EXPERIMENT NO. 3: DC POWER MEASUREMENTS

3.1 EXERCISE TITLE: POWER IN A SERIES RESISTIVE CIRCUIT

OBJECTIVES:

1. To determine the power dissipated in a series resistive circuit by using a power formula.

2. To verify the results with a multimeter.

EQUIPMENTS REQUIRED:

1-F.A.C.E.T Base Unit

1-DC FUNDAMENTALS Circuit Board

2- 15 Vdc Power Supply

1- Multimeter

PROCEDURES:

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 4.1-3. Place the switch in Position A.

3. Calculate and record the values of RT , I T, V R1 and V R2. Now measure and record those same values.

I T = 5 mA, RT = 3 kΩ, V R1 = 5 V, V R2 = 10 V

4. When you consider circuit tolerance, are the calculated values and the

measured values nearly the same or totally different? They are the same.

5. Using the formula P=EI, calculate the total circuit power. PT = 75 mW

6. Using the formula P=E2/R, calculate the power for R1. PR1= 25 mW

7. Using the formula P=I 2R, calculate the power for R2. PR2 = 50 mW

8. Are the values of power calculated in steps 6 and 7 equal to the total circuit

power dissipation you calculated in step 5 (PR1+PR2=PT )? Yes

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? R4 is added, R2 was removed.

10.Calculate and record the values of RT , I T, V R1, and V R4. Now measure and

record those same values.

RT = 2 kΩ, I T = 7.5 mA, V R1= 7.5 V, V R4 = 7.5 V

11.When you consider component tolerances, are the calculated values and the

measured values totally different or nearly the same? They are nearly the same.

12. Calculate the power values of PR1, PR4 , and PT.

PR1 = 7.5 mW, PR2 = 7.5 mW, PT= 15 mW

13.The power values recorded in step 15 are higher than the values recorded in

steps 5, 6 and 7. Is the difference due to the circuit in step 12 having a higher

RT and a lower I T than the circuit used previous, or is it due to the circuit in

step 12 having a lower RT and a higher I T?

It is due to the circuit in step 12 having a lower total resistance and higher total current.NOTE: D not turn off the power sources. The F.A.C.E.T setup will be used for

a review question.

CONCLUSION: - We therefore conclude that in order to determine the power dissipated in a

series resistive circuits we should use the power formula such as P=IE ;

I=E/R ; E2/R.

- In order for us to verify the result we have computed we should compared

the computed value to the data we get in the multi meter.

- We have concluded that the total circuit power in the series circuit is equal

to the summation of the power dissipated by resistor.

3.2. EXERCISE TITLE: POWER IN A PARALLEL RESISTIVE CIRCUIT

OBJECTIVES:

1. To determine the power dissipated in a parallel resistive circuit by using a

power formula

2. 2. To verify the result with a multimeter

EQUIPMENT REQUIRED:

1-F.A.C.E.T Base Unit

1-DC FUNDAMENTAL Circuit Board

2-15 Vdc Power Supply

1-Multimeter

PROCEDURES:

1. Turn off the power sources. Insert the DC FUNADEMENTALS circuit board

into the base unit. Turn on the power sources.

2. Locate the POWER circuit block, and connect the circuit shown in Figure 4.2-

5. Place the switch that is in the POWER circuit block in Position A.

3. Based on the resistor color code, determine and record the values of R2 and

R3. R2= 20x102 Ω, R3 = 20x102 Ω

4. Measure and record the voltage drop of R2 . What is the power dissipated by

R2 (Use PR2 = V R22/R2)? V R2 = 5.2 V, PR2 = 13.52 mW

5. Measure and record the current through R3. What is the power dissipated by

R3 (Use PR3 = IR32x R3)? IR3=¿7.51 mA, PR3= 112.8 mW

6. What is the total power dissipated by the parallel branch of this circuit?

PT = 126.32mW

7. Use the product-over-sum method to calculate and record the equivalent

resistance of R2 and R3. R23= 1 kΩ

8. Move the switch from position A to position B. Measure and record the

voltage across R4. V R4 = 7.47 V

9. Based on the value recorded of step 8 calculate the value of resistance need

to dissipate 56.250 mW of power (Use R=E2/P) R= 991.02 Ω

10.Use the resistive color code to determine the value of R4. Does this value

match the value you calculated in step 9? R4 = 10x102 Ω

11.Measure and record the voltage across R4. Use the value to calculate and

record the current and power through R4. V R4= 7.47V, IR 4= 7.47mA, PR4= 55.8mW.

12.Based on your observations can the parallel circuit be duplicated by an

equivalent resistance? Yes.13. If the voltage source in Figure 4.2-5 were doubled to 30Vdc, what would

happen to power dissipation across R4 (Use the square law relationship of

power to voltage)? PR4= 0.22 W

14.Calculate power across R4 when V A, the source voltage, is 30Vdc. Does your

answer agree with the answer given in step 13? PR4= 0.22 W, Yes

15.Do not turn off the power sources. The F.A.C.E.T setup will be used for a

review question.

CONCLUSION

- We therefore conclude that in order to determine the power dissipated in a

parallel resistive circuits we should use the power formula ( P=IE )

- We conclude that in order for us to get the true value , the calculated data

should be or at least almost the same to the value we get in the multi

meter.

- We have concluded that the total dissipated power in the parallel circuit is

equal to the summation of the power dissipated by resistor in the parallel

branch.

3.3. EXERCISE TITLE: POWER IN A SERIES- PARALLEL RESISTIVE CIRCUIT

OBJECTIVES:

1. To determine the power dissipated in a series-parallel resistive circuit by

using a power formula.

2. To verify the results with a multimeter.

EQUIPMENT NEEDED:

1-F.A.C.E.T Base Unit

1-DC FUNDAMENTALS Circuit Board

2-15 Vdc Power Supply

1-Multimeter

PROCEDURES:

1. Turn off the power sources. Insert the DC FUNDAMENTALS circuit board into

the base unit. Turn on the power source

2. Locate the POWER circuit block, and connect the circuit shown in Figure 4.3-

3. Place the switch in position A.

3. Measure and record the following circuit values

V A = 14.92 Vdc R1 = 994 Ω

V E = 5.23 Vdc R2 = 1941 Ω

V R1 = 9.69 Vdc R3 = 1953 Ω

I T = 7.51 mA RT = 1967 Ω

4. Calculate and record the values of I R1, IR2, and I R3.

IR1 = 7.59 mA, IR2 = 3.79 mA, IR3 = 3.79 mA

5. Calculate and record the values of PR1, PR2, and PR3.

PT = 113.32 mW, PR1 = 57.26mW, PR2 = 27.9mW, PR3=28.13 mW

6. Place CM switch 16 in the ON position. Record the following values

NOTE: To measure RE make sure that the R2- R3 circuit is isolated from R1 and

V A.

V A = 14.91 Vdc R2 = 1942 Ω

V E = 3.86 Vdc R3 = 1954 Ω

V R1 = 11.04 Vdc RE = 1988.99 Ω (calculated, CM 16 not included)

I T = 9.93 mA RE = 1485 Ω (measured)

R1 = 994 Ω

7. CM switch 16 added a 1,000Ω resistor to the circuit. Was this resistor placed

in parallel or in series with R2 and R3? This additional resistor cause RE to

equal what values? It is connected in parallel withR2 and R3.RE = 1485 Ω

8. Calculate and record the values of I R1, IR2, IR3 and IRCM.

IR1 = _______A IR2= _______ A

I R3 = ______ A I RCM = _______ A

9. Calculate and record the values of PR1,PR2,PR3,PRCM and PT

PR1 = _________W, PR2 = ___________ A

PR3= __________W, PRCM =____________A

PT =329.68W

10. CM switch 16 added a 1000Ω resistor in parallel with R2 and R3, which

lowered RE to 500Ω. Did this cause I T to increase or to decrease? Did the

change in I T cause total circuit power to increase or to decrease? To what value?

Increased, I T = 9.93 A

11. Turn off CM switch 16. To complete Table 4.3-1, you will evaluate the

transfer of power from the source to the load. Resistor R1 will act as the source

resistor (RS) at 1,000Ω. You will vary the load resistance (RL) in three steps,

500Ω, 1,000Ω, and 2,000Ω. You’ll also measure the load current ( I L) between

the source voltage and R1.

I L(500W ) = 29.77 mA

I L(1000W ) = 7.5 mA

I L(2kW ) = 7.42 mA

12. Verify that the switch is in position A. Using 2 two-post connectors, connect

R2 and R3 as R1. Place CM switch 16 in the ON position. With R2, R3 and RCM in

parallel, measure and record the value of RL. Figure 4.3-4 shows the circuit

configuration and its equivalent with respect to R s and RL.

13. Measure and record the value of resistance where RL is 500Ω

RL

ohms

I L

mAdc

V L

Vdc

PL

mW

500 29.77 14.89 443.13

1,000 7.5 7.5 56.25

2,000 7.42 14.84 110.11

14. Place CM switch 16 in the OFF position. With R2 and R3 in parallel, measure

and record RL.

RL = 973 Ω

15. Measure and record the values of Table 4.3-1 where RL is 1,000Ω

16. Remove R3 from the circuit. Measure and record RL. RL = 3000 Ω

17. Measure and record the values of Table 4.3-1 where RL is 2,000Ω. RL =

______Ω

18. Refer to Table 4.3-1. At what R value did the voltage source transfer

maximum power? Was maximum power transferred at this value because RL

was less than R s, equal to R s, or greater than R s? _____________

19. When RL was 500Ω and 2,000Ω was more power transferred or was less

power transferred? Was load current maximum when load resistance was

maximum or minimum? It has more power when RL is 500 Ω and less when 2000Ω. The load current is at its maximum when the load resistance is in its minimum.

20. When was the load voltage maximum- when load resistance was maximum

or when load resistance was minimum? ___________

21. Do not turn off the power sources. The F.A.C.E.T setup will be used for a

review question.

CONCLUSION

- We therefore conclude that in order to determine the power dissipated in a

series-parallel resistive circuits we should use the power formula (E2/R).

- In verifying the result in we had computed we should compare it to the

value that we have measured.

- We also conclude that we can determine the total power of a circuit by

adding the power dissipated in both series and parallel component of the

circuit.