POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
EXPERIMENT 2
PART A
TOPIC
:
OHM’S LAW
OBJECTIVES :
At the end of this experiment, students should be able to :
i.
Use the power supply unit correctly.
ii.
Measure the current that flow through the resistor using the ammeter
correctly.
iii.
Measure the voltage across the resistor using the voltmeter correctly
iv.
Understand the theory of simple direct current (DC) circuit connection.
v.
Determine the relation between voltage and current in a circuit
THEORY
OHM’S LAW
Ohm’s Law states that the electrical current (I) that flows through a resistor (R) is proportional
with the differential force (V) across the resistor; under one condition which is the temperature is
unchanged.
Therefore: Ohm ‘s Law is:
V  I
V
= Constant
I
The constant parameter is resistance (R)
Which is R =
V
I
V in volt, I in ampere and R in ohm ()
EQUIPMENTS :
i.
ii.
iii.
iv.
v.
vi.
Variable resistor
Ammeter
Voltmeter
Multimeter
Power Supply Unit
Cable
PROCEDURES :
1. Set the resistor at 50 ohm.
2. Set the power supply at minimum.
3. Connect the circuit as shown in Picture 1.1 ( make sure that all the meter is connects
correctly : ammeter – series, voltmeter – parallel)
___________________________________________________________________
1
POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
R
A
V
Picture 1.1
4.
5.
6.
7.
Increase the supply voltage and measure the current in the circuit.
Take note the values and fill it in the Table 1.2
Reset the voltage to minimum and replace the resistor from 50 ohm to 100 ohm.
Repeat steps 4 and 5 and fill the result in Table 1.3.
Result:
Resistor : 50 
VOLTAGE SETTING
CURRENT VALUE
0V
3V
6V
9V
12 V
TABLE 1.2
Resistor : 100 
VOLTAGE SETTING
CURRENT VALUE
0V
3V
6V
9V
12 V
TABLE 1.3
___________________________________________________________________
2
POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
Discussion :
1. What is the relation between voltage and current
…………………………………………………………………………………………………
…………………………………………………………………………………………………
……………………………………………………………………………………………….
…………………………………………………………………………………………………
…………………………………………………………………………………………………
2. State the Ohm ‘s Law and its’ relation to this practical.
…………………………………………………………………………………………………
…………………………………………………………………………………………………
………………………………………………………………………………………………..
…………………………………………………………………………………………………
………………………………………………………………………………………………..
3. Analyse V, I and R from the practical result and compare it with the theory that you
have learn.
Resistor : 50 
Resistor : 100 
___________________________________________________________________
3
POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
Current value ( I ) from calculation :
RESISTOR 50 
RESISTOR 100 
Conclusion :
Give your conclusion from the experiment.
………………………………………………………………………………………………………
…………………………………………………………………………………………………….
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
…………………………………………………………………………………………………….
………………………………………………………………………………………………………
___________________________________________________________________
4
POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
EXPERIMENT 2
PART B
TOPIC : CURRENT AND VOLTAGE MEASUREMENT IN SERIES CIRCUIT
OBJECTIVES:
At the end of this experiment, students will be able to:
i.
ii.
iii.
iv.
v.
Determine the total series resistance in the serial circuit.
Measure the current flow in the circuit.
Measure the voltage drop each resistors in the circuit.
Prove that the current flow is the same in all parts of the circuit
Prove that the algebraic sum of the voltage drops across each resistor
must equal the algebraic sum of the applied voltage
THEORY OF SERIES RESISTIVE CIRCUIT
Resistors are said to be in series when they are connected in such a way that there is only one
path through which current can flow. This means that the current in a series circuit is the same
in all parts of the circuit.
The voltage drop across each component in a series circuit is dependent upon the current level
and the component resistance.
Based on Ohms Law
I
V1 = IR1 , V2 = IR2 , dan
V1
R1
VJ = IRJ
The total voltge drops VJ = V1 + V2
substitute V with IR
V
IRJ = IR1 + IR2
R2
V2
Divide the equation with I
hence
R J = R 1 + R2
RJ is the total series resistance
Series ci rcuit
I
Two series connected resistors are shown in the figure above, together with a battery to supply
e.m.f and current. It is seen that the resistors are connected end to end in such a way that there
is only one path through which current can flow.
___________________________________________________________________
5
POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
EQUIPMENTS:
i.
ii.
iii.
iv.
v.
resistors
miliampere
voltmeter
power supply
cable
PROCEDURE:
1.
Setting the value of resistor to R1 = 70Ω R2 = 50 Ω and R3 = 100 Ω.
2.
Construct the circuit as shown in the figure below.
3.
Set the power supply to 10V.
4.
Measure the current flow through A ( I1 ), B ( I2 ), C ( I3 ) and D ( I4 ).
Record the result in table.
[ ensure that the meters are connected correctly : ammeter – series,
meter volt – parallel ]
5.
Measure the voltage drops across each resistor, R 1 , R2 and R3. Record
the values in the table.
RESULTS
RESISTANCE (Ω)
CURRENT ( mA )
VOLTAGE ( V )
R1
I1
V1
R2
I2
V2
R3
I3
V3
RT
IT
VT
___________________________________________________________________
6
POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
DISCUSSION :
1.
Determine the current that flows through point A, B , C and D. What is your
comment?
…………………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………………..
2.
Compare the V1, V2, V3, VT. Comment on your answer.
…………………………………………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………………………..
3.
Calculate the value of V1, V2 , V3, and VT, I1, I2, I3 and IT , RT by theory .
V1, V2 , V3, and VT
I1, I2, I3 and IT
RT (Total Resistance) =
___________________________________________________________________
7
POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
4. Discuss the results obtained from the experiment comparing with the answer from the theory
that you have learnt .
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
CONCLUSION:
Give the conclusion from experiment.
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
___________________________________________________________________
8