Susan Brown

[Susan Brown]

Great! Thanks for using the Forums 🙂

[Susan Brown]

Hi Kenneth,

These loads are in series in one circuit. Will the current change throughout the circuit? (if you think “yes”, then review the first video in Mod. 3, unit 5).

You do need to use the equation E = I x R to calculate each voltage drop, but you have to use the correct value for the current (I) to get the correct answers.

[Susan Brown]

Hi Rees,

Thanks for posting in the Forums!

A great video to rewatch that shows these types of calculations is the last video in Mod. 3, unit 3 on the heat generated by a loose connection. Watch that, and re-create the calculations in your notebook. Then look at the questions in the Unit 8 quiz and see if they make more sense.

If you don’t follow something we’re showing in that video, please let me know and I’m happy to help you further.

[Susan Brown]

No problem! Sam (who is a mister) is one of the folks helping you. One of us will get back to you ASAP.

[Susan Brown]

Hi Samuel – could you please be more specific about which question you’re referring to? Thanks!

[Susan Brown]

Hi Michael,

The fact that the terminal is labelled NO, and it’s in the “normal” state, is what tells you that the switch is open. And that is why you would measure 12vdc.

Does that answer your question?

[Susan Brown]

Hi Ryan,

Thanks for posting in the forums!

One of the keys when looking at schematics is to “see” it from the electron’s point of view. Electrons don’t “see” bends in a wire, for example, like we do when looking at a diagram.

That’s one reason we suggest doing the “Zen trick” on the loads, when you aren’t sure if they are in series or parallel. Try doing that on the light bulb – “become” the light bulb – both with the switch open and then the switch closed. Does that help you figure it out? Let me know!

[Susan Brown]

That’s correct! (I’m going to hide those answers so future students won’t see them.)

[Susan Brown]

Correct!

There’s a lot to learn in the Basic Electricity module, and it can be quite a challenge. Please feel free to ask more questions here as needed – we’re glad to help!

[Susan Brown]

You are essentially correct!

A. Don’t think in terms of “least resistance” – that can lead you astray. Current will take any valid, complete path unless there is a shunt. When it has an option to take a path with (essentially) zero resistance, then all the current will flow through that path instead of alternate paths that have loads (resistance). So, that’s the case here. 100% of the current will flow through the branch with the closed switch instead of the path with the element.

B. Since the switch is open, all current will flow through the branch with the element.

C. Current will flow through both loads, in inverse proportion to the resistance of those loads.

Remember the formula for current? I = E/R

In other words, if R2 is twice as large as R1, then it will have half the current flow that R1 does.

And here’s where saying current follows the path of least resistance is flawed. R1 has the least resistance in the scenario I just proposed, but it does not get all of the current. It just gets more.

Let me know if you have any follow-up questions.

BONUS QUESTION: In Circuit A, if we did not have the light bulb in the circuit, what would this circuit configuration be depicting?

[Susan Brown]

These are good questions, and it’s great to get a handle on this. Here are three scenarios. When the electrons get to the point where there are two possible paths, what will they do? In other words, tell me for each scenario (A, B, and C) how much current will flow through the different branches. For example, will 100% of the current flow through one or the other, or will it divide up in some way?

Are you able to answer this yet, or are you still unsure?

[Susan Brown]

Correct – no current. If there’s no current flowing, even when we have some voltage present, that means there’s an ____ in the circuit (fill in the blank). (it’s good to be more specific than “bad”)

And, the measurements we give you tell you which side the ____ is on.

[Susan Brown]

Voltage Drop:
Look in Unit 8. In the text before you get to the video, we define voltage drop and show you how to calculate it. Do you see it there?

For Equivalent Resistance of parallel loads:
We cover this in the 3rd video of Unit 5, and in the text below that. If you don’t want to do the actual calculation, you can just tell us the rule of thumb, which we show you in that video.

Let me know if you have follow-up questions!

[Susan Brown]

This is a normal household circuit, so 120vac. You’d have L1 on one side of the bulb, and N on the other side. The bulb is good, but no voltage drop. We do measure 120vac wrt N from one side of the bulb.

Is current flowing?

[Susan Brown]

Yes, you are overthinking this! The first choice answer you gave on the exam is correct.

At some point in the course we told you that when you see a component on a schematic, you should categorize it as a switch or a load. Loads do work (and therefore create voltage drop), but switches do not. If you know which category a fuse is in, then this answer is simple.

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