Should I stick it out in EE with weak-ish math?

[BuddhaBelly34]

The only thing that concerns me is THROUGH/ACROSS. I am not sure I understand the difference.

Still Googling the topics you listed for your FE candidates. Trying not to overload my brain.

 

[psparky]

The only thing that concerns me is THROUGH/ACROSS. I am not sure I understand the difference.

Still Googling the topics you listed for your FE candidates. Trying not to overload my brain.

Good question...I'll try to explain.

When I take a volt meter and what to measure the voltage across a resistor...I take one terminal and place it on one side of the resistor and I take the other terminal of the volt meter and I place is ACROSS the resistor. So the positive terminal of the volt meter is on one side of the resistor...and the negative terminal is on the other side of the resistor. The votage reading is then taken ACROSS the resistor.

If I want to take an amp meter and find the current THROUGH the resistor. I need to disconnect a wire to the resistor...lets say the positive terminal of the battery. Now I need to hook this to the amp meter (which has two terminals or wires as well). Now I take the other wire of the amp meter and hook it back up to the original resistor. The current must now go THROUGH the amp meter.

Voltage is always measured across...current is always measured through...

Questions?

 

[psparky]

That's where the thru and across come from. Even when you are NOT using volt or amp meters and are just talking about the mathematics of a circuit...you still use the terms ACROSS and THROUGH correctly or you will sound silly!

If you don't quite understand yet...it's fine. As we cover more terms and concepts...it will become clear.

Also...as you can see...you math skills are more than adequate!

 

[psparky]

You are probably wondering the difference between voltage and current like most people do. I could explain in a complicated way...but instead I will explain in simple terms. Using a water example is good in my opinion.

Say I have a fire truck connected to a fire hydrant. Let's say this fire truck has an advanced control system for controlling water pressure and flow.

Ok...lets say they hook a garden hose up to it and simulate the flow you have at your house and they spray you in the chest. No biggy...your used to that.

Now let's say they increase the pressure of that same garden hose and spray you in the chest...it hurts much more. This is the same as increasing voltage! Increasing voltage is like increasing the "pressure" of a circuit.

Now let's say they go back to the original pressure of your garden hose...except this time they you going to use a garden hose that is 5" is diameter. Now when the hose gets sprayed at you...you get walloped by the massive water flow. This is the same as increasing current in a ciruit! More flow!

Now let's say I use the 5" garden hose with increased pressure and flow and hit you in the chest...you go flying backwards...This is the same as increased voltage and increased amperage! And incidentally...as you increase amperage...you need to increase wire size accordingly. Going to higher voltages will not increase wire size...it will only increase the insulation around the wire to keep the wire from arcing...or shorting.

This leads us into our next equation.

P=IV

Power = Current X Volts

Power is measured in Watts.

 

[BuddhaBelly34]

That makes perfect sense! I think I may have been measuring current incorrectly. With the above statement, if you measure current from one end of the resistor to the other you wouldn't get the same reading would you?

Damn my lab professor with his laissez-faire attitude toward teaching.

@ the second topic
Now it makes sense why amperage kills and not voltage. Increased flow of electricity allows the stopping of the heart, at even low voltages. So it's current = amount, voltage = intensity?

P=IV good lord I hope everything stays so easy.

 

[psparky]

That makes perfect sense! I think I may have been measuring current incorrectly. With the above statement, if you measure current from one end of the resistor to the other you wouldn't get the same reading would you?

Damn my lab professor with his laissez-faire attitude toward teaching.

@ the second topic
Now it makes sense why amperage kills and not voltage. Increased flow of electricity allows the stopping of the heart, at even low voltages. So it's current = amount, voltage = intensity?

P=IV good lord I hope everything stays so easy.

Correct...if you put the amp meter in parallel...you have effectively made a current divider...which doesn't tell you jack. The rest of your comments sound correct as well.

 

[psparky]

Here's another power equation...P=(I^2)*R. It's simply derived from plugging the V=IR into P=IV.

P=I*(I*R)

Also...(V^2)/R=P

Okay...KVL and KCL

Kirchoff's voltage law...Kirchoff's current law.

KVL...the sum of the voltages across the load or loads in a single loop equals the voltage source.

KCL...current in equals current out of a node.

 

[BuddhaBelly34]

This makes so much sense as to why I couldn't explain my results in my lab report. And I still got an A. I hate grades. They make no sense.

I speak with a lot of the Nepalese students in my classes and they tell me about their experience with school in Nepal. All I have to say is, holy crap. It's actually an accomplishment to pass high school there.

Okay, so with P=IV what does that tell us? Say a PSU for a PC. If I have a 650w PSU what does that mean? That it can send only a total of 650w (probably peak) across all of it's wires combined, or that it can send a total of 650w down each wire? Does what you say hold true for all PSUs?

Thanks so much for all of your help!

 

[psparky]

Lets talk about series and paralell. Let's use water for a teaching tool again.

When two resistors are in series...the water must flow thru one resistor...then thru the other resistor.

When two resistors are in parallel...the water must flow thru both resistors at the same time.

Capeche?

 

[BuddhaBelly34]

Got it.

 

[psparky]

This makes so much sense as to why I couldn't explain my results in my lab report. And I still got an A. I hate grades. They make no sense.

I speak with a lot of the Nepalese students in my classes and they tell me about their experience with school in Nepal. All I have to say is, holy crap. It's actually an accomplishment to pass high school there.

Okay, so with P=IV what does that tell us? Say a PSU for a PC. If I have a 650w PSU what does that mean? That it can send only a total of 650w (probably peak) across all of it's wires combined, or that it can send a total of 650w down each wire? Does what you say hold true for all PSUs?

Thanks so much for all of your help!

Not sure what a PSU is. But watts make more sense when calculated across a load...not thru wires or individual wires.

 

[psparky]

So let's finish up with the basics. First of all...when you have a voltage source with two resistors in series...the current thru the resistors is ALWAYS identical. If there is two amps thru the first resistor...there is two amps thru the second resistor even if their resistances are different. Once you find the current...You can then find the voltage across each resistor...and you will notice that KVL and KCL are satisfied...also that V=IR no matter how you slice it.

Series resistance...simply add the two resistors together to get there equivalent resistance.

Paralell resistance is slighter more complicated. (R1 X R2)/(R1 +R2)

 

[psparky]

Last two topics to complete your foundation for EE. Never forget this stuff!

Voltage division and current division.

When you have two resistors in series...they will often ask you what the voltage is across one of the resistors.

I'll say it two ways. When finding the voltage across a resistor in series with another resistor...take the resitor you are interested in and divide it by the sum of the two resistors...then multiply it by the voltage source.

Here's the same thing with term. If you are looking for the voltage across R1

Voltage source X ((R1/(R1+R2))= Voltage across R1

When all voltages are found...again you will find that V=IR...KCL and KVL are satisfied.

 

[psparky]

Current division is typically when you have a current source in parallel with two resistors in parralel. In other words...how much current goes thru each resistor. If both resistors are equal...current splits equally.

It's identical to the voltage division...except you take the resistor you are NOT intersted in...and divide by the sum of the two resistors.

If you want the current thru R1...Current source X ((R2/R1+R2))

It gets tricky...but if you take the currents you found in both branches and multiply by their resistors...the voltages will be equal! If the voltages are not equal...you did something wrong!

V=IR...KVL and KCL are satisfied.

Even in the dreaded AC...all these things are the same!

That's it for now. Master these concepts and you can pretty much get through 50% of your electrical engineering courses!
Practice, practice problems. Things will start clicking more and more!

 

[earlofwessex]

Very good explanations psparky!

Okay, so with P=IV what does that tell us? Say a PSU for a PC. If I have a 650w PSU what does that mean? That it can send only a total of 650w (probably peak) across all of it's wires combined, or that it can send a total of 650w down each wire? Does what you say hold true for all PSUs?

just to catch this, PSU is a power supply.
that 650W value should¹ be RMS, and it can supply a total of that when you add up all the loads². note that power is delivered over two wires, since it involves a voltage (which has to be between two places). almost universally in DC systems, the black wire is the return, called ground.
for eg: the potential difference will be between the Red and black wires, and the current will flow from the red wire through the load and back through the black wire (in the other direction, remember KCL?). these values give you your I and V for the eqn.

---
¹Marketing/sales people will use any figure they can to make something sound better
²Things are actually a little more complicated than this, but the concept is what's important at the moment.

 

[BuddhaBelly34]

Very good explanations psparky!


just to catch this, PSU is a power supply.
that 650W value should¹ be RMS, and it can supply a total of that when you add up all the loads². note that power is delivered over two wires, since it involves a voltage (which has to be between two places). almost universally in DC systems, the black wire is the return, called ground.
for eg: the potential difference will be between the Red and black wires, and the current will flow from the red wire through the load and back through the black wire (in the other direction, remember KCL?). these values give you your I and V for the eqn.

---
¹Marketing/sales people will use any figure they can to make something sound better
²Things are actually a little more complicated than this, but the concept is what's important at the moment.

Thanks for that. Yehp PSU = power supply unit. Also, note 1 is very laugh worthy. To the point that a certification process needs to be done on units to make sure they do what they claim.

And I'm still reading through everything sparky.

 

[psparky]

And I'm still reading through everything sparky.

Take your time. Considering I just gave you 50% of EE...Im guessing it's going to take a while to digest. You won't get the full understanding until you start working sample problems...and you start struggling and asking questions. That's where the learning takes place.

Oh ya...forgot one more basic. (There are several details for sure...but you have a good start) When you have batteries hooked up in series...the you simply add the voltages of the batteries. So two 12 volt batteries in series will deliver 24 volts. When you have two batteries in parallel...the voltage remains the same...just the batteries will last roughly twice as long.

One good definition of "in parallel"...is "the voltage across is the same." So whenever you have 2 or more loads (resistors) in parallel...the voltage will be the same across each load. If the voltage is not the same...they are not in parallel.

 

[BuddhaBelly34]

Take your time. Considering I just gave you 50% of EE...Im guessing it's going to take a while to digest. You won't get the full understanding until you start working sample problems...and you start struggling and asking questions. That's where the learning takes place.

Oh ya...forgot one more basic. (There are several details for sure...but you have a good start) When you have batteries hooked up in series...the you simply add the voltages of the batteries. So two 12 volt batteries in series will deliver 24 volts. When you have two batteries in parallel...the voltage remains the same...just the batteries will last roughly twice as long.

One good definition of "in parallel"...is "the voltage across is the same." So whenever you have 2 or more loads (resistors) in parallel...the voltage will be the same across each load. If the voltage is not the same...they are not in parallel.

I knew that about the batteries from doing some simple electronics stuff at home.

 

[SophusLies]

Considering I just gave you 50% of EE...Im guessing it's going to take a while to digest.

More like 5%. The EE students that I met in school were math and physics freaks. Some more math and some more physics but they certainly weren't just V = iR kids. They all knew a ridiculous amount of Fourier-stuff, complex analysis, vector calculus, PDE's (for Maxwell's equations), and probability.

I would not take EE lightly for math. I'm not trying to scare you but you're going to see some very serious math in an EE curriculum. When I saw the EE kids in my upper level math or physics classes they thoroughly impressed me with their talents. When I took set theory we had an EE kid that absolutely destroyed the class. When I asked him what he was doing to master the things in the class he told me he learned most of this stuff indirectly in his digital logic design classes, lol.

 

[BuddhaBelly34]

More like 5%. The EE students that I met in school were math and physics freaks. Some more math and some more physics but they certainly weren't just V = iR kids. They all knew a ridiculous amount of Fourier-stuff, complex analysis, vector calculus, PDE's (for Maxwell's equations), and probability.

I would not take EE lightly for math. I'm not trying to scare you but you're going to see some very serious math in an EE curriculum. When I saw the EE kids in my upper level math or physics classes they thoroughly impressed me with their talents. When I took set theory we had an EE kid that absolutely destroyed the class. When I asked him what he was doing to master the things in the class he told me he learned most of this stuff indirectly in his digital logic design classes, lol.

It doesn't scare me to learn upper level math, I just wanted to make sure that losing a negative sign now and again, or integrating one of the trig co-functions to be positive, etc... wouldn't be the death of me in the field.

 

[psparky]

More like 5%. The EE students that I met in school were math and physics freaks. Some more math and some more physics but they certainly weren't just V = iR kids. They all knew a ridiculous amount of Fourier-stuff, complex analysis, vector calculus, PDE's (for Maxwell's equations), and probability.

I respect your opinion...and it's great to know all the stuff you described...but for 99% of us electrical engineers...it's not really going to be used in our work career.

EE's and physics guys are definietly two compeltely different animals. I did complete the EE program...and recently took the FE and PE. The principals I described above are 50% of school...the FE...and the PE. Yes, I'm speaking from experience. AC isn't all that different to me because V=IR in either case! Haha!...sorry, but as long as I'm this forum...i will never get away from that!

And sure those concepts above can be learned fairly quickly...however...mastering them will take years. And yes, the circuits you get in all the tests are going to be way more complicated then I described...but if you master those basic rules you can go a long, long way. And obviously learning way beyond that is goal...but for this young man...he hasn't even started his first day...but I wanted to give him a clear approach to what is coming...because proffesors are generally clear as mud.

 

[SophusLies]

I respect your opinion...and it's great to know all the stuff you described...but for 99% of us electrical engineers...it's not really going to be used in our work career.

I see what you mean. I agree that in a job you won't use that much from school.

 

[BuddhaBelly34]

but I wanted to give him a clear approach to what is coming...because proffesors are generally clear as mud.

so very true it hurts

my lab professor has some sort of disdain for teaching. he pushed back a lab so that we can, essentially, google the concepts.

 

[sophiecentaur]

Voltage is Potential Difference - the difference between the Potential on one side and the potential on the other (= Across the gap). Nothing is 'going through' - until you give it a path. Then Current flows Through the load you connected.

If someone says "I had 240V going through me" then their language is more shocking than the experience they had!

 

[sweetpotato]

As a practicing EE, IMO psparky gave the OP 50% of EE *that you will use on the job*, but about 10% of the EE they will expect you to know at school.

 

[BuddhaBelly34]

My first professor told me that getting his undergrad in EE was harder than both of his graduate degrees in the field. Do you guys feel the same?

 

[sweetpotato]

My first professor told me that getting his undergrad in EE was harder than both of his graduate degrees in the field. Do you guys feel the same?

I just have an undergrad in EE so can't really help there.

However, you need to keep in mind there are many reasons why this professor found it so hard. Did he have inadequate high school preparation? Was it hard for him to develop good study habits? You really can't draw any conclusions from that one statement alone.

 

[BuddhaBelly34]

He said that he "studied" by literally copying down the book word for word. So I would say his method of studying is rote learning.

Maybe he's just crazy. Cool guy though.

 

[psparky]

He said that he "studied" by literally copying down the book word for word. So I would say his method of studying is rote learning.

Maybe he's just crazy. Cool guy though.

The "harder" your courses are, the better for you in the long run. You are only going to work as hard as your prof's push you.

After you get your job...your GPA doesn't mean jack squat.

However, what you actually learned will matter imensely in the real world.

 

[real10]

To the original poster,
I just took the GRE recently and ended up with 760 on the math section...so yeah don't lose hope if u didnt do as well in high school...people end up doing better later on down the road...(i did better at penn state compared to HS and same thing with gre compared to HS) so yeah...depending on your undergrad institutions strength (my guess top 25 eng schools)...a B at min (of course higher the better) can signal u have understanding of the subject matter...a mix of A & B is def not bad at all by any means in engineering esp electrical eng...
and u can always work in some other field once u have a eng background... (maybe add a bus or liberal art minor maybe even linguistics lol)