voltage drop – The voltage between any two specific points of an electrical conductor.

Branch – A single or group of components such as resistors or a source which are connected between two nodes.

PartsParts

Kirchhoff can be divided into two parts:

Kirchhoff’s Current Law (KCL)

Kirchhoff’s Voltage Law (KVL)

Kirchhoff’s Current Law (KCL)Kirchhoff’s Current Law (KCL)

Kirchhoff's current law states that the algebraic sum

of the currents entering at a node (i.e., any junction of

wires) equals the sum of the currents leaving that node.

Or the algebraic sum of all currents at any node

in a circuit is equal to zero.

I1

I2 I3

Current In = Current Out I 1 = I 2 + I 3 i.e. I 1 + (- I 2 ) + (- I 3 ) = 0 = 0

Hukum Kirchoff ArusJumlah algebra arus yang memasuki

sebarang titik persimpangan atau nod di dalam litar elektrik adalah bersamaan dengan jumlah algebra arus yang keluar dari titik persimpangan tersebut.

Kirchhoff’s Current Law (ExampleKirchhoff’s Current Law (Example))

I1 = 2A

I5 = 1A

I2 = 5A

I3

I4 = 3A

Refer to the figure above, calculate current I3.

Kirchhoff’s Current Law (ExampleKirchhoff’s Current Law (Example))

Solution

Current entering node : I1 = 2A , I2 = 5ACurrent leaving node : I3 = ?, I4 = 3A, I5 = 1A

Using Kirchhoff’s Current Law, Current entering node = Current leaving node

I1 + I2 = I3 + I4 + I5

I3 = I1 + I2 - I4 - I5

= 2 + 5 - 3 - 1 = 3 A

Kirchhoff’s Voltage LawKirchhoff’s Voltage Law

Kirchhoff‘s Voltage Law states that the sum of voltage

drop is equal to the total source voltage.

Or the algebraic sum of voltage source and voltage

drop in a circuit is zero.

Voltage equation

VS = VR1 + VR2 + VR3

or

VS – VR1 – VR2 – VR3 = 0

R1

I

VS

R3

VR1

VR3+-

VR2

+ - +-

R2

Hukum Kirchoff VoltanDalam sebarang litar elektrik yang

lengkap jumlah algebra bagi d.g.e mestilah bersamaan dengan jumlah algebra kejatuhan (susut) voltan pada perintang dalam litar (gelung) tersebut.

Kirchhoff’s Voltage Law (Example)Kirchhoff’s Voltage Law (Example)

R 1

I

V S

R 3

V R 1 = 4 V

+-

+ - +-

R 2

V R 3 = 6 V

V R 2 = 8 V

Refer to the figure above, calculate the voltage source VS..

Kirchhoff’s Voltage Law (Example)Kirchhoff’s Voltage Law (Example)

Solution

Using Kirchhoff’s Voltage Law

VS – VR1 – VR2 – VR3 = 0

VS = VR1 + VR2 + VR3

= 4 + 8 + 6

= 18 V

Example 1

Find the current value of I1, I2 and I3

R 1= 5Ω R 2=2 Ω

R 4= 4 ΩR 3=3 Ω

I2

I3

I1

E = 12 v

Loop 1 Loop 2

Example 2

Find the current through the resistor 120 Ω,

240 Ω ND 200 Ω by using Kirchoff Law.

E1 = 6V

R1 = 120 Ω

E2 12 V

R2 = 240 Ω

R3

200 Ω

+

-

+

-

Example 3Refer on the below diagram find the value of : -

Currents I1, I2, I3, I4 and I5 using Kirchhoff’sLaw.

1I

20

10V

20

10040

100

I2

I3I1

I4

I5

Thank You