Susan Brown

[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.

[Susan Brown]

To me, they look like series circuits.

Correct. If the switch is open, current will flow through both the heater and the bulb, which are in series along a single circuit.

Why wouldn’t the heater operated when switch is closed?

In order for a load to do work, it must have power (voltage AND current). If the switch is closed, will the heater receive any current? If you aren’t sure, review the basic definition of a shunt (unit 1, unit 5).

can you also clarify why there is a shunt with a switch in this circuit. What role does it play?

The point of the questions at this point in the course is to teach basic electricity and circuits. It’s not a representation of an exact circuit that you might see in an appliance yet. But we discuss briefly how shunts might be used in circuits in the first video in Unit 5.

Does it have to do with resistance of the heater and a switch?

Yes – does a closed switch have any resistance?

I have not seen similar circuit in the book to get clear understanding. On the other hand the explanation of Shunts and Short in the on line presentation made more sense.

You don’t need to find exact replicas of circuits in the material to understand how they work, you just need to apply the basic concepts that you are learning.

I suggest you rewatch the videos in unit 5, and review the definitions in Unit 1. And, continue to answer/ask questions here!

[Susan Brown]

The fact that a closed switch acts like a wire was discussed previously, for example in the first unit 4 video.

Then in unit 5 we teach the “Zen trick” to determine if loads are in parallel with each other or in series. Try that with both of the circuit drawings, A and B, and let me know what you find.

[Susan Brown]

Hi Jay,

I’m not quite sure what you mean by a “shunt with control.” Do you mean the switch that is either open or closed? A closed switch acts like a wire, so with it closed, you have a shunt.

That’s how many circuits are designed – switches open or close to direct which loads are receiving current.

[Author]

Posts