Susan Brown

[Susan Brown]

Did you watch the videos at the end of Unit 4? We cover this exact scenario.

Remember, you got part 1 correct on your exam. In our question, the diode fails open. So we want you to tell us what happens to the current when that failure happens. In other words, the circuit was operating correctly then had that failure. So, it goes from having current to having no current.

You also got part 2 correct.

3. The fan motor is the only load in that particular circuit. And the resistance of the motor is what it is – it can’t change. Rule of thumb – what happens in one parallel circuit doesn’t affect others that are in parallel. (The overall current will change.)

Part 4 is correct.

[Susan Brown]

You’ve got this correct now! The 3 answers add up to 119, which is close enough. It’s just off a little because of rounding of numbers along the way.

[Susan Brown]

Hi Ronny,

Glad to help! Loads will only split up the voltage drop if they are in series with each other, but the ignitor and booster are in parallel with each other. Plus, we didn’t give you any idea of what the resistances are of the loads to know how to divide them up.

Hmmmmm….

This question trips up a lot of folks, but once you see what’s going on, you’ll have an “a-ha!” moment. I’ll help step you through.

First, try doing the “Zen trick” on the booster. How do you reach N?

[Susan Brown]

Hi Zachary,

If you go back to the Operational Overview video in unit 2, starting around 1 minute or so, you’ll hear that the refrigerant enters the evaporator as a liquid. It absorbs heat from the air and then boils and turns into a gas.

Does that help?

[Susan Brown]

Look at the video again, for example around the 10 minute mark, and again later in the video, his discussion about Cam 6. When those contacts are closed, what is being supplied to the motor windings?

[Susan Brown]

Yes, that works.

[Susan Brown]

Hi Sajjad,

Do you know how timer contacts work? They open or close a circuit for one or more loads. So, they are either supplying L1, L2, or Neutral to a load, depending on the configuration.

[Susan Brown]

Hi Ronny,

I think you’re just mixing up the math

He’s telling you that the resistance of R1 is two times that of R2.

So, whatever R2’s resistance is, R1 will be two times that. If R2 is 10, R1 would be 20. If R2 is 50, R1 would be 100.

Since we know that R1 + R2 has to equal the voltage supply (120), then there is only one pair of values that will meet both criteria:

R1 = 2 x R2

AND

R1 + R2 = 120.

R1 = 80
R2 = 40

[R1 + (2 x R2) = 120 is not a correct way to rewrite the equation. You could substitute (2 x R2) for R1 and write (2 x R2) + R2 = 120. This then equals 3 x R2 = 120, which gives us R2 = 40.]

Does that help?

[Susan Brown]

Thanks for the head’s up!

Would you please tell me which course, module and unit that appeared in so I can fix that link? Thank you!

[Susan Brown]

Hi Rodney,

1. you are close! remember that an electrical circuit has to end up where it started. Your need to select the answer that adds “module” at the end.

2. “What current carriers are present in a gas flame with a voltage difference across it?”

When you have a flame, you’ll have both electrons and ions. We show that in a couple of places in the video.

[Susan Brown]

It does take some thinking and working in order to figure this stuff out!

Think of parallel circuits as individual series circuits that are tied to the same power supply.

When we are talking about parallel circuits, we often refer to different “branches”. Each branch is actually a little series circuit.

So, each individual series circuit will follow the rules of series circuits. However, when there are two or more circuits (or branches) in parallel, the total current to/from the power supply will be the combination of the current flow in each branch.

Look at the figure below. Each branch (B, C, D) is an individual series circuit. The resistance of the load in each circuit will determine the current in that circuit.

If you had more than one load in any of the branches, then the total resistance in that branch would determine the current flow in that branch.

In this figure, if each load is identical, then the current in B, C, and D would be the same.

The sum of the currents in B, C, and D would equal the current flow found at points A. So, A = B+C+D

This is only true for current.
Does that help?

[Susan Brown]

Hi Michael,

There were 3 correct answers (we asked you to select all that apply)
LoZ setting on your DMM
Wiggy or solenoid voltage tester
Any low input impedance meter that measures AC voltage

You had only answered wiggy and solenoid tester

[Susan Brown]

You are correct! I reset you.

[Susan Brown]

Hi Ronny,

You’ll learn a lot more about series and parallel circuits in the next two units.

The current is the same throughout a series circuit.

In parallel circuits, what happens in one does not affect the others.

Current is determined by the voltage supplied and the total resistance in the circuit. Those two items are not affected by something happening in a circuit that is parallel to it.

See the last two videos in Unit 4!

Let us know if you have any followup questions.

[Susan Brown]

Hi Ronny,

Answers will vary slightly depending on how you round the numbers.

There is no practical difference between 1350 and 1352 watts from our (appliance techs) point of view.

[Author]

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