IMPORTANT: this page is only for students who have already taken the Midterm at least once. DO NOT share it with other students or techs. You wouldn't want to spoil their fun, would you? 😉 Thank you!
The Midterm Exam in the Core course is a challenge! More often than not, students do not achieve 90% on their first attempt. But the effort is important at this point. We deliberately are challenging you now so you'll be more competent with Basic Electricity and Circuits, thus better at troubleshooting.
Below is the most common advice we need to give students for all of the questions. Read the ones for the questions you missed, and review the course material we recommend. If you still don't feel confident, then please start a topic in the Ask the Teacher Forums where we are very happy to assist you further. (Click here for a short video on how to use the forums.)
Understanding the behavior of voltage and current in basic circuits is critical! See Unit 4.
Questions 2, 3, and 4
These are all on the same circuit, and each question uses the answer to the previous one as part of the calculation. These are pretty simple Ohm's law calculations, assuming you have a good feel for the behavior of current and voltage in a series circuit. Review Unit 4.
These loads are not in series, they are in parallel. Review the information in Unit 5 about equivalent resistance of parallel loads. We especially want to make sure you know the rule of thumb!
Also, see this topic in the Ask the Teacher Forums.
Re-watch the video at the end of Unit 4 for a similar (but not identical) scenario. Also, pay close attention to the paragraph underneath the video.
Make sure you understand the scenario. These parallel circuits are functioning normally, then the top one (element) fails open. We want to know the change in current or voltage drop in the two circuits and then the effect on the overall current from L1. Review Unit 5.
This is the trickiest question for most techs, but it's a great exercise in looking at a slightly oddly-drawn diagram and determining how the circuits/loads are actually laid out. The key is determining if the loads are in parallel, series, or shunted, and then using what you know about voltage in the different types of circuits to determine voltage drop. (You don't actually have to know anything about gas dryers to answer this - it's just using what you've learned about circuits so far.)
If current were flowing through all of the loads in the diagram, then the main coil would be in series with the booster AND the ignitor, which are in parallel with each other. So, you'd have a series-parallel circuit scenario, which would make for a more complicated calculation to determine voltage drops, like we show in the second video of Unit 5 (and you'd have to know each load's resistance).
However, with the circuits configured as drawn, we are saying that you can determine the voltage drop across each load with the information that's given in the problem statement.
Can you see what's going on with the circuits that allows this? Pay close attention to the detector switch being closed. IMPORTANT: try the “Zen trick” on the booster or ignitor.
NOTE: if you find yourself making assumptions about the resistance of the loads (that they are equal to each other, for example), then there is still something you are missing about the scenario.
First of all, remember that this is an exam covering "Basic Electricity." We want you to practice the basic electrical and circuit info that you've learned. So, think in terms of current, voltage, voltage drop, open and closed circuits for this scenario.
The problem states that the element tests good (has continuity), yet it isn’t heating, even though there’s some voltage present. We do two sets of measurements to get information on what the failure might be. Knowing that the element is good, we can make a general conclusion about the failure in the circuit based on Figure 1. The measurements in Figure 2 are with L1 deliberately disconnected and give us more info on the failure. Re-watch the video at the end of Unit 6 for a similar, but not identical, scenario. Also think about what the zero voltage drop measurement across a known-good load tells us about current flow in this circuit.
Note: the measurements in Figure 1 do NOT indicate that there is a "bad" (open) heating element. If the element was open, you would measure voltage potential across it.