Title:
To Measure The Power Of Resistance Load.
Objective:
To measure the voltage, current and power in a single-phase circuit with Resistive load.
Apparatus:
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5 resistor of different values.
DC variable power supply.
Voltmeter
Ammeter
Bredboard
Theory:
Resistance:
Resistance is the opposition offered by the electrons to the flow of electrons in a conductor.
When conductor is connected with battery, the potential difference is produced. Electron start
flow through conductor opposition is also produced. This opposition is called electrical
resistance.
Formula:
According to Ohm’s law, there is a relation between the current flowing through a conductor
and the potential difference across it. It is given by,
V∝I
V = IR
V is called Voltage and I is the amount of current flowing through the conductor.
SI Unit:
Ohm is the SI unit of resistance.
Ohm law states that the current through a conductor between two points is directly
proportional to the voltage across the two points, and inversely proportional to the resistance
between them. V, I, and R, the parameters of Ohm’s law.
I = V/R
Ohm’s law is among the most fundamental relationships in electrical engineering. I relates the
current, voltage, and resistance for a circuit element so that if we know two of the three
quantities we can determine the third, Thus, if we measure the current flowing in a resistor of
known value, we can deduce the voltage across the resistance according to V = IR, Similarly, if
we measure the voltage across a resistor and the current through it, we calculate the
resistance of the element to be
R = V/R
Breadboard:
Breadboard is a thin board used to hold electronic components (transistors, resistors,
chips, etc.) that are wired together. Used to develop prototype of electronic circuits,
breadboard can be reused for future jobs. They can be used to create one of a kind systems
but rarely become commercial products.
Power:
Power is the amount of energy transferred or converted per unit time.
In the International System of Units, the unit of power is the watt,
equal to one joule per second. In older works, power is sometimes
called activity.[1][2][3].
Power is a scalar quantity.
P=IV
Power
Common symbolsP
SI unitWatt (W)
In SI base unitsKg⋅ m2⋅ s−3
Derivation from Other quantities
P = E/t
P =F·v
P = V·I
P =τ·ω
Multimeter:
It is the device which is used to measure resistance, voltage and current in an electrical circuit.
It is a standard diagnostic tool for technicians in the electrical industries. It has four parts
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Display (to note the readings)
Buttons (to select various functions)
Rotatory switch (to select measurement values i.e. volts, ampere or ohm)
Input jacks (to connect test leads)
The principal to find the resistance with multimeter is very simple. Both the leads are
connected with the resistor and the rotate the knob on the nearest greater value. Then
the reading showing on the display is the resistance of the resistor.
Circuit diagram:
Procedure:
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First of all, a resistor is taken and measured its resistance with help of multimeter
The DC power supply was turned on and selected the suitable value of voltage.
The resistor was put into the bred board horizontally
The multimeter knob was set to the appropriate value to determine the current reading.
 The positive terminal of source was connected with the right side of the resistor and
the negative terminal of the source was connected with the black lead of the
multimeter.
 Then the red lead of the multimeter was connected with left side of the resistor and
noted the reading of the multimeter.
 To calculate the current, the voltage of the source was divided with the resistance.
 Then the power consumed by the resistor was calculated by using three different
formulas.
 The experiment was repeated 3-4 times.
 Then the voltage was fixed and the taken different resistances to calculate the power.
Observations & calculations:
Table 1 (Resistance R is fixed)
Sr.No. Voltage Resistance
Calculated
Current(Ical)
Power
Power
Power
=VxI(obs)
= V2/R
=Iobs2xR
1
5.2
2160
0.0024
0.0124
0.0125
0.0124
2
4.13
2160
0.0019
0.0078
0.008
0.0078
3
3.34
2160
0.0015
0.005
0.005
0.0048
4
2.09
2160
0.00096
0.002
0.002
0.0019
5
3.81
2160
0.0018
0.0068
0.0067
0.0069
Table 2(Voltage V is fixed)
Sr.No. Voltage Resistance
Calculated
Current(Ical)
Power
Power
Power
=V.I
= V2/R
=Iobs2xR
1
2.58
2160
0.0001
0.0026
0.003
0.0022
2
2.58
5020
0.0005
0.00129 0.0013
0.0012
3
2.58
5680
0.00045
0.0011
0.0011
0.012
4
2.58
3260
0.0008
0.002
0.002
0.002
5
2.58
5060
0.0005
0.0012
0.0013
0.0012
Precautions.
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All the connections must be very tight.
Record the current at regular interval of voltage.
Least count of voltmeter and ammeter must be properly calculated
Do not pass a large current through the resistance
While measuring the voltage and current the needle of meters should not move out of
the scale.
 For measuring current connect multimeter in series and connect in parallel for voltage
measurement.
 Make it sure that bredboard is insulated from back side to avoid error in readings.
Conclusion.
In this experiment,we calculate our values for voltage,resistanceand current by calculation and we
verify the result by doing the experiment. Also we know more about how capacitor and resistor work.
As a result, we got small amount of errors in our experiment. Most of our errors coming from
measuring voltage, current and resistance due to other effect like heat, air and balance of the hand.
We provide that resistance is the quotient of voltage and current keeping current constant.