Basic Electrical & Electronics Engineering (BT-104)
EXPERIMENT NO. 1
OBJECTIVE: Perform experiment to verify Kirchhoff’s laws.
For network analysis Kirchhoff’s Voltage law forms the basis on which different theorems and
corollary are developed,
APPARATUS REQUIRED:
1. Trainer Kit (Made of MARS, Model No. ME561P)
2. Multimeter & Connecting ports
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. (5Ω, 10Ω, 22Ω & 33Ω) are mounted
on front panel.
3. Circuit for Kirchhoff laws is engraved on front panel.
4. Two Digital Panel Meter (DPM) are provided on the front panel to measure
corresponding Voltage & Current with connections brought out on sockets.
Specifications of Meters
Type Parameter Range Resolution Accuracy
3.5 Digit DPM DC Voltage 0-20V DC 0.01V DC 0.5% + 2 Digits
3.5 Digit DPM DC Current 0-2 A DC 1 mA DC 0.5% + 2 Digits
KIRCHHOFF’S VOLTAGE LAW:
THEORY:
The algebraic sum of the voltages around any closed path is zero consider closed loop ABC
In clockwise direction starting from point A
the algebraic sum of the voltage is
VAB + VBC – VT = 0
(Exp. no. 1)1
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In determining the algebraic sign of voltages, first mark the polarity of each voltage as
shown above.
Now go round closed path and consider any voltage whose plus terminal is reached first as
positive & whose negative terminal is reached first as negative)
Thus in above closed loop starting from A, clockwise,
VAB is positive
VBC is positive
VT is Negative
There by VAB + VBC – VT = 0
PROCEDURE:
1. Make the connection by joining the points A-B, C-D, E-F, G-H and Ammeter terminals
using patch cord, Fig.2.
2. Switch ON the power supply, then for KVL verification we have to take mesh made
using R1, R2, R3, and R4.
3. Measure the voltage across each resistor one by one using Digital Multi Meter (DMM).
Note down these readings along with polarity.
(Exp. no. 1)2
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OBSERVATION TABLE:
Calculation for
mesh (R1-R2-R3- Write
comment
R4) to verify
based on
KVL by using answer come
equation VR1+ in left the
column
VR2 VR4 VR3 =
Expected theoretical answer:
Algebraic sum of the voltage over a mesh (R1-R2-R3-R4) should be zero. i.e. VR1+ VR2 VR4
VR3 =0, hence result is verified.
Comments on above Reading of Observation Table: If the reading in second last column is zero, it means the law has been
verified (Comment: Hence the law is verified) otherwise the value calculated in the second last column is containing some error
due to instruments (Comment: The value calculated is due to instruments error).
Note: Write only comment in the last column that applicable for your case.
KIRCHHOFF’S CURRENT LAW:
THEORY:
The algebraic sum of the current entering and leaving any point in a circuit must
equal zero or stated another way the algebraic sum of the currents into any points of the circuit
must equal the algebraic sum of the currents out of that point
An algebraic sum means combing positive and negative values.
All currents into a node is positive and all currents directed away from that point is negative.
(Exp. no. 1)3
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For a given node a I1 and I2 is positive as they are into the
node a and I3 is negative as it is out the node for node a we
can write the equation
As I1 + I2 – I3 = 0
We can rewrite the above equation as I1 + I2 = I3
i.e. current into node A = current out from node A.
Kirchhoff’s current law is really the basis for the practical rule in parallel circuits that the total
line current must equal the sum of branch current.
IL = I1 + I2 + I3
PROCEDURE:
1. Since we are going to verify KCL in circuit for taking node ‘D’or ‘H’ because both nodes are
same. This node connected with three conducting path. So we have to measure three currents.
2. Make the connection by joining the points A-B, C-D, E-F, G-H and Ammeter terminals using
patch cord, Fig.2.
3. Note down the reading of ammeter and also mark the direction of current (this current is
defined as supply current IS), if meter reads positive reading, it meant that current is entering
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from red terminal of ammeter and exit from black terminal of ammeter. If meter show
negative value then it meant that current is exiting from red terminal of ammeter and enter
from black terminal of ammeter.
4. Now make the connection by joining the points A-B, E-F, G-H and Ammeter between C-D
terminals using patch cord for measuring another current associated to this node, Fig.4.
5. Note down the reading of ammeter and also mark the direction of current (this current is
defined as IR2), if meter reads positive reading, it meant that current is entering from red
terminal of ammeter and exit from black terminal of ammeter. If meter show negative value
then it meant that current is exiting from red terminal of ammeter and enter from black
terminal of ammeter.
6. Now make the connection by joining the points A-B, E-F, C-D and Ammeter between G-H
terminals using patch cord for measuring last current associated to this node, Fig.5.
7. Note down the reading of ammeter and also mark the direction of current (this current is
defined as IR4), if meter reads positive reading, it meant that current is entering from red
terminal of ammeter and exit from black terminal of ammeter. If meter show negative value
(Exp. no. 1)5
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then it meant that current is exiting from red terminal of ammeter and enter from black
terminal of ammeter.
8. The above process can also follow to verify the Kirchhoff’s current law at any other node.
The verification of the law can be done by students practically without lodging the readings
in the observation table.
OBSERVATION TABLE: KCL VERIFICATION AT NODE D or H:
Calculate IR2+IR4IS to verify KCL Write comment based on answer come in left the
(consider “+ sign” for current enter at node) column
Expected theoretical answer:
Algebraic sum of the current at node (D or H) should be zero. i.e. IR2+ IR4 IS =0, hence
result is verified.
Comments on above Reading of Observation Table: If the reading in left column is zero, it means the law has been verified
(Comment: Hence the law is verified) otherwise the value calculated in the left column is containing some error due to
instruments (Comment: The value calculated is due to instruments error).
Note: Write only comment in the last column that applicable for your case.
(Exp. no. 1)6
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PRECAUTIONS:
(1) Make sure that all the electrical connections are correct before switching any circuit.
(2) Switch on the supply, only after getting the circuit checked by the proper person guiding
the experiment.
(3) All the connections made as per the circuit diagram.
(4) Choose the Instruments of appropriate rating.
Note: 1. All write-up which is enclosed by rectangular box in this laboratory manual will be
written on pages without lines at appropriate location using pencil only.
2. Rest other write-up of this laboratory manual will be written on pages with lines by blue and
black for headings.
3. Both side of pages will be utilized
4. Write the next experiment write-up from fresh page.
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