Lab 7

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Updated: 2/2/2013

__Guiding Question:__

- What is the inductance, L, and the resistance, r, for the inductor between 13 and 14 in YOUR "thin" box, the inductor you will need to use in Lab 7?

**IMPORTANT:**

You __must__ bring an extra copy of the cover page for your Lab 6 report
so you can use the abstract from that report while doing Lab 7. That abstract
will need to specify which "thin" box you used and the values of L and r that
you measured because you will need that information to do anything in Lab 7.

__Preparing for the lab:__

We will be doing "Lab 36" with the addition of an extra step where we use the oscilloscope to measure the phase angle between current and voltage from what we see on the screen.

Answer the pre-lab questions on LON-CAPA after reading the background information on pages 359 through 362 in the lab manual.

__Comments__

Be sure to record the letter that identifies which "thin" box you used, both on your data sheet and in your report abstract. You need it in the abstract so it is available when you do the next lab.

**REMEMBER:**

Your abstract for this lab __must__ identify which "thin" box
contained the inductor you used __and__ specify the values (and
standard deviations) of L and r you determined in this lab. You
will have to use this information in the next lab to (1) find the
correct box to use and (2) supply the value of L and r needed in
the calculations and analysis for that next lab.

**Details:**

Note that the inductor is between the 13-14 connectors for the
"thin" box, while the resistors we will use are all in the
"thick" box. Also note that we will use a different set of
resistors than specified in the manual; we will use ones that
are approximately 330 ohm (7-8), 470 ohm (5-6), 680 ohm (3-4),
and 995 ohm (1-2). **The actual values of the resistors in your
box are written on a label on the "thick" box.** Be sure to
record the actual values in your data table as well as the
identity of the box you used at your lab station. You will
want to be sure that you are using the same lab station for
the next lab.

You can use the sample standard deviation (sigma_{N-1}) rather than alpha in your data analysis. If you do, just change the column heading from alpha to sigma.

**Information covered in lecture:**

We will be doing this lab at the same time we are covering these topics
in class. Specifically, we will sometimes introduce the complex-valued
impedance early in the week and work examples relevant to both this lab
and the next one about the time that you do this lab. You will not find
this material in our textbook or the lab manual, but the complex value of
the impedance Z = R + iX is the reason we plot the corresponding
voltages (found from deltaV = I*Z) on perpendicular axes.
I will give a short introduction to some differences between DC
and AC circuit responses at the start of lab and remind you that
part 1 of this lab is basically a repeat of the demos on phases
that are done in lecture.

__Apparatus__

There are lots of cables for this experiment and the next one.
I suggest using the longest ones (100 cm) as measurement leads
connected to the multimeter (set for AC volts), the next longest
ones (65 cm) to connect the wave generator to the circuit, and
the shorter ones to finish the circuit. If you place the boxes
carefully, you will find that the shortest cables (25 cm) are
perfect for jumpering between them.

Photo of the equipment as you will find it at the start of the lab.

You should recognize the wave generator and frequency counter from the last lab. The "thick" box containing resistors was used for the Kirchhoff lab, while the "thin" box containing the inductor (and capacitors and other assorted items) was used for the RC lab. There is also a compass and protractor for use in doing a graphical solution of the law of cosines, which will also show the change in phase angle as the resistance increases.

The generator will be wired up this week much as it was last week,
but you should pay attention to these details because it will not
be connected for you next week. There is also a very important
detail that you must fix before doing the experiment: the button
indicated by the blue arrow in this picture.

Arrow showing the button for the "sine" function selector.

Our last measurement in the previous lab used a triangle wave at 1000 Hz. You will usually find that the generator is still set for that, as this one is. Be sure to push in the button on the far right to select the sine function for this week's lab, and monitor this next week as well.

__Procedure Changes__

This lab has had a significant addition to it made at the suggestion of a student a few years ago. As described in a handout, we will start by using the oscilloscope to measure the phase angle between the current in the circuit (as determined from the voltage on the resistor R) and the voltage produced by the generator. We will then do the experiment described in the lab manual, where we will use rms voltages to calculate that angle in two different ways.

Other details are given on a separate page.

__Cables__

The set of cables shown in the picture below contains the ones you
will have available for this lab. The set above
the meter stick includes a red-black pair of 100 cm leads and
a red-black pair of 65 cm leads. One of these pairs is usually
used to make connections to the multimeter while the other is
used to connect to the power supply.

The set below the meter stick includes a red-black pair of 40 cm leads, an extra 40 cm lead that is black with red connectors, and a red-black pair of 20 cm leads. The shortest cables are used for connections between nearby points on a resistor box.

__Old Setup__

Photo of the equipment when we did not use the oscilloscope.

Contact me if you have any questions.