ideas on how to understand this

gloria saidi

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Feb 10, 2012, 12:53:22 PM2/10/12

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I am studying this unit,"electromagnetic fields and waves" but i have
a problem since there are too many equations to derive which drives
me crazy.which method is the best for me to approach it?

mike

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Feb 10, 2012, 2:49:57 PM2/10/12

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If you're interested in a general overview of electromagnetic waves,
take a look at the "Radio Amateur's Handbook".

If you're taking a course and expect to pass it, you need to LEARN
the stuff that's gonna be on the test.
There's no substitute for learning the math required by the course.

Stated another way, if you don't want to learn the material,
don't take the class.

Tauno Voipio

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Feb 10, 2012, 3:44:28 PM2/10/12

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On 10.2.12 9:49 , mike wrote:
> On 2/10/2012 9:53 AM, gloria saidi wrote:
>> I am studying this unit,"electromagnetic fields and waves" but i have
>> a problem since there are too many equations to derive which drives
>> me crazy.which method is the best for me to approach it?
>
> If you're interested in a general overview of electromagnetic waves,
> take a look at the "Radio Amateur's Handbook".
>

The book is currently called The ARRL Handbook.

--

Tauno Voipio, OH2UG

Tim Wescott

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Feb 10, 2012, 4:28:53 PM2/10/12

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As stated: if you want to pass the class, suck it up and learn the
stuff. Or, at least, memorize it long enough to get a C.

E&M is classic theoretical physics: a few governing equations, and a
whole lot of conclusions that can be drawn from them. E&M -- in a
classroom setting -- is all about starting from those four little old
equations by Maxwell, doing a s**tload of math, and finding out something
about the world that you didn't know before.

On the bright side, I know plenty of working engineers that just barely
scraped by E&M and went on to brilliant careers in industry -- while
there are a few jobs that demand that you understand that stuff, most
just require you to remember a few of the derived factoids.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

mike

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Feb 10, 2012, 5:11:20 PM2/10/12

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Agree completely. There are obvious exceptions, but for many projects,
lots of math is a sign that the engineer either doesn't understand the
problem or technology or both,
or is trying to use the wrong technology. Also will result in
manufacturing issues.
If it takes six digit precision to make it work, it's gonna be difficult
to make them on a production line.

But you still gotta pass the class to get the degree that gets the job.

Phil Hobbs

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Feb 10, 2012, 6:36:47 PM2/10/12

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If going round and round in the same groove is okay with you, you can
ignore the math. Otherwise not. Every new thing I've ever done, with
one or two exceptions, took a bunch of math to get going. Even new
classes of circuits--one reason that analogue folks are getting rarer is
that you can't do good analogue design just by poking SPICE till
something seems to work.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

John Fields

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Feb 10, 2012, 6:36:38 PM2/10/12

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---
Read the course material over and over again, ask your instructor and
your peers for help, and visit your local library.

--
JF

Tim Wescott

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Feb 10, 2012, 7:16:48 PM2/10/12

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Many, perhaps, but not all -- much of my business involves doing projects
that the folks that can't handle lots of math can't even start on.

But -- if I find myself needing six digits of precision to get things to
work, then I do make a point to have a long conversation with the
customer that mentions the words "feasibility", "practicality" and "cost"
quite a few times.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

John Fields

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Feb 10, 2012, 7:17:55 PM2/10/12

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---
Mine is titled: "The ARRL Handbook For Radio Amateurs"

What's the newest one called?

--
JF

Tim Wescott

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Feb 10, 2012, 7:21:36 PM2/10/12

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One of my customers is an entirely self-taught circuit designer, and is
doing brilliant things. Of course, he's good at identifying the bits
where he's weak, and he shoots that stuff off to me to vet.

> Every new thing I've ever done, with
> one or two exceptions, took a bunch of math to get going. Even new
> classes of circuits--one reason that analogue folks are getting rarer is
> that you can't do good analogue design just by poking SPICE till
> something seems to work.

I find that (usually), once I understand something I don't need to flog a
whole bunch of math to get it to all come together. But initially I most
certainly do.

_Not_ being able to do the math, and just being a blind "SPICE jockey" is
certainly a road to error -- but then, I've known some pretty good analog
circuit designers who couldn't go from an op-amp circuit to a transfer
function to save their lives, but knew _exactly_ how to simulate that
circuit in SPICE so that they'd be sure it'd work in real life.

Jim Thompson

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Feb 10, 2012, 7:35:42 PM2/10/12

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On Fri, 10 Feb 2012 18:21:36 -0600, Tim Wescott <t...@seemywebsite.com>

Phil Hobbs

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Feb 10, 2012, 7:44:40 PM2/10/12

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SPICE is a good and useful thing, but when you use it as a substitute
for thought, it limits you and you eventually get in trouble. (Google
for "one trick pony".) ;)

I have no doubt that a highly intelligent but nonmathematical person
might be able to do everything in Horowitz & Hill, and then some. Win
Hill himself is an example, if I'm not mistaken, and so was Jim
Williams.

But if you re-read Jim's piece on his CCFL backlight work of 20 or so
years ago, it's hard not to think, "Jim, you know, an afternoon's worth
of analytic math would have saved you six months' pain."

Another example is the essential difference between heaters and Peltier
coolers for temperature stabilization, which is not obvious without
doing the math, at least in outline: heater-based systems are far more
vulnerable to thermal forcing in general, because the heat leak has to
equal the average heater power plus device dissipation, whereas a
Peltier or phase-change (cryogenic) system can be as well insulated as
you like.

And in my business, before trying something new, I always have to grind
through a feasibility calculation, which is always analytical. Probably
a quarter of my business is doing photon budgets for smart,
well-educated folks who aren't confident enough to do it for
themselves. Practice!

Cheers

Phil Hobbs

> --
> My liberal friends think I'm a conservative kook.
> My conservative friends think I'm a liberal kook.
> Why am I not happy that they have found common ground?
>
> Tim Wescott, Communications, Control, Circuits & Software
> http://www.wescottdesign.com

bitrex

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Feb 10, 2012, 7:56:24 PM2/10/12

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> might be able to do everything in Horowitz& Hill, and then some. Win

> Hill himself is an example, if I'm not mistaken, and so was Jim
> Williams.
>
> But if you re-read Jim's piece on his CCFL backlight work of 20 or so
> years ago, it's hard not to think, "Jim, you know, an afternoon's worth
> of analytic math would have saved you six months' pain."
>
> Another example is the essential difference between heaters and Peltier
> coolers for temperature stabilization, which is not obvious without
> doing the math, at least in outline: heater-based systems are far more
> vulnerable to thermal forcing in general, because the heat leak has to
> equal the average heater power plus device dissipation, whereas a
> Peltier or phase-change (cryogenic) system can be as well insulated as
> you like.
>
> And in my business, before trying something new, I always have to grind
> through a feasibility calculation, which is always analytical. Probably
> a quarter of my business is doing photon budgets for smart,
> well-educated folks who aren't confident enough to do it for
> themselves. Practice!
>
> Cheers
>
> Phil Hobbs
>

I messed around with something for a few hours in LTSpice - I then
dragged out Routh-Hurwitz and found out in twenty minutes that what I
was trying to do wasn't possible. Doh!

Phil Hobbs

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Feb 10, 2012, 8:37:34 PM2/10/12

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Douglas Adams called those things "recreational impossibilities". ;)

In my first engineering job, I spent a whole day trying to build a phase
shifter whose phase vs. frequency slope was positive--in other words, as
I later realized, a time machine. (I had to stabilize my fancy PLL the
hard way.)

Cheers

Phil Hobbs

George Herold

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Feb 10, 2012, 9:04:02 PM2/10/12

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Are you an undergard? First or second year? E&M was one of my
favorite courses. There's a few basic equations. And lot's of ways
to apply them.
For any course you've got to get the basic's done pat.
You can't just memorize some derivations.
Electro statics and Magneto 'statics' are built on pieces of Maxwells
equations. The course is traditionally taught historically so you
don't get to the full equations till the end of the course.
If you're learning vector calculus at the same time you're learning
E&M then the math can be a bit overwhelming... but in some ways
getting the math down... curls and gradients and all, may be more
useful.

George H.

George Herold

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Feb 10, 2012, 9:10:54 PM2/10/12

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> But you still gotta pass the class to get the degree that gets the job.- Hide quoted text -
>
> - Show quoted text -

I'm not sure Tim was saying you didn't need math?

My notebooks are cover in (roughly) equal parts, Math, drawings, and
circuits... though lots of time the math becomes stapled in pages.

George H.

George Herold

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Feb 10, 2012, 9:29:54 PM2/10/12

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On Feb 10, 7:44 pm, Phil Hobbs

You just gotta use some math to calculate the size of the heat fin you
need for the Peltier. :^)

>
> And in my business, before trying something new, I always have to grind
> through a feasibility calculation, which is always analytical. Probably
> a quarter of my business is doing photon budgets for smart,
> well-educated folks who aren't confident enough to do it for
> themselves. Practice!

It's amazing how many people won't try and calculate something.
I often make mistakes... but then the measurement points out an
error... and I learn something. If I'd just been poking around I'd
learn nothing at all... except for that one instance.

George H.

>
> Cheers
>
> Phil Hobbs
>
> > --
> > My liberal friends think I'm a conservative kook.
> > My conservative friends think I'm a liberal kook.
> > Why am I not happy that they have found common ground?
>
> > Tim Wescott, Communications, Control, Circuits & Software
> >http://www.wescottdesign.com
>
> --
> Dr Philip C D Hobbs
> Principal Consultant
> ElectroOptical Innovations LLC
> Optics, Electro-optics, Photonics, Analog Electronics
>
> 160 North State Road #203
> Briarcliff Manor NY 10510
> 845-480-2058
>

> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

Phil Hobbs

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Feb 10, 2012, 9:57:39 PM2/10/12

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You probably do need scientific notation for that, it's true. ;)

> >
> > And in my business, before trying something new, I always have to grind
> > through a feasibility calculation, which is always analytical. Probably
> > a quarter of my business is doing photon budgets for smart,
> > well-educated folks who aren't confident enough to do it for
> > themselves. Practice!
>
> It's amazing how many people won't try and calculate something.
> I often make mistakes... but then the measurement points out an
> error... and I learn something. If I'd just been poking around I'd
> learn nothing at all... except for that one instance.

Even when their livelihoods depend on it working, which is the really
astounding thing.

Cheers

Phil Hobbs

Ken S. Tucker

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Feb 10, 2012, 11:14:53 PM2/10/12

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Mostly obtain a good 'intuitive' understanding of how antennae
transmit and receive, then as you study Maxwells Equations,
the partial diffs wrt time, and the 'curl' convention will make
sense, and will likely garner your respect.
Learn too how a speaker can be a microphone.
Ken

mike

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Feb 10, 2012, 11:34:45 PM2/10/12

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I'm not saying you don't need any math. I'm saying that it's easy to try to
use too much math in the initial stages.
Math is only as useful as the equations you write and the numbers you
plug in.
Spice is a design verification tool, not a synthesis tool.

The gain of a common emitter transistor amplifier is Rc/Re.
With that knowledge and an understanding of gain-bandwidth product,
an ENGINEER can easily decide how many stages are needed and the
appropriate devices to use. You then start tweaking that basic
design to account for the more subtle aspects and for stability.
THEN you plug it into spice to determine
if you were correct, and possibly refine further.

Give the same problem to a SPICE JOCKEY and you're likely to get
fewer stages with higher gains sitting on the edge of stability.
Bean counters love the fewer parts. Manufacturing managers, not so much.
The spice jockey is less likely to have those "leaps" that are the
stuff of technical advancement and patents. They're less likely to
recognize when the design requirements and acceptance criteria are
incomplete.
Hint, that's always.
They're too busy tweaking the component values on the wrong spice model.

As a mentor, would you rather teach spice to an engineer or try
to teach engineering to a spice jockey?
I've never been very successful at the latter. If they made it thru
college without the engineering mentality, they're probably not ever
gonna get it. Real engineers are rare, and they're formed very early
in life.

Math good...basic understanding much better.

Don Lancaster

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Feb 10, 2012, 11:38:35 PM2/10/12

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< http://www.tinaja.com/glib/rebound1.pdf >

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: d...@tinaja.com

Please visit my GURU's LAIR web site at http://www.tinaja.com

Mr.CRC

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Feb 11, 2012, 12:50:50 AM2/11/12

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Very hard work.

It took me 20 hrs/week of study to earn an A in E&M. I had to review
completely all the math before hand, mostly the relevant vector calc.
which was nicely covered in the text.

My favorite part was the transmission line chapters, which fortunately
in the course I took, was heavily emphasized. I learned a great deal.
Doing all the homework, and not just to get the answers, but exploring
tangential questions which arise, was also essential in driving it home.

I wish the course had the time to get deeper into the propagation of
waves through various media & boundaries, since that topic is basically
the physics of optics, which is also heavily involved in my work with
lasers.

If I had had to take this course along with several others in a
full-time curriculum, I may have not been able to study it to the depth
that I did. Rather, I took it as a one-off paid by my employer.

Of course, I forget most of it anyway, but the course together with
considerable time scoping at the bench with fast logic gates driving
coax cables did give me a decent understanding of signal propagation
enough to fix most cabling problems caused by clueless scientists, and
to design decent PCBs and cable drivers.

I could pick up the more rigorous stuff like bounce diagrams and Smith
Charts in a few hours of review if I actually needed to do these things
again.

E&M is extremely valuable subject to master at the introductory level at
least once, so that the insights into proper physics can guide your
reasoning throughout the rest of your career--assuming you do some sort
of electrical engineering.

Good day!

--
_____________________
Mr.CRC
crobc...@REMOVETHISsbcglobal.net
SuSE 10.3 Linux 2.6.22.17

Tim Wescott

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Feb 11, 2012, 1:19:51 AM2/11/12

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Actually, all I was trying to say that if you find E&M hard and
unrewarding, it's not time to either slit your wrists or change your
major to business management -- just that you should grit your teeth and
get through the class with a passing grade, then don't take any jobs that
involve optics, lasers, or microwaves.

(I don't speak from direct experience, by the way. I loved E&M, much to
the disgust of most of my classmates. I wasn't a super student
academically -- but I coached the A students through the mathematically
intense classes. It was only after I graduated and got a job that I
realized that not everyone has to be a whiz at the hard math -- as long
as the group is seeded with people who are, or who can get the job done
without it).

mike

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Feb 11, 2012, 2:03:19 AM2/11/12

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You sound like the roommate who got me thru calculus 101...by the skin
of my teeth.

Jim Thompson

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Feb 11, 2012, 10:54:07 AM2/11/12

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Sonnova gun! You couldn't make a "predictor" ?:-)

Phil Hobbs

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Feb 11, 2012, 11:15:33 AM2/11/12

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I was trying to use the usual op amp all-pass network, i.e. +1 at low
frequency, -1 at high frequency, only using an inductor instead of a
capacitor. I blew a sign in the math--for that circuit the phase shift
is opposite, but the gain is -1 at low frequency and +1 at high
frequency, so the phase slope is the same as in the capacitor case.

(I'd just got my bachelor's degree in astronomy, and hadn't connected
the Kramers-Kronig relations to circuits yet. Fortunately I learned
fast.)

Don Lancaster

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Feb 11, 2012, 12:50:35 PM2/11/12

to

On 2/10/2012 7:10 PM, George Herold wrote:
>-
>
> I'm not sure Tim was saying you didn't need math?
>
> My notebooks are cover in (roughly) equal parts, Math, drawings, and
> circuits... though lots of time the math becomes stapled in pages.
>
> George H.

Given enough heresy, virtually all of the math in electromagnetic fields
can be eliminated entirely.

Phil Hobbs

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Feb 11, 2012, 12:59:26 PM2/11/12

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Don Lancaster wrote:
>
> On 2/10/2012 7:10 PM, George Herold wrote:
> >-
> >
> > I'm not sure Tim was saying you didn't need math?
> >
> > My notebooks are cover in (roughly) equal parts, Math, drawings, and
> > circuits... though lots of time the math becomes stapled in pages.
> >
> > George H.
>
> Given enough heresy, virtually all of the math in electromagnetic fields
> can be eliminated entirely.
>
> < http://www.tinaja.com/glib/rebound1.pdf >

Number crunching isn't heresy, it's the default SPICE jockey approach.
It isn't a substitute for analysis, and it isn't new. In fact, we did
almost this exact thing in my undergraduate physics lab course in about
1979, using one of the original Data General Novas. It's sort of cute
doing it in PostScript, but Matlab or Octave would do it faster and give
you similar-looking graphs.

brent

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Feb 11, 2012, 1:02:39 PM2/11/12

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On Feb 10, 12:53 pm, gloria saidi <gloriasaid...@gmail.com> wrote:
> I am studying this unit,"electromagnetic fields and waves" but i have
> a problem since there are too many equations to derive which drives
> me crazy.which method is the best for me to approach it?

Best method is to learn enough to pass the test, then spend the rest
of your life learning it for real.

brent

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Feb 11, 2012, 1:10:26 PM2/11/12

to

I completely agree with every word you wrote.

Jim Thompson

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Feb 11, 2012, 1:24:37 PM2/11/12

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Yep. If I ever stop _learning_ new tricks, it'll be because I'm dead
>:-}

Michael A. Terrell

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Feb 11, 2012, 2:16:24 PM2/11/12

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Jim Thompson wrote:
>
> On Sat, 11 Feb 2012 10:02:39 -0800 (PST), brent
> <bule...@columbus.rr.com> wrote:
>
> >On Feb 10, 12:53 pm, gloria saidi <gloriasaid...@gmail.com> wrote:
> >> I am studying this unit,"electromagnetic fields and waves" but i have
> >> a problem since there are too many equations to derive which drives
> >> me crazy.which method is the best for me to approach it?
> >
> >Best method is to learn enough to pass the test, then spend the rest
> >of your life learning it for real.
>
> Yep. If I ever stop _learning_ new tricks, it'll be because I'm dead
> >:-}

AKA: One step beyond 'Slomanized'. :(

--
You can't have a sense of humor, if you have no sense.

George Herold

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Feb 11, 2012, 2:42:07 PM2/11/12

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Understood, most of my class mates hated E&M too.
I petioned to take it early,
(There was a 'good' prof. teaching it and a 'blow hard' the next
year.)

>
> (I don't speak from direct experience, by the way. I loved E&M, much to
> the disgust of most of my classmates. I wasn't a super student
> academically -- but I coached the A students through the mathematically
> intense classes. It was only after I graduated and got a job that I
> realized that not everyone has to be a whiz at the hard math -- as long
> as the group is seeded with people who are, or who can get the job done
> without it).

I'm very far from a math whiz, but I love thinking in three
dimensions, and there's a lot of that in E&M.

George H.

>
> --
> My liberal friends think I'm a conservative kook.
> My conservative friends think I'm a liberal kook.
> Why am I not happy that they have found common ground?
>

> Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com- Hide quoted text -

George Herold

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Feb 11, 2012, 2:57:15 PM2/11/12

to

Thanks Don, I find the math is important, not to solve some
complicated boundary value problem. But as a way to think about the
world. The are zillions of examples of the same math solving
different problems.

Most of the time my 'math' is just guesstimating some area, and a
length, with some time constant involved.

George H.