5 figure 6 display list in datastudio now remove the

5

Figure 6: Display List in DataStudio.
• Now remove the Current Probe. Repeat the previous step but with the Current Probe in
series with R
2
and subsequently R
3
so as to measure the current in the other two branches.
At this point you should have recorded 3 current values and 9 voltage values (3 for each
of the circuit components).
• Are the voltage values you measured the same each time? If not by how much are they
off? Any difference may be due to the Current Probe being placed at different points in
the circuit. What is the Current Probe doing to affect the voltage differences?
• Now average the voltages for each component and use these average values to verify
Kirchhoff’s Loop Rule is satisfied. Divide the averaged voltage differences of each resistor
by their resistance value you measured earlier. By Ohm’s Law this should be the current
passing through it. Compare these values to the associated currents you measured ( I
1
,
I
2
, I
3
). Are they reasonably close? Check that these currents satisfy Kirchhoff’s Junction
Rule you wrote down at the beginning of this section.
• Lastly compare the measured currents to those you first calculated from Kirchhoff’s Circuit
Rules. Are they in agreement?
Kirchhoff’s Circuit Rules can be applied to complicated circuits with an arbitrary number of
loops. As more loops are added the current is further divided and the current in the new
branch becomes another unknown. The Circuit Rules (combined with Ohm’s Law) represent a
general relationship between the resistances/voltage differences across circuit components and
the currents flowing through the various branches of the circuit. The circuit rules do not require
the currents to be the unknown values. They can also be solved for an unknown resistance, but
that will require knowing one or more of the current values. The next section will deal with a
multi-loop circuit that is used to measure unknown resistance values.
6 Black Box Analysis
In this section we will use the knowledge developed in this as well as previous labs to analyze
several unknown circuits. These circuits are contained within the “black boxes” provided you.
The boxes contain between 3 and 5 circuit elements connected in an unspecified arrangement.
The contents of the box are as follows:
6

• Box A (3 red plugs): 4 resistors of value - 20, 51, 100, 200kΩ
• Box B (3 black plugs): 4 resistors of value - 20, 39, 51, 82kΩ
Note these boxes have several banana plug sockets which attach at various points on the circuit.
Utilizing all available resources (multimeter, signal generator, Science Workshop/Data Studio,
etc.) you will attempt to determine the structure of the circuits located inside.
• Each black box has several plugs, each connected to a different point on the unknown
circuit. Note the number of connections; label them and make a table of all the pairs of
plugs across which you could measure the DC resistance (i.e. for plugs A, B and C one
would have R
AB
, R
AC
and R
BC
)
• Draw out the equivalent circuit based on the measurements you’ve made. Now considering
what components are known to be in each box, determine and draw the circuit arrangement
containing those components.