Susan Brown

[Susan Brown]

I have 120 volts
I enter 5 ohms of resistance
I get current of 24 and power of 2880

This is not correct?

This would be correct only if the 5 ohm load is the ONLY load in the circuit.

The current in a series circuit, which is the same throughout the circuit, is determined by the total resistance of the loads in the circuit. In this case, that is 5005 ohms.

If you have 5005 ohms and 120volts, what will the circuit current be?

Then use that current to figure out how much wattage is produced by each load.

(There’s no record of a Reset Request from you, but I did just set you back to this unit.)

[Susan Brown]

How do you do that quote thingggy?

1. Copy and paste the text you want to quote into the reply box.
2. Highlight it.
3. Click “B-Quote” in the tool bar at the top of the reply box.

[Susan Brown]

Hi Desert,

The easiest way to figure this out is to just look at the Ohm’s Law equation for Power that involves resistance and circuit current, P = I^2 x R (current squared times resistance)

Power is directly proportional to resistance. When resistance goes up, power goes up.

Then all you have to do to answer this question is see how much R1 is greater or smaller than R2, and that will be the same amount that P1 is greater or smaller than P2.

The reason we know that your approach was mistaken in some way is that you got a much higher wattage for a very small load – that doesn’t make sense. If you were trying to use the formula P = E^2/R, the value for voltage (E) has to be the voltage drop across the load in question. The voltage drop across a 5 ohm load will be MUCH smaller than the drop across the 5k ohm load.

[Susan Brown]

HI Bailey,

Yes, with NTC, if the temperature goes up, the resistance decreases. Or if the temperature decreases, the resistance increases. In other words, they move oppositely.

So when you dunk the probe in ice water, you are making the temperature decrease. This means the resistance will increase.

That’s what we’re saying in the question. Does that make sense?

[Susan Brown]

Hi OwlGuy!
Are you looking at the Household Electrical Power Supply video? (Some people mistakenly count the “Safety, Mon!” photo as a video.)

It’s at about the 11 minute, 50 second mark of that video.

[Susan Brown]

Hi Ali,
Thanks for posting in the Forums!

Question 10 is asking about AC voltage, not current. You can figure out the answer to this if you think about polarity. Remember, DC is “direct current”. It has one direction, thus a positive and a negative side to the power supply (like a battery). AC is “alternating current”, and moves back and forth, as you have learned. When you read DC voltage, as the video in this unit showed you, you’ll either get a + or – sign as part of the measurement. Do you also get that with AC voltage measurements?

Question 21 – from unit 7

In general, the two types of voltages you will measure (aside from AC and DC) are:

– Power voltages: these are used to drive the loads that do the appliance’s work– motors, heaters, lights, etc. These are usually AC line voltages.

– Control voltages: these are uses to control power voltages. Examples are digital data logic lines. These are usually DC voltages.

[Susan Brown]

Hi Jared,

Thanks for posting a question!

Question #2 asks about DC current. The part you copied from the lesson is talking about DC voltage.

Very different things!

From Unit 7:

The three most common electrical measurements you’ll be doing as a professional appliantologist are:

– Voltage, either DC or AC
– Resistance and its daughter test, Continuity
– AC current, which is always done with a clamp-on amp meter (or ammeter). (Note: You will never need to measure DC current in appliance repair.)

[Susan Brown]

Okay – it sounds like you’ve got it figured out. I’ll reset that quiz for you. Feel free to ask more questions in these Forums as needed!

[Susan Brown]

Hi Josh,

Thanks for posting a question!

A great video to review is the one at the end of Unit 3 in Basic Electricity. The one about the heat produced by a loose connection. Watch that and see if you can duplicate the calculation on your own. If there are any steps that you don’t understand, let me know here and we’ll discuss it further.

Let me know if that helps.

[Susan Brown]

Hi Mike,

Fundamentals has taught you the basics of reading schematics. But that’s like learning to read music. You will need to practice in order to get more “fluent”.

Oven & Range Repair and Advanced Troubleshooting have the most practice on schematics compared to the Refrigerator course.

Then, once you’re done with the courses, many of our webinar recordings over at Appliantology give you more exposure.

[Susan Brown]

Hi Josiah,

Did you see the explanation that showed up after you took the quiz?

Although it is true that a heating element is composed of high-resistance wire, this is not what makes it a load. For example, a heating element in a box sitting on the shelf is also made of high resistance wire but it is not a load because it isn’t in a circuit with current flowing through it.

A load in the context of appliance repair is:
– technically speaking, a component that does work – produces motion, heat, light, etc. – when it gets power
– electrically speaking, a component that produces a voltage drop when current flows through it.

[Susan Brown]

It’s just a humorous one-question quiz. 🙂

[Susan Brown]

Hi Mike,

It’s not so much of what type of learner you are, it’s more that you just need to practice. That’s true for everyone who takes our courses. You have to practice to really get everything to click and to gain proficiency.

We suggest starting with your own appliances. Get the tech sheets and compare them with what you see. Look for free or cheap appliances that are banged up or even broken (Craigslist, town dump, etc.). Use Appliantology to get the tech documents and start playing around.

The only way to post an image directly in these Forums is if the image is on a website and you can give the link. You can also just email the photo to us and we can upload it here.

[Susan Brown]

Just did!

[Susan Brown]

Hi Mike,

Good question! If you re-listen to that part of the video, Samurai mentions that the power company is trying to deliver a certain amount of power along the lines. And we know that Power = Current x Voltage (P=IxE). So if you have a certain goal for the amount of power you want to deliver, the higher your voltage, the lower the current needs to be.

But you are correct that if we are looking at a circuit, and it’s got a fixed resistance, if you changed the voltage supply from a 120vac to a 240vac, then the current would increase according to I = E/R.

But, say you need to generate 1000 watts of power. Play around with the numbers, using P=IxE. What would the current need to be if you used a 120 vac supply and then a 240vac supply? You’d need half as much current if you use 240vac.

Make sense? There are various “moving parts” to creating the electrical situation that an engineer wants in a circuit: power, voltage, current, and resistance. And they all act according to Ohm’s Law equations!

[Author]

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