AC Electric Circuits

Performance-Based Assessments for AC Circuit Competencies

51 questions By Tony R. Kuphaldt

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Question 1 of 51

(Template)

Reveal answer

Here, you would indicate where or how to obtain answers for the requested parameters, but not actually give the figures. My stock answer here is “use circuit simulation software” (Spice, Multisim, etc.).

Notes:
Any relevant notes for the assessment activity go here.
Question 2 of 51

Note: when testing the frequency response of the tone control circuit, you may need to replace the headphones with a non-inductive resistor of equivalent impedance, and measure V_out across it.

Reveal answer

Use circuit simulation software to verify your predicted and measured parameter values.

Notes:
A good source of audio signal is the headphone output jack of almost any radio, media player, or other portable audio device. Students like being able to do a lab exercise that directly relates to technology they’re already familiar with.

The higher-impedance the headphones are, the better this circuit works, since the combination of potentiometers and mixing resistors tends to result in a relatively high output impedance. I have used cheap headphones (32 ohm) with some success, given the following component values:

C₁ = 0.1 μF

L₁ = 200 mH (actually two 100 mH inductors in series)

R₁ = R₂ = 1 kΩ

R_pot1 = R_pot2 = 10 kΩ

Some students with limited hearing range have difficulty detecting the changes in tone using 10 kΩ potentiometers. You may wish to use 100 kΩ potentiometers instead for added attenuation. Operating such a circuit is akin to operating a water faucet with “hot” and “cold” water valves: the two settings together determine temperature and flow (tone and volume, respectively, for the metaphorically challenged).

An extension of this exercise is to incorporate troubleshooting questions. Whether using this exercise as a performance assessment or simply as a concept-building lab, you might want to follow up your students’ results by asking them to predict the consequences of certain circuit faults.

If you plan to use this exercise as a troubleshooting assessment, I recommend against inducing the following component failures, as they are difficult to detect when the signal source is music rather than a constant tone of known frequency and amplitude:

Shorted capacitor (C₁)

Shorted inductor (L₁)

Shorted fixed-value resistors (R₁ or R₂)
Question 3 of 51

Note: when testing the frequency response of the tone control circuit, you may need to replace the transformer/speaker assembly with a non-inductive resistor of equivalent impedance, and measure V_out across it.

Reveal answer

Use circuit simulation software to verify your predicted and measured parameter values.

Notes:
A good source of audio signal is the headphone output jack of almost any radio, media player, or other portable audio device. Students like being able to do a lab exercise that directly relates to technology they’re already familiar with.

I have experienced good success with the following component values:

C₁ = 0.1 μF

L₁ = 200 mH (actually two 100 mH inductors in series)

R₁ = R₂ = 1 kΩ

T₁ = 1000:8 ohm audio output transformer

R_pot = R_pot2 = 10 kΩ

Speaker = small 8 Ω unit (salvaged from an old clock radio or other inexpensive audio device)

An extension of this exercise is to incorporate troubleshooting questions. Whether using this exercise as a performance assessment or simply as a concept-building lab, you might want to follow up your students’ results by asking them to predict the consequences of certain circuit faults.