Susan Brown

[Susan Brown]

Yes – circuit is the answer.

If you have voltage and a complete circuit, you will have current (electron flow).

In order for that circuit to do work and not immediately short out, you also need a load. But that’s not what this particular question is asking.

I assume you’d like that quiz to be reset?

[Susan Brown]

Hi Jerrod,

I’ll give you some info here, but also I suggest you rewatch the second video in Unit 4.

Remember that when current flows through a load, there will be a voltage drop (difference in voltage) across that load, and it will also do work.

Either one of those (voltage drop, Ed, and power/work/heat, P) can be calculated if you know the resistance of the load and the current going through it.

In the case of Questions 7 and 8, we’ve got two loads in series, and we want you to find the heat generated by each one (P).

Remember to start these types of calculations with what you know and what you are asked to find. You know the resistance of each load, and you also know the current flowing through the circuit (you found that in Question 6). You are asked to find the heat generated by each load (P).

What formula would you use to find “P” for each load?

[Susan Brown]

Hi Andrew,

Let’s start with talking about what you’ve watched so far in the course.

Were you able to follow and understand the video in the “Thermodynamics and Phase Change” (unit 3)?

Combining that information with what we describe in the video in unit 2 is a pretty strong overview.

Let me know…

[Susan Brown]

Hi Michael,

Thanks for your idea. Most people do not ask for more practice on Ohm’s Law calculations, because they don’t like them! But I’m glad you would like to feel more confident about these.

At this point, I think you’ll be fine if you just master the questions that you’ve already encountered. Are there any that you aren’t sure about? I see that on the Module exam you missed the question about the heat generated by the loose connection. If you aren’t confident on how to do that, we can work on it together here. Let me know.

The Midterm Exam will give you a little more practice on these calculations, as it is designed to be part of the learning process. In other words, don’t stress out about trying to pass it on your first attempt.

[Susan Brown]

Hi Andrew,

It’s all how you round the fractions. I just did the whole series on my calculator without rounding until I got my final number, which was 68.6 ohms.
(1/80 = 0.0125, 1/480 = 0.002)

But when we’re talking about resistance of 67 vs. 69 ohms – those are close enough to be called “the same” 🙂

[Susan Brown]

“So what you’re saying is that knowing how to plug in the correct numbers or calculate the formula correctly is not as important as knowing that equivalent resistance is always less than the smallest resistance?? ( Smaller the or equal to) 9.9 is actually 10 if we’re rounding.”

Basically, yes.

It is interesting to note that the closer together the resistances are, the smaller the Req.

For example, say we have R1 = 10 ohms. Here are the Reqs for a variety of R2s

R2 = 10 ohms, Req = 5 ohms
R2 = 100 ohms, Req = 9 ohms
R2 = 1000 ohms, Req = 9.9 ohms

This makes sense if you think about the current flow through each parallel circuit, and that the total current flow equals the sum of the currents in each parallel circuit.

[Susan Brown]

Hi Elisha, and welcome!

Refrigerators are a big topic – we have a whole Advanced course that goes into more detail on them – so you’ll need to give me a little more specific question for me to help you with.

Are there questions on the quiz that you didn’t understand what the answers should be?

[Susan Brown]

Great question, which allows me to make a couple of important points.

1. *The* most important thing to remember about Equivalent Resistance is the rule of thumb: that the equivalent resistance of loads in parallel will be something *less* than the smallest resistance. Being able to run the calculation and see what the Req is for a variety of combinations of resistances is helpful, but you can also get by with just understanding the rule of thumb.

2. It is fine to round an ohms reading to the nearest whole number. Resistance is usually not a measurement that needs to be more precise than that. The same is true for voltage and power/watts. Generally speaking, current measurements (amps) are the only ones where you need to maintain a decimal place. For example, you would not want to round 3.4 amps down to just 3 amps.

So, you can round 5.74 ohms up to 6 ohms and then your Req equation would be 1/[(1/6) + (1/R2)…]

Does that make sense?

[Susan Brown]

Think of what “upstream” means. If you are on a river, “upstream” means the source of the water (or the opposite direction of the flow). The regulator comes in the gas stream before the appliance, so the appliance is “downstream” of the regulator.

[Susan Brown]

*Above* the diaphragm

• This reply was modified 2 years, 2 months ago by Susan Brown.

[Susan Brown]

Yes, this doesn’t really count as a normal “reset” request.

[Susan Brown]

Hi Dario,
No worries – I reset you so that you can start fresh with two attempts.

As to what may have happened – you probably just had some kind of brief internet connectivity glitch that interrupted the test.

[Susan Brown]

That’s correct!

[Susan Brown]

“Run the washer in a drain cycle and see if you’re getting 120 V AC at points NA2-1 and BL3-1 on the Main PWB”
is correct. That *is* testing the drain pump voltage, using EEPs.

[Susan Brown]

This is very similar to Question 9 on the Midterm exam. Check your email for more detail.

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