Physics or electronics? Help!

[Ice.Maiden]

Could anyone please help with some vague time constant calculations? I know that T=CxR.

The questions set, are: 470mf x 100k (squiggle like an "n")
220mf x 1m ( " )
680mf x 2m ( " )
I assume the m's for million? but I don't even understand what's required!!
Thank you to anyone who can help!

[red-forest.]

Buenchico WoW nice answer Thank You.

[Ice.Maiden]

Not at all Chris. I admire someone with some brains.

[Ice.Maiden]

This post's closed now. Thank you for all your help. x

[DebsyDoo]

Looks like it could be "mu" one of the Greek symbols used in electronics (which in conjunction with "f" stands for micro farads) so, 220microfarads x 100 k ???
(would actually make more sense if it was like a "u" with a tail to the left)

Dunno if that helps at all

[mibn2cweus]

I'm sorry but I know dam well what mf stands for and it has ***** to do with capacitance.

MFD or mfd are regrettably occasionally used to designate �f (microfarad) but milli-farad if ever used at all should always be spelled out long-hand (including the hyphen) so that people can be positively certain about what an idiot the author who wrote it is. mf is totally ambiguous and same goes for the instructor using it as the length of this thread clearly demonstrates.

If one does not have ready access to this symbol � then this symbol u (that�s right, the letter u) is a perfectly acceptable substitute where capacitance is implied, as in:

470uf . . . (meaning �470 microfarad�)


Same goes for mΩ . . . what the ???? is that supposed to mean . . . milli-ohm?

Mega ohm is always, always written with an uppercase M . . . for example:

2MΩ . . . (meaning �two million ohms�).

For crying out loud, if a person can�t create a meaningful abbreviation then they should resort to spelling it out . . . in English . . . 4 heaven�s sakes!

And finally . . .

Why anyone would use such large values of capacitance in conjunction with such small values of resistance (especially those specified in the last two problems) in the context of an RC time constant circuit defies my wildest imagination. Under these circumstances I find all of the problems as written highly suspect . . . but then there is always the possibility that I just know too much! <"?

In any case, Chris (as usual) has provided the correct solutions for the problems as stated and if graded as incorrect I would demand restitution.

Rant over!

[beso]

mF is a milliFarad. However it is frequently used incorrectly for the more common microFarad which is supposed to be written as uF.

milli is 10^-6
micro is 10^-9

milliohms is quite a small resistance and the time will be very short.

Given the potential misuse of m for u they could be talking megohms MΩ

Ω is ascii 234 (Hold down ALT and type 234 on numeric keypad)

[beso]

Well mwbn (whatever dumb unmemorable name you chose) time constants can have any value. Yes in a delay circuit you would use a larger resistance but there are many occasions where the time constant can be in femtoseconds such as in a microchip.

Always spelling out micro is rubbish. The rules of metric are quite clear and there is no reason to divert from them for some special case of capacitance. Ludites frequently getting it wrong is no reason to bend a rule.

P peta 10^15
T terra 10^12
G giga 10^9
M mega 10^6
K kilo 10^3
m milli 10^-3
u micro 10^-6
n nano 10^-9
p pico 10^-12
f femto 10^-15

[beso]

Do you realise that Michael Faraday was the only scientist ever to get a unit named after both his names.

Microfarad.

Apparantly they also named one for his grandmother.

;-)

[kempie]

How do you know his grandmother was named Millie?

;-)

[mibn2cweus]

beso, If you can figure out how to cram half a Farad into a micro-chip you'll have my vote for the Nobel Prize ;o)

[imhotep]

Is Ice on AB tonight?
If you are Ice,how did you get on with the Time Constant calculations that you posted yesterday.
Were the posted answers helpful at all?

[Ice.Maiden]

Hi Imhotep - and others. Oh dear. What can I say! My friend's daughter was delighted to get some results....but ...she said Cjhris's answers weren't quite right! Please don't ask me what the correct answers were. I don't know - but everyone, myself included, said which we thought was right. I was just trying to help the girl, and I'm so damned glad that i've left school and don't have to worry about farads, etc! Lol - and cheers! x

[imhotep]

Phew,that's a relief then!!
Let's hope she doesn't have any more of those awkward questions again then.
Where's Albert Einstein when you need him eh?LOL
;-))

[Ice.Maiden]

I know. The thing is, I was really tired last night, and actually came up with some answers which tallied with others...but as I say, it seems Chris's answers weren't quite right either. They're the ones I used, since he used to teach. the info I gave was correct, so..... no idea then, but that table you sent was a good one. I just wasn't sure where to insert which figures! No - I DEFFO pleased that my school days are over, although I used to enjoy physics at the time.

[Ice.Maiden]

Doh. Sorry - this keyboard's rubbish, and letters keep disappearing or the wrong ones pop up!! Not my fault - honestly! : )

[Buenchico]

If 'Chris's answers weren't quite right' it's only because the information provided wasn't quite right either ;-)

I indicated that the answer to the first question looked ridiculous but I could only use the figures provided. Both Kempie and myself (later assisted by Mibn2cweus) pointed out that the units in the questions didn't fit in with 'real life' situations. However, the answers I provided fitted the 'weird' information in the questions precisely.

However, the reason I gave up teaching Physics, in favour of Maths, is that Maths is a 'pure' science which avoids all of the 'practical' problems associated with Physics! ;-)

Chris

[Buenchico]

Icey:
I've got a similar problem with my keyboard. Strangely, it only seems to occur when I've got to the bottom of the bottle. Hic! ;-)

[Ice.Maiden]

Hi Chris. Well thanks for the help anyway. I must admit that the info given seemed a bit vague - or so it looked to me last night. As I say, I passed your answers on, but I don't know what went wrong. I think the information must've been slightly out in some way.
Whatever, I was just trying to help - as everyone else was.
Thanks for what you did, anyway.

[imhotep]

Is it okay if I post another answer on your thread?

I would just like to say that I didn't do physics in my school.
I think I just learned about general science and some biology.I actually enjoyed my schooldays.It was only on my first day in school I was rather apprehensive and a little scared.But,after my first year I got more confident in my lessons.Fortunately, I did not get bullied at all.Although,during my first week in school,someone told me that there were bullies in the school.This older looking boy came up to me,and I think he was after my dinner money.But,instead of picking on me,he picked on my friend instead.I nearly felt like intervening,but I was worried I might get hurt.I can't remember much what happened,but I'm pretty sure he said something like I was such a cute scrawny little kid to be picked on.He was right about me being a bit scrawny though.My friend was a bit plumper than me.
I will never forget that first week in school!
My favourite subjects had to be Geography,Maths,Technical drawing,Music and athletics.
Oh well,I've waffled on quite a bit now.
It's getting a bit late for me now,so I am hopping off to me bed in a few moments.
So,night night Icey!
See you all again soon...
*0* Yawn....Night all!
xx

[Ice.Maiden]

No, of course i don't mind you being on the thread Imhotep. Interesting to see how some folk see their schooldays. I look back quite fondly on mine, despite saying that I'm glad I've left. I think you subjects you were interested in, are typical "male ones", somehow - you know, the maths, techie ones, etc. I took physics and biology - the phsyics because whatever other choice was available at the time was less interesting - the biology, because I loved it. I excelled at English though. That was my fave. You can tell me more another day if you're going to bed now. x
Chris - had to laugh about your keyboard bit. Wish mine WAS just the fault of an empty bottle, but it's just done-for.