construction of even the most complex electronic equipment. It is also
very important to become familiar with the vocabulary of electronics; many students nd this specialized
jargon unnecessary confusing. Below is a short glossary listing all the important terms you will come across
in this lab.
Terms
Bus(s): long, electrical path to which many side connections may be made. (ex: Power or Ground
Bus, both usually made of a ceramic material)
There are several on your bread board, two running horizontally across the top and several running
vertical on the main part of your board. This is where you will build almost all of your components.
Current: (symbol: I) rate of ow of electric charge past a point. Its unit of measure is the Ampere,
or A, which is dened as: 1 A = 1 Coulomb / 1 s. It should also be noted that, by convention,
current ows from a more positive voltage to a more negative voltage (even though the actual ow
of electrons is in the opposite direction).
Important point: you should remember to always refer to voltages existing between or across two
points in a circuit. Conversely, current is referred to as existing at a point in a wire or device.
Remember:
Voltage between or across two points in a wire.
Current at a point in a wire or device.
Function generator: an instrument used to produce electric signals whose frequency varies with time.
There is one on the left side of your bread board, and it can produce sinusoidal, square and triangle
shape waves. There are also two vertical sliders which are used to change the amplitude and frequency
of the signal produced.
Ground: a reference voltage level which is usually deemed as 0 volt. Ground can be thought of as
the voltage of a metal conducting rod that has been driven into the earth.
Instrument cases are often grounded to the third, often round, pin of a 120 volt power connector. Input impedance: the eective resistance of a circuit used to measure some external voltage.
To clarify, consider the following: in the lab you are using a device to measure the voltage battery,
that is the potential dierence across the batterys terminals. It often overlooked that in the real
world, the mere act of measuring a voltage causes current to be drawn from the source that is being
measured. The meter you are using to measure the voltage is at the same time drawing current out
of the battery. The input impedance of the meter is determined by dividing the measured voltage
reading by the current drawn by the meter during the measurement. The above example deals with
DC or direct current, when the voltage being measured is constant with respect of time. For AC
or alternating current, the ratio of the time rate of change of these two quantities, the derivative
dV /dI, is the measure of input impedance. It should be noted that high input impedance is often
very desirable when designing circuits.
Output impedance: the eective resistance of a circuit used to supply a certain voltage. This is the
ip side of input impedance.
Once again we will use an example to clarify: in the lab you are using a battery that is labelled 1 volt.
You connect the device you wand powered to the battery ( for instance an electric lamp) while at the
same time measuring the voltage across its two terminals. As you draw more and more current out
of the battery to make your light brighter, you notice that the voltage across the two terminals of the
battery falls below one volt. A frequently neglected fact is that any real battery will supply less than
it is rated to (in our case 1 volt), if we draw from it a lot of current. The supplied voltage divided by
the current drawn denes the output impedance battery. For a case where the source is producing
alternating current, a battery produces DC current, we use the derivative dV /dI to determine the
output impedance. Low output impedance is often very desirable when designing circuits.
Jumper: a small piece of wire or other little connecting device that is used to make an easily change-
able electrical connection between to points of a circuit. You will use them when connecting parts
of circuits together. (They are also commonly found on the back of computer CD-ROMs and hard
drives to allow you to change certain settings quickly.)
Leads: (rhymes w/weeds) wires that usually have various types of connector(s) at their ends.
Passive component: a resistor, capacitor or inductor. Do not require a power source to function.
Active component: a device like a transistor that requires a power supply to function.
Pot or Potentiometer: a special three terminal resistor. Two of the terminals, A and C, are at
the opposite ends of the resistor and have a xed resistance value between them called R
AC
. The
third terminal, the wiper, B, makes contact with the resistor between A and C. Its position can
be mechanically changed causing it slide along the length of the resistor. The resistance relation
R
AC
= R
AB
+ R
BC
holds true as a result. Pots are used to weak circuits because they allow for
changeable resistance and thus adjustable voltages. There are two along the bottom of your bread
board. (Have black knobs to control the wiper)
Power: a constant (or sinusoidally varying) voltage used to provide the energy that runs a circuit.
Distinguished from the signal, which is the electrical behavior a circuit measures.
Resistor color code: resistors have a relatively simple labeling convention which allows one to deter-
mine the resistance it provides in Ohms. Annexe 1 shows you how to do this.
Sag: the result of nite output impedance. As explained above, as current is drawn from a source or
circuit, the voltage it supplies may decrease, or sag, as the current being drawn is increased. Signal: a constant or time varying voltage which is being measured in some particular application.
Lab activities
1. Series circuit
On your bread board, connect 5 volts to ground through ve 100 K resistors connected one after
another in series. Using your AC powered multi-meter (the one plugged into the wall, hence AC
powered) measure the voltage across each resistor and indicate these on a drawing of the circuit. Ask
your instructor what symbols to use to draw the diagrams. Compute the current that should ow in
this circuit using Ohms Law. Compute the voltage drop across each resistor using your calculated
current and resistor values. Compare with the actual measured voltage drops. What did you nd ?
Tricky question: How could you use this circuit to supply 0.3 V if all you had was a 1.5 V battery
and these ve resistors ? (Hint: look up what a voltage divider is)
2. Parallel circuit
On your bread board, connect 5 volts to ground through ve 100 K resistors connected in parallel.
Measure the voltages of signicance with your AC multi-meter and indicate them on a drawing of the
circuit. Compute the current that should ow in this circuit theorically using Ohms Law. Compute
the voltage drop across each resistor using your calculated current and resistor values. Compare with
the actual measured voltage drops. What did you nd ?
3. Meter input impedance
Using the series circuit you constructed in part one and your battery powered multi-meter, measure
the voltage across one of the resistors. Be sure you have the measuring leads plugged into the right
receptacles (ask) and the instrument selector switch on the right range for this measurement. You
should get an answer that is inconsistent with the answer you arrived at in part 1. Why is there an
inconsistency ? (The AC powered meter has an input impedance of 10 M while the DC (battery)
powered meter has an input impedance of only 25 K per volt (25 K times the full scale voltage
reading))
Explain quantitatively(without math) how this causes the dierences in the measurements. Which
reading is right? Repeat with your parallel circuit setup. What do you nd ?
4. Current source
Lets assume that you need a circuit to supply a constant 1 mA current to calibrate some current
measuring device. You could do this by connecting one end of a 15 K resistor to a 15 volt source.
(Right ? Check) The other end of the resistor will supply 1 mA. Lets test to see if this works. To
mock the behavior of our circuit that needs 1 mA, connect a resistor directly to ground (a load
resistor). Start with a 100 K resistor. Does the current source work ? (meaning does it supply 1
mA ?)
Next use a 500 K resistor and check the current again. Use a few more resistors, and in your report,
plot the current supplied as a function of the voltage across the load resistance. (current supplied on
the y-axis, voltage on the x-axis) The compliance of a circuit can be dened as the output voltage for which the supplied voltage
drops by 10%. What is the compliance of our 15 K/15 V current source ? Would the output
impedance of an ideal current source be high or low ?
5. Voltage source
Assume you need a circuit to supply a constant 1 mV voltage. One can do this by constructing a
circuit as follows:
As seen above, the point of junction of the two resistors will sit at 1 mV (this is a 1 to 15,000 voltage
divider). To take the place of the circuit requiring 1mV voltage, construct a load resistor once again,
connected to the voltage divider at the junction. Start with a 1 K resistor. Does the voltage source
work as desired ? Next use a 500 load. Work ? Plot the current supplied as a function of the
current measured at the load resistor. The compliance of the voltage source can be dened as the
output current for which the supplied voltage drops by 10%. What is the compliance of our 15 K/1
mV voltage source ? Would the output impedance of an ideal voltage sou