VERIFICATION OF

KCL & KVL

APPARATUS

USER’S MANUAL

PAGE NO. : 1/ 4

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 OBJECTIVE : Verification of KCL and KVL Apparatus has been designed to calculate the value of current
flowing through different branches of the circuit.

The instrument comprises of the following built in parts:

1. DC Regulated Power Supply of 0-3V.

2. Four type of wire wound resistances, each of 5watt. (5, 10, 22 & 33) are mounted on front panel.

3. Circuit for Kirchhoff laws is engraved on front panel.

4. Two round meters are mounted on front pannel to measure corresponding voltage and current.

THEORY
i5 i1

In simple circuits,the resistance and potential difference are calculated with the i2
help of ohms law. But in actual practice, we come across complicated circuits
i4
which contain a large number of resistances alongwith several sources of e.m.f. In i3
such cases, the effective resistance and the e.m.f. can not be calculated easily
from ohm’s law. In order to solve such networks, Kirchhoff gave two laws which are i1- i2- i3 + i4 + i5 = 0
or
known as Kirchhoff’s laws.
i1+ i4 + i5 = i2 + i3

First Law :
According to Kirchhoff’s first law. “The algebriac sum of the various currents meeting at a
junction in a closed electrical circuit is Zero.

Sign Convention :
The currents flowing towards a junction are taken as positive while the currents
flowing away from the junction are taken as negative. Let us consider a junction 0. Where a number of conductors
meet. i1, i2, i3, i4 and i5 are the currents flowing through them in the directions shown in Fig. (1). Applying
Kirchhoff first law, we get.
B
Thus the total amount of R1 R2
i1 5 10
current flowing into a junction I
must be equal to the total current A
C
flowing out of the junction. Clearly, I2
R3 R4 I = i1 + i2
according to this law, electric INPUT
+ 22 33 D
VOLTAGE
current cannot accumulate at any 2.5V DC -
point. Unlike charge, current
cannot be stored. It must flow on.
Fig. (1)
PAGE NO. : 2/ 4

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 Second law :
According to second law, in a closed loop (closed circuit or mesh) the algebriac sum of the emfs is equal
to the algebric sum of the products of the resistances and the respective currents flowing through them.

The distribution of currents in the circuit is shown in the diagram given below according to Kirchhoff’s
first law.

NOTE : Resistance tolrance is in +10%.

PROCEDURE

For calculation of i1 current : B

R1 R2 +
i1 5 10 MA
Connect the circuit as
I -
shown in Fig. (1a) i.e. connect current A
C
meter (mA) across B and C point as
R3 R4 i1
shown while C and D points will INPUT + 22 33 D
VOLTAGE
remain open.
2.5V DC -

Applying Kirchhoff’s second law to

the closed mesh A B C A, We get Fig. (1a)

5i1+10i1 = 2.5
15i1 = 2.5
i1 = 2.5 /15 amp
i1 = 166.66 mA. (Calculated value)

Compare this calculated value to observed value at current meter :

Calculation of i2 current : B
R1 R2
5 10
Connect the circuit as shown in I
A -
Fig. (1b) i.e. connect current meter (mA) C
across C and D point as shown while B I2 R3 R4 MA I2
INPUT + +
22 33 D
and C point will remains open. VOLTAGE
2.5V DC -
Applying Kirchhoff’s second law
to the closed mesh A D C A, we get Fig. (1b)

PAGE NO. : 3/ 4

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 22 i2 + 33 i2 = 2.5
55 i2 = 2.5
i2 = 2.5/55 amp
= 45.45 mA. (Calculated Value)

Compare this calculated value to observed value at current meter.

Calculation of total current i : R1 R2 B

i1 5 10
I
Connect the circuit as A
C
shown in Fig. (1c) i.e. connect I2
R3 R4 I = i1 + i2
point B C and D. Also connect INPUT + 22 33 D
VOLTAGE
current meter (mA) between -ve 2.5V DC -
terminal of battery and point C.
- MA
+
Total Current Fig. (1c)
i = i1 + i2
i = 166.66 + 45.45
= 212.11 mA (Calculated value)

Compare this calculated value to observed value at current meter.

STANDARD ACCESSORIES

1. Single Point (4mm) Patchcords for Interconnections. : 10 Nos.

2. Instruction Manual. : 1 No.

PAGE NO. : 4/ 4

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