Susan Brown

[Susan Brown]

Those are correct! Has this information helped you?

[Susan Brown]

Where are you putting the two probes – one in either slot of the outlet?

And are you sure you have the meter set on measuring VAC?

[Susan Brown]

Let’s try this exercise.

Here are two loads in series in an L1-N circuit, with resistances of 100 ohms and 50 ohms.

I’ve labelled 3 testing points: A, B, and C. There is also a separate Neutral point that we can use as a reference.

If you did the following voltage measurements, what do you think you would get?

1. A with respect to C (in other words, one probe on A, the other on C)
2. A wrt B
3. B wrt C
4. A wrt N
5. B wrt N
6. C wrt N

If you don’t know all of them, that’s fine – just answer what you think and we’ll go from there.

[Susan Brown]

Good questions.

First of all, don’t think of voltage as “getting” to loads. Think more of voltage being “present.” Current is movement.

The same current will be measured at every point in the load.

The voltage you measure will depend on what your reference point is. It’s always “with respect to” (“wrt”) something.

If you put your probes on either side of a load, you’ll measure the voltage drop across that load (Ed = I x R).

I’m going to create a diagram that shows this better later today and will post it, to help you out.

[Susan Brown]

A series circuit is just describing a circuit with one or more loads in it, where they are connected one after another.

The relationship between voltage (E), current (I), and resistance (R) in a series circuit is E = I x R. This tells you how changing one value will affect the others.

In the real world, in a typical circuit, the source voltage will be set – either 120 or 240.

Then the circuit current will be determined by the total resistance in the circuit.

I = E/R

So, if R is increased, I will decrease. That is true regardless of what the source voltage is.

(In Unit 8, you’ll learn that you can calculate the “voltage drop” across each load using E = I x R, which is another way to use that same equation.)

[Susan Brown]

1. Your example is correct IF the two loads have the same resistance. If they don’t, then the voltage drops will be different (proportional to the resistance… E = I x R).

Go back and look at the Midterm Exam in Core, Questions 2, 3, and 4 where you had to calculate a scenario with 3 loads in series with different resistances.

2. Current is electrons hopping from one atom to the next. They are like tightly packed billiard balls in a track – they are either all moving at the same rate, or not at all. So, in a circuit, the electrons are moving at the same rate throughout the wire, regardless of where they are (on the line side or the neutral side).

The difference between the two sides of the circuit is the voltage. The neutral end is always at ground potential. The line (or, “hot”) end is rapidly shifting from +120vac and -120vac, creating the charge that causes electrons to move back and forth towards the more positive side of the circuit.

This motion of the electrons through a load creates a voltage difference (“drop”) from one side of the load to the other. The sum of the voltage drops across the loads that are in series will total the source voltage.

Does this help?

[Susan Brown]

Depends on the model, but yes, they can. Will still be separate tubes.

[Susan Brown]

They are completely separate sealed systems. The tubes may run side-by-side at certain points (e.g., the condenser), but the refrigerant never mingles.

[Susan Brown]

Okay, I tried adding some more space.

If that doesn’t work, you might have to try a different browser.

Does the last video show up bigger than the others in that unit?

[Susan Brown]

That’s interesting – it’s the first time we’ve heard of this happening. What are you watching it on?

I tried adding a couple of blank lines after the video… try again and see if it has changed.

[Susan Brown]

Hi Thomas,

I also saw your followup post that you read over the info about the Midterm.

Approach the Midterm as part of the learning experience. The open-answer format and a few of the questions we ask will challenge you to apply the basic electricity concepts that we’ve been teaching. It’s very common to need more than one attempt to pass this one, but it helps things to “click” for lots of students.

There are only 9 questions, but some of them may take some time to think about.

[Susan Brown]

Hi Andrew – did you click the button to mark the unit as complete?

[Susan Brown]

I love seeing a student paying attention to details! 😀

We want students to be comfortable with either letter. We say in the lesson:

Voltage is measured in units called Volts and is represented by the letter V or sometimes you’ll see the letter E used.

Keep up the good work!

[Susan Brown]

Hi Darren,

The video played fine for me. More than likely if you closed/reopened your browser, and/or cleared your cache, it would play normally. But you aren’t missing much – he’s just talking about the valve near the bellows that can cause water to back up. You can basically read the text on the photo and understand the point.

[Susan Brown]

Yep! And I see you found an older topic on this same question 🙂

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