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VERIFICATION OF KIRCHHOFF'S LAW KCL & kK

inction

OBJECT
T o verify the Kirchhoff's Current Law.
2 To verify the Kirchhoff's Voltage Law.

APPARATUSREQUIRED
1.
Experimental kit fitted with:
(a) Voltmeter 0I No.
(b) Milli Ammeter 02 Nos.
(c) Variable DC Voltage Source 02 Nos.
(d) Patch Cords

THEORY

KIRCHOFF'S CURRENT LAW (KCL)

I t states that the algebraic sum of currents mecting at a junction of conductors

is zero. In other words, the sum of the currents flowing away from a junction is equal

to the sum of currents flowing towards the junction. 7

The law is illustrated in Fig 1 ' where in ithere are six currents I, l2, I, I4, Is.

and Is meeting at a junction. Assuming the currents entering into the junction as

the negative, we can take the algebraic

positive and currents leaving junction as sum

of all of these six currents and equate it to zero

I+12+1,+l4-Is-I,=0

shorthand was as
written in
This equation can be a

j=1
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Alternatively, we can write KCL as the sum of currents

flowing towards the
junction equal to the sum of currents
flowing away from the junction. Thus,

Kirchoff's Current Law is

nothing more than a restatement of principal of
conservation of charge. Since the
accumulation of electric charge at a junction is not
possible, the amount of
charge entering a junction at an instant must be the same as
the amount of charge
leaving the junction.

/1s

Fig-1': Illustration of Kirchoffs Current Law

KIRCHOFF'S VOLTAGE LAW(KVL)

t states that at any time instant the algebraic sum of voltage around a closed
circuit or a loop is zero. That is, for a closed circuit having k elements,

k
V, = 0
j1
of the j" element. Above equation is just
Where Vi represents the voltage drop
a shorthand statement of:-

V+V2+V,+..+V =0
2
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This statement simply tells us that if we start from a particular junction and.go
around a closed circuit so as to come back to the same junctiom, the net potential dro
back to the point at the same
(or potential rise) is zero, because we have come

the KVIL equation for a circuit, attention should be paid to

potential.While writing
the algebraic sign of the voltage across each element.

In any closed circuit the algebraic

Kirchoff's voltage lawcan also be stated as:
to the
products of current and resistance in each of the conductors equal
Sum of the is

algebraic sum of the emfs of the batteries.

We may apply KVL to a circuit in several different ways. Often students

commit error while writing KVL equation for a closed circuit. Viewing KVL, as

in above equation leads to fewer errors that other statements.

given

VR

b) A Battery
(a) A Resistor

Fig-2': Polarity of Voltage

mark the polarity of the voltage across each
To apply KVL, you should first
the assumed direction of current. As
element. In resistor, the polarity depends upon
a
marked as positive, the
which the current enters is
shown in Fig 2'(a) the end into
Note that, as shown in Fig
end from which the current leaves is marked as negative.
across a battery does not depend upon the
2'(b) the polarity of the voltage (emf)
the circuit.
assumed direction of current flowing through

around the
Now you can write the KVL equation simply by moving nentally
anticlockwise, if you so wish) direction aud
closed circuit in a clockwise (or in an

element whose (+) terminal is entered and

of each
writing down directly the voltage
of every voltage frst met at (-) sign.
writing down the negative
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R2 22092

w
A R 3302

A w
Rg 4702

Fig-3'

KIRCHOFF'S CURRENT LAW

PROCEDURE
Connect the different instruments and equipment as shown in Fig 3°'.
)
in anti-
(i) Set the voltage source to minimum position by rotating the knob
clockwise direction.

(ii) Switch ON supply.

Increase the source voltage and note down the reading of ammeters A,
(iv)
Az & As
different setting of source voltage.
(v) Repeat step 4 for
with different value Ri,
Repeat step 4 and step 5 by constructing circuit
(vi)
R and R

OBSERVATION

table-1
Record the Observation as per

Table-1: Az t As
A2 Az
S No. A mA) (mA)
(mA) mA) 1.00
7.43 3.57
1. 11.00

4
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2.58 7.96
8.00 5.38
2 14.95
4.85
15.00 10.10
3.

in column 2 and (A + A) in colomn 5 of table-I should be

Check the entry A of accuracy
Cqual. Minor difference in values
of A and (A, t+ A), if any, is because
level of instruments

KIRCHOFF'SVOLTAGE LAW
PROCEDURE(a)
and equipment as shown in Fig 4'.
) Connect the different instruments
knob in anti-
Set the voltage source to minimum position by rotating the
(i)
clockwise direction.

(ii) Switch ON supply.

down the reading of Voltages
Increase the source voltage and note
(iv)
across E, Ri, R2 & R3.
difierent setting of source voltage.
(v)
(v) Repeat step 4 for
values of
circuit with different
Repeat step 4 and step 5 by constructing
(vi)
R, R2 and R.

R-330s2
R 2202

R-4702
E

Fig-4
 OBSERVATION (a)
Record the observations in
table -2.
Table-2:
S No. E
R R2
R3VRIVR VRs V Loop
1. 6.91
(VR+ VR2 Voltage
220 330 +VR3) (E- V)
470 1.48
2. 9.82 220
2.25 3.17 6.90 0.0i
330 470 2.11 3.21 4.50 9.82 0.00

Loop voltage should be zero. Non-zero

level of instruments. value, if any, is because of accuracy

PROCEDURE(b)
) Connect the different instruments and
equipment shown in
as
Fig '5.
(i) Set the voltage sources to minimum position by rotating the knob in
anti-clockwise direction.

ii) Switch ON supply.

(iv) Increase the source voltages and note down the reading of Voltages
across E, E2, Ri, R2 &R3.

(v) Repeat step 4 for different setting of source voltages.

( Repeat step 4 and step 5 by constructing circuit with different values of

Ri, R2 and R3.
 ORPORATHON

R=2202 f|,
R=3302

+
R-4702

Fig-5
OBSERVATION (b
Record the observations in table -3.

Table-3:
S E1 E 2 E R1 R2 R3VRI| VR2 VR3 V Loop
No. (E1-E2)
(VR1+VR2 + Voltage
VR3) (E--V)
1. 9.84 4.85 4.99 220|330 470 1.07 1.63|2.29 4.99 0.00

because of accuracy
Non-zero vaBue, if any, is
Loop voltage should be
zero.

level of instrumentS.

PROCEDURE(c)
and equipment as shown in Fig "6'.
) Connect the different instruments
the knob in
sources to minimum position by rotating
(ii) Set the voltage
anti-clockwise direction

(ii) Switch ON supply.

reading of Voltages
and note down the
Increase the source voltages
Civ)
across E, Ez, Ri, R2 & R3.
voltages.
different setting of
source

(v) Repeat step 4 for

7
 (vi)
(Vi) Repeat step 4 and step 5 by constructing circuit with different va
R, R2 and R3.

R2202 R=3302

E R-470

Fig-6'
OBSERVATION (
Record the observations in table -4.

Table-4:
SEIE2 E RI R2 | R3 VR1|VR2 VR3 V Loop
No. (E1+E2) (VRI +VR2+ Voltage
VR3) (E V)
.9.90 4.4714.37 220 | 330 470 3.09 4.69 6.59 14.37 0.00

Loop volage should be zero. Non-zero value, if any, is because of accuracy

level of instruments.

Note Reading in the all above tables are sample readings/calculation. The
vaiues may differ for different setups.
 TO STUDY KIRCHHOFF'S LAW (KCL & KVL)
65 X 32 MM 65X 32 MM 65 X 32 MM
TO BE CUT TO BE CUT TO BE CUT

V mA mA O

R
Ri A w-o
220
- AoWW- R
Vs 330 330 2
ow 470 2

DC VOLTAGE
SOURCE KCL
R1 Ra
OO -0-
220 2 330 Q
-
POTENTIOMETER
Vs 470 2R
O
-MAIN FUSE
KVL