ECE LAB report

California State University Fresno

ECE 1

ELECTRIC CIRCUITS BASICS (Part 1)

Before coming to class, please watch the following short videos:

Current, Voltage and Ohm’s Law: https://youtu.be/ssHx81wDYXk

Power and Kirchhoff Laws: http://youtu.be/vEmTjgEAUc4

Summary from the introductory videos:

Ohm’s Law: !

Power: !

Kirchhoff Current Law (KCL): (Algebraic sum of currents at a node equals zero)

Kirchhoff Voltage Law (KVL): (Algebraic sum of voltages around a loop is zero)

1. Using the lab tools for DC circuits: The Instructor will show students the following:

a. How to use the DC power source.

b. How to use the breadboard to build a circuit.

c. How to use the multimeter

V = R . I

P = V . I

2. Lab exercise 1: Ohm’s Law

a. Build a simple circuit using a random resistor supplied by the instructor and a DC power supply (See figure 1).

!

Fig 1. Simple resistive circuit.

b. Vary the voltage and measure the current for each voltage value. Do 5 measurements. Fill the following table:

c. Calculate the average value in the column on the right (V/I). This is your resistance value.

Rcalculated ___________

V (Voltage in volts) I (current in Amps) ! V R

=

d. Using the multimeter, measure the same resistance directly using the resistance measurement feature:

Rmeasured _____________

e. Show your work to the instructor.

f. What is the power supplied by the voltage source?

! _________________________________________

g. What is the power absorbed by the resistor?

! _________________________________________

Observations: On your notebook record all results, and write whatever observation you make from your experiment, and your conclusions.

Lab exercise 2: Voltage division

Resistors in series: If 2 or more resistors are in series, their overall equivalent resistance is equal to the sum of all resistances. Req= R1+R2+…+Rn

Consider the circuit below:

=

Psupplied =

        Presistor =

Fig. 2: The resistors R1 and R2 are in series, and therefore: R(equivalent) = R1 + R2

Using Ohm’s law I can write:

V=(R1+R2).I

Which gives the current expression: !

Now if I want to express V1, the voltage across R1, I can write Ohm’s law for the resistor R1:

!

Replacing I with its expression (above), we get: ! ( !

Or ! ( ! )

V1 is a fraction of V. We call this: Voltage division. And the same formula applies for

R2: ! ( ! )

a. Build the circuit shown in figure 2, using voltage power supply (V) and two resistors of your choice (R1 and R2).

I = V

R1 + R2

V1 = R1I

V1 = R1 V

R1 + R2 )

V1 = V R1

R1 + R2

V2 = V R2

R1 + R2

b. Vary the voltage and measure the voltage V1 and V2 for each value of V. Do 5 measurements. Fill the following table:

c. What does V1+V2 represent?

d. Calculate the average value in the column of V1.

V1(avg) ! ___________

e. Using the multimeter, measure the resistance R1and R2 directly using the resistance measurement feature:

R1measured _____________, R2measured _____________,

f. Choose one row in the table above, and use the value of V and the voltage division formula to calculate the corresponding V1 and V2.

g. Compare to the measured V1 and V2 for that voltage V.

V (Voltage in volts) V1 (v) V2 (v) V1+V2

=

= =

h. Observations: On your notebook record all results, and write whatever observation you make from your experiment, and your conclusions.

Dr. Zoulikha Mouffak ECE Dept. CSU Fresno.