ELECTRICAL ENGINEERING DEPARTMENT

ACTIVITY3: DC POWER MEASUREMENTS

3.1 POWER IN A SERIES RESISTIVE CIRCUIT

3.1.1 Program Outcomes (POs) Addressed by the Activity

b. ability to design and conduct experiments, as well as to analyze and interpret data
d. ability to function on multidisciplinary teams
e. ability to identify, formulate, and solve engineering problems
g. ability to communicate effectively

3.1.2 Activity’s Intended Learning Outcomes (AILOs)

At the end of this activity, the student shall be able to:
a. calculate the power in a series resistive circuit using P = EI
E2
b. calculate the power in a series resistive circuit using P =
R
c. calculate the power in a series resistive circuit using P = I 2R
d. compare computed and measured data

3.1.3 Objectives of the Activity

The objectives of this activityareto:
1. determine the power dissipated in a series resistive circuit by using a power formula.
2. verify the results with a multimeter.

3.1.4 Principle of the Activity

The total power (PT) in series circuit is the sum of the power dissipated by each resistor in the
circuit. If the circuit has only one resistor then total circuit power is dissipated by that resistor.
When a circuit has two resistors, each resistor dissipated power, and the total circuit power is the
sum of the power dissipated by each resistor.

The power being used in the simple circuit shown in Figure 3.1-1 is dissipated by R1.
This circuit has a voltage source of 20 Vdc, which causes current to flow through resistor R 1.
Because power is found by the formula P = El, you should determine the circuit current so that
you may find the power.

ACTIVITY 3: DC POWER MEASUREMENTS

 Figure 3.1-1. Power in a simple circuit.

Current through R1 is found by the formula I = E/R.

I = E/R

I = 20V/500Ω

I = 40mA

Once you know the current and the voltage, you can find the power.

P = El

P = 20 V x 0.040A

P = 800 mW

You do not always have to find the total circuit current in order to determine the power
dissipated. The circuit power can be found simply from the formula P = E2/R.

P = E2/R

P = 202/500

P = 400/500

P = 800 mW

When a circuit has more than one resistor in series, you can use several methods to find
the power dissipated by the circuit by the circuit resistors. In Figure 3.1-2, R2 has been added to
the circuit shown in Figure 3.1-1.

ACTIVITY 3: DC POWER MEASUREMENTS

 Figure 3.1-2. Power in a series resistive circuit.

To find the power used in this series circuit, first find the total resistance and the total
current. Then you can determine the total power dissipated by the resistive load and the power
dissipated by each resistor.

RT = R1 + R2 IT = E/R

RT = (500 + 1,000) Ω IT = 20V/1,500Ω

RT = 1,500 Ω IT = 13.30 mA

PT = EI

PT = 20V x 0.0133 A

PT = 266 mW

The total power can be found from the formula below.

PT = E2/(R1 + R2)

PT = 202/(500 + 1,000)

PT = 400/1,500

PT = 266mW

You can determine the power used by each resistor with the formula P = I2R.

PR1 = I2R1 PR2 = I2R2

PR1 = 0.01332 x 500 PR2 = 0.01332 x 1,000

PR1 = 0.000177 x 500 PR2 = 0.000177 x 1,000

PR1 = 89mW PR2 = 177mW

ACTIVITY 3: DC POWER MEASUREMENTS

You may want to check your calculations to see if PR1 + PR2 equals the total circuit power.

P = (0.089 + 0.177)W

P = 266mW

You can now find power in series circuit by using one of three formulas: P = El, P = E 2/R, or P =
I2R. Notice that power is related to resistance by the square function (E2/R or I2R), meaning that
when the current or voltage is halved, the power decreases to ¼ of its previous value.

3.1.5 Materials/Equipment
1- F.A.C.E.T Base Unit
1- DC FUNDAMENTAL Circuit Board
2- 15Vdc Power Supply
1- Multimeter

3.1.6 Procedure/s

1. Turn off the power sources. Insert the DC FUNDAMENTALS circuit board into the base
unit. Turn on the power sources.
2. Locate the POWER circuit block, and connect the circuit shown in Figure 3.1-3. Place
the switch in position A.

Figure 3.1-3. Power in a series circuit.

3. Calculate and record the values of RT, IT, VR1, and VR2. Now measure and record those
same values.

4. When you consider circuit tolerance, are the calculated values and the measured values
Yes
nearly the same or totally difference?_________________________________________

ACTIVITY 3: DC POWER MEASUREMENTS

 75 mW
5. Using the formula P = El, calculate the total circuit power. ________________________

25 mW
6. Using the formula P = E2/R, calculate the power for R1. ___________________________

50 mW
7. Using the formula P = I2R, calculate the power for R1. ____________________________

8. Are the values of power calculated in step 6 and 7 equal to the total circuit power
No
dissipation you calculated in step 5 (PR1 + PR2 = PT)? ____________________________

9. Place the power switch in position B. Which resistor was removed from the circuit?
Which resistor was added and was it added in series with or parallel to the remaining
resistor?
R2 was removed.
________________________________________________________________________

10. Calculate and record the values of RT, IT, VR1, and VR4. Now measure and record those
RT = 2000 Ohms, IT = 7.60 mA, VR1 = 7.59 V, VR2 = 7.54V.
same values. _____________________________________________________________

11. When you consider component tolerances, are calculated values and the measured values
totally different or nearly the same?
Nearly the same
___________________________________________

12. Calculate the power values of PR1, PR4, and P T.

PR1 = 56.25 mW, PR4 = 56.25 mW, PT
___________________________________ = 112.5 mW

13. The power values recorded in step 12 are higher than the values recorded in step 5, 6, and
7. Is the difference due to the circuit in step 12 having a higher RT and a lower IT than the
circuit used previous, or is it due to the circuit in step 12 having a lower RT and a higher
Due to lower RT and higher RT
IT? _____________________________________________________________________

ACTIVITY 3: DC POWER MEASUREMENTS

 3.1.7 Activity Report

Section: 1A Date Performed:

28/05/2022
Course Code: Date Submitted: 28/05/2022
CIRCUITS 1 LAB
Course Title:
CIRCUITS 1
Instructor: Melodia Pahati
Group No.: Activity No.: 3.1
Group Members: Signature:
1.
Jeldin I. Laspiñas
2.
3.
4.
5.

3.1.7.1 Calculations
3.) 5.) 10.) 12.)
RT = R1 + R2 P = EI RT = R1 + R4 PR1 = V x I
RT = 1000 + 2000 P = 15 V x 5 mA RT = 1000 Ohms + 1000 Ohms PR1 = 7.5V x 7.5mA
RT = 3000 Ohms P = 75 mW RT = 2000 Ohms PR1 = 56.25 mW
IT = V / RT 6.) IT = VT / RT PR4 =V x I
IT = 15V / 3000 Ohms P = E2 / R IT = 15V / 2000 Ohms PR4 = 7.5V x 7.5mA
IT = 5 mA P = (5V)2 / 1000 IT = 7.5 mA PR4 = 56.25 mW
P = 25 mW
VR1 = I x R1 VR1 = I x R1 PT = PR1 + PR4
VR1 = 5mA x 1000 Ohms 7.) VR1 = 7.5 mA x 1000 Ohms PT = 56.25mW + 56.25mW
VR1 = 5 V P = I2 x R VR1 = 7.5 V PT = 112.5 mW
P = (5mA)2 x 2000
VR2 = I x R2 P= 50 mW VR2 = I x R4
VR2 = 5mA x 2000 Ohms VR2 = 7.5 mA x 1000 Ohms
VR2 = 10 V 8.) VR2 = 7.5 V
PT = 25mW + 50mW
PT = 75 mW

ACTIVITY 3: DC POWER MEASUREMENTS

3.1.7.2 Conclusion/s: Write at least three (3) conclusions.

* In this experiment we can add the resistors, if the resistors is in series therefore we can easily add the
resistors to get the RT (Total Resistane). Using the formula RT = R1 + R2
* The IT or Current Total can be calculated using the formula IT = V/RT to know the amount of current
that travells along the circuit.
* Every resistor has it voltage value, we know that the total voltage of a dc circuit can be can be divide
according to the number of resistors. We can get the Voltage of a resistor by using the formula V = RI
* The total power produced by R1 and R2 is higher than the total power produced by R1 and R4.
* Adding more resistors in series can reduce the power output of a dc circuit.

ACTIVITY 3: DC POWER MEASUREMENTS

3.1.7.3 Rating(See Attached Rubric)

ACTIVITY 3: DC POWER MEASUREMENTS