Susan Brown

[Susan Brown]

Right, which of course wouldn’t be that big of a deal with other types of appliances, but no one wants to risk their food spoiling just because of a nuisance trip.

[Susan Brown]

We describe this in the first video during the section on PTC start device failure (starts at about 21 minutes, 25 seconds into the video)

[Susan Brown]

You are correct! Good job!

[Susan Brown]

Hi John!

Yep, this is just a matter of getting the terminology straight.

We should always refer to parallel circuits, plural. Each branch is a circuit with one or more loads. If loads are in parallel with each other, they are technically in different circuits, even if they are tied together at some point.

Does that make sense? You can tell if loads are in series or parallel with each other by doing the Zen Trick.

If two loads are in parallel, will the current be the same or different through them?

[Susan Brown]

Yep! I just wanted you to see how Ohm’s Law equations can be used to think through these things when you aren’t sure. But a fuse is basically a switch, and therefore acts like a wire (essentially no resistance, thus no voltage drop), unless of course it blows open.

[Susan Brown]

I wrote my response only having seen your 69.99 answer.

The 0.014 is perhaps correct. Isn’t that essentially zero?

[Susan Brown]

Rt would usually designate the total resistance for a circuit. We’re just concerned with the fuse.

I didn’t say your answer wasn’t correct, but I want you to KNOW the answer, not just guess.

You need to think about what a fuse is. Is it a load with resistance? What is its role in a circuit?

[Susan Brown]

That’s right – and what would R (the resistance) be for a fuse?

[Susan Brown]

Hi Bryan,

Let’s check your answer with an equation. What is the typical Ohm’s Law equation that we would use to find voltage?

[Susan Brown]

Hi Heath,

Unit 5 is describing various characteristics of series circuits and parallel circuits.

When two or more loads are in series, you can add the resistances of the loads together to get a “total” resistance. This can be useful when calculating the circuit current, since the “total resistance” is what determines that.

However, when loads are in parallel with each other, we talk about “equivalent resistance”. It’s a similar concept – it’s a way of describing the overall resistance that is present from all of the loads combined. It’s more complicated than simply adding them together, however.

We show the formula for calculating equivalent resistance in Unit 5. But we also give the rule of thumb in the 3rd video in that unit (you can even see it in the thumbnail for the video!). That’s perhaps more important to know than doing the actual calculation.

Take a look at that information again in Unit 5, and see if you understand it. Let me know!

[Susan Brown]

Hi Myles,

It could be, but we aren’t asking for that level of diagnosis in this question. You don’t have enough info to be that specific.

We tell you in the problem statement: *NOTE* These are simplified diagrams. There may be other components in the circuit that aren’t shown.

This means your answer will be a more general conclusion about the nature of the failure, not exactly which component in the entire circuit is bad.

What we want is for you to tell us what you can determine about the failure first from the measurements in Figure 1 (with the additional knowledge that the element has continuity), and then how the measurements in Part 2 give you even more insight into where the problem lies.

Back to your question – what is the basic thing that zero Vac across a good load tells you?

[Susan Brown]

If you got the answers correct, they will add up to 120 vac (or perhaps 119, depending on how you rounded the number for current). Because the sum of the voltage drops of loads in series will always add up to the source voltage.

You should have a copy of the Ohm’s Law chart handy whenever you are taking a quiz or exam! (Or, just open the site up in another window so you can have that unit available to look at when you need it.)

[Susan Brown]

Hi Ladarius,

First of all – just want to make sure you had gotten the feedback that I had emailed to you about the Midterm.

I’m going to copy a bit of our text from Unit 8. Can you follow how we describe to calculate voltage drop? If there’s something that is still unclear, please let me know. (This will help me see if I need to improve how we teach this.)

Voltage Drop

Here’s the key concept with voltage drop: A voltage drop across a load is produced when current flows through that load.

When we talk about voltage drop, we’re always talking about a specific load that has current flowing thorough it. That’s why it makes no sense to talk about the voltage drop at a wall outlet that we’re checking with our meter, for example, because there’s no current flow and no load (the meter doesn’t count as a load– a good meter should never load the circuit enough to make a difference).

In the course of doing its work, a load will have a voltage drop across it that is proportional to the resistance of that load. Remember E = I * R. You have to keep straight here what this is referring to. For example, if you’re looking at the voltage drop across a load, you would look at

E(voltage drop across the load) = I(current flow through the load) * R(resistance of the load).

If you’re analyzing an entire circuit, you would look at:

E(source or line voltage) = I (total current flow through the circuit) * R(total resistance of ALL the loads in the circuit)

[Susan Brown]

You got it!

[Susan Brown]

That’s correct – so you can already see why the answer you chose is not correct.

Now think about the terms “direct” and “alternating” current. Why are those terms used? (Describe it in terms of the flow of electrons)

[Author]

Posts