Well, if you track your units they will tell you what units.Okay so the equation I've been working with is t = L/R but I'm told I need to re arrange it. Is there any chance someone could give me an example? I missed the lesson on this and all my tutor is pretty much saying is I need to re arrange the equation. Also dividing 160 by 5 what does that give me like I know it's 32 but what units.
Well, if you track your units they will tell you what units.
The 160 has units of milliseconds.
The 5 is just a number (it is how many time constants is generally considered sufficient to reach the final value for most practical purposes).
So you have (160 ms)/(5). What are the units of the result?
Still milliseconds?Well, if you track your units they will tell you what units.
The 160 has units of milliseconds.
The 5 is just a number (it is how many time constants is generally considered sufficient to reach the final value for most practical purposes).
So you have (160 ms)/(5). What are the units of the result?
Yep.Still milliseconds?
32 is not a time constant, it is a number. You need to multiply it by the proper units, namely milliseconds.So if I've got tau (32) and 470mH I can make R the subject and do 32 x 470 then I have my resistance? Which would equal to 15,040 milliohms or 15.04 ohms?
Considering that you (or someone on your behalf) is spending good money for you to be able to attend those lessons, hopefully you will do so whenever possible.Ugh I thought I was getting somewhere there. This will teach me not to miss lessons.
They also fail to convey the importance of time management skills which, it seems, are completely lacking in the student population. Waiting until the last minute to do a homework set or a research paper is an all to common occurrence. If you know at the outset that you have a problem, at least you have time to do something about it. Wait till the last minute and you are out of options.Considering that you (or someone on your behalf) is spending good money for you to be able to attend those lessons, hopefully you will do so whenever possible.
Having said that, it is a sad reality that most texts and professors of engineering fail miserably to give the issue of the proper use of units the attention they deserve. Personally, I think this is unforgivable given the extreme value they have in detecting errors and the extreme consequences that uncaught errors can (and have) had. But most text authors and college professors have little to no "real world" experience and only see units as a formality that deserves a bit of lip-service now and then.
True, but I certainly can't claim that I was guilty of it before, during, and after my college days and right up to today. But while I can relate and sympathize with excessive procrastination, that doesn't mean I should absolve it's practitioners from the consequences of their choices -- quite the opposite.They also fail to convey the importance of time management skills which, it seems, are completely lacking in the student population. Waiting until the last minute to do a homework set or a research paper is an all to common occurrence. If you know at the outset that you have a problem, at least you have time to do something about it. Wait till the last minute and you are out of options.
I have. I usually tell it in every class (not always, but usually) every semester. Doesn't seem to make a bit of difference (there's been a very small handful of exceptions over the years).WBahn,
Your story should be told .... Completely with the results you obtained, and have your successful students do the same. Maybe it might sink in a little. I know its an uphill battle.
Okay so the equation I've been working with is t = L/R but I'm told I need to re arrange it. Is there any chance someone could give me an example? I missed the lesson on this and all my tutor is pretty much saying is I need to re arrange the equation. Also dividing 160 by 5 what does that give me like I know it's 32 but what units.
Hi,So if I've got tau (32) and 470mH I can make R the subject and do 32 x 470 then I have my resistance? Which would equal to 15,040 milliohms or 15.04 ohms?
I'm have a similar story with the exception of even though I've attended all the classes, read all the notes and done all the problems...I still cram like there is no tomorrow for a test. I can't get a goodnight sleep until all the tests are over...The frustrating part for me, personally, is that when I returned to college after getting out of the service I was NOT a procrastinator -- I read and studied assigned chapters before class, I started work on assigned homework the day it was assigned (and usually finished it that same day) and stayed up as late as it took on Friday to have ALL of my assignments completely done. The result was remarkable -- I had the entire weekend free to do whatever I wanted to do (and without a moment's guilt over what I should be doing), I didn't study for any finals except one (diffy-Q), and I walked to an easy 4.0 despite taking 23 semester hours. It was, by far, the most enjoyable semester I had in my entire college career -- with the following semester running a close second.
But even knowing this, I still find myself putting things off until the last minute. Something that I hope to train out of my daughter!
Hello there, thank you for clearing this up for me. We don't really work on re arranging equations much at college to be fair so I'm pretty poor at it if I'm honest.Hi,
You got close but the algebraic manipulation was not exactly done right...that was the main error. Since you missed the lesson i'll provide some more information here. The only assumption is that 5 time constants provides enough time to reach a close enough value to the max because that gets the approximation error down to less than 1 percent and it's a whole number. This assumption could vary however depending on what your professor considers adequate for the course.
You started with 160ms and you reasoned that if that was 5 time constants then one time constant would be 32ms, and that was correct. But now we have the algebra with the formula:
t=L/R {t here is the time constant in units of seconds}
You need the value for R, so you need to first solve for R. Multiply both sides by R and we get:
t*R=L
divide by t and we get:
R=L/t
Now we have an equation for directly calculating R.
Checking the units as Wbahn suggests, we get:
Ohms=(V*s/A)/s=V/A=Ohms
so the units check out ok.
You would next use R=L/t to find the right value of the resistance. Surprisingly, it comes out close to what you got before which shows how you can get almost the right answer by doing it wrong sometimes.
by Jake Hertz
by Jake Hertz