Electronics World Calculus Test?

[Phil Allison]

Hi to all,

The September issue of the pommy EW magazine (formerly Wireless World) has
an article on basic calculus as applied to electronics. Wildly exciting
stuff. At the end there is a test for readers to do with the answers posted
elsewhere in the mag.

There are four maths questions that can be done with the aid of a pocket
calculator:

1. What is the Slew Rate of a 3 volt rms, 1 MHz sine wave ?

2. What is the current flowing in a 100 nF capacitor when the applied
voltage increases linearly from 0 to100 in 1.5 uS ?

3. What is the rms value of a repetitive 25 kHz rectangular voltage waveform
which is at 10 volts for 10 uS then 1 volt for the rest of each cycle ?

4. What is the rms power when the above waveform is applied to a 1 ohm
resistor ?



** The author of the article said that a group of recent graduate
engineers he interviewed for a design job struggled with the answers to some
or all these. Can you do better ?




............... Phil

 

[Geoff C]

In article <3f95b27d$0$21653$afc38c87@news.optusnet.com.au>,
philallison@optusnet.com.au says...

Hi to all,

The September issue of the pommy EW magazine (formerly Wireless World) has
an article on basic calculus as applied to electronics. Wildly exciting
stuff. At the end there is a test for readers to do with the answers posted
elsewhere in the mag.

There are four maths questions that can be done with the aid of a pocket
calculator:

1. What is the Slew Rate of a 3 volt rms, 1 MHz sine wave ?

2. What is the current flowing in a 100 nF capacitor when the applied
voltage increases linearly from 0 to100 in 1.5 uS ?

3. What is the rms value of a repetitive 25 kHz rectangular voltage waveform
which is at 10 volts for 10 uS then 1 volt for the rest of each cycle ?

4. What is the rms power when the above waveform is applied to a 1 ohm
resistor ?



** The author of the article said that a group of recent graduate
engineers he interviewed for a design job struggled with the answers to some
or all these. Can you do better ?




............... Phil




From the graduates I've interviewed in the past couple of

years, not many here could answer these questions either. I've
had to start asking graduates about zener diodes and ohms law
to find at least some sensible answers. Once I had a question
at the start of an interview process something like "What are
the main advantages/disadvantages of a swtchmode power
supply?". With really piss-weak answers, I had to start asking
"Have you heard of a switchmode power supply?".

 

[David L. Jones]

On Wed, 22 Oct 2003 12:14:24 +1000, Geoff C <nosppamhere@work.com>
wrote:

From the graduates I've interviewed in the past couple of
years, not many here could answer these questions either. I've
had to start asking graduates about zener diodes and ohms law
to find at least some sensible answers. Once I had a question
at the start of an interview process something like "What are
the main advantages/disadvantages of a swtchmode power
supply?". With really piss-weak answers, I had to start asking
"Have you heard of a switchmode power supply?".

Yep, same here.
Some really basic questions quickly sort out the morons from the ones
who have a clue. Stuff like not knowing what the beta of a transistor
is, the difference between TTL and CMOS, how to make a square wave
oscillator, being able to draw and explain a full wave rectifier
circuit etc. The hit rate on such basic questions is surprising poor,
even with people who have supposedly had design experience.
I interviewed a young but supposedly experienced "microcontroller
specialist" once who could not even name one brand of microcontroller.
The real kicker though was that he bought in his uni thesis
documentation to show off (a fairly simple 8051 lcd data logger), and
when questioned on it he didn't even know what chips did what.
A test I like, is to give them a schematic (with mixed digital and
analog) and ask them to tell me anything about it they can. The same
with a populated PCB. This gives me a good idea of the areas they are
good in, or if they have any clue at all.

Dave
---------------------------
(remove the "_" from my email address to reply)

 

[Franc Zabkar]

On Wed, 22 Oct 2003 08:26:24 +1000, "Phil Allison"
<philallison@optusnet.com.au> put finger to keyboard and composed:

Hi to all,

The September issue of the pommy EW magazine (formerly Wireless World) has
an article on basic calculus as applied to electronics. Wildly exciting
stuff. At the end there is a test for readers to do with the answers posted
elsewhere in the mag.

There are four maths questions that can be done with the aid of a pocket
calculator:

1. What is the Slew Rate of a 3 volt rms, 1 MHz sine wave ?

Let v(t) = 3 * 1.414 * sin (2 * pi * 1E6 * t)

Then dv/dt = 3 * 1.414 * 2 * pi * 1E6 * cos ()
dv/dt (max) = 3 * 1.414 * 2 * pi * 1E6 * 1
= 26.7 * 1E6 volts/sec

Therefore, the slew rate = 26.7 V/us

2. What is the current flowing in a 100 nF capacitor when the applied
voltage increases linearly from 0 to100 in 1.5 uS ?

I = C * dv/dt
= 100 * 1E-9 * 100/1.5E-6
= 10/1.5
= 6.67 amps DC

3. What is the rms value of a repetitive 25 kHz rectangular voltage waveform
which is at 10 volts for 10 uS then 1 volt for the rest of each cycle ?

Period of waveform = 1/25E3 = 40us

So the voltage is 10V for 10us (1/4 cycle) and 1V for 30us (3/4
cycle).

Therefore Vrms = sqrt (1/4 * 10^2 + 3/4 * 1^2)
= sqrt (25 + 0.75)
= 5.07 Vrms

4. What is the rms power when the above waveform is applied to a 1 ohm
resistor ?

P = Vrms * Vrms / R = 25.75 Watts

** The author of the article said that a group of recent graduate
engineers he interviewed for a design job struggled with the answers to some
or all these. Can you do better ?




............... Phil

- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Death Eater Dan]

Yep, same here.
Some really basic questions quickly sort out the morons from the ones
who have a clue. Stuff like not knowing what the beta of a transistor
is, the difference between TTL and CMOS, how to make a square wave
oscillator, being able to draw and explain a full wave rectifier
circuit etc. The hit rate on such basic questions is surprising poor,
even with people who have supposedly had design experience.
I interviewed a young but supposedly experienced "microcontroller
specialist" once who could not even name one brand of microcontroller.
The real kicker though was that he bought in his uni thesis
documentation to show off (a fairly simple 8051 lcd data logger), and
when questioned on it he didn't even know what chips did what.
A test I like, is to give them a schematic (with mixed digital and
analog) and ask them to tell me anything about it they can. The same
with a populated PCB. This gives me a good idea of the areas they are
good in, or if they have any clue at all.

Dave

I'm a 4th year student in microelectronics about to graduate and hearing
that is actually good for me, shouldn't be as hard to get a job as I
thought!

I will say that today the courses in engineering are really been driven in
different directions. We do a lot of work now on project management, law and
information technology. In my third year I was amazed that nearly the whole
class was unable to solder (this was the first time we were required to!). I
doubt more than a couple of people in my class (of about 60) would know how
to use a FET, or for that matter design any type of analog circuit based on
transistors. Nearly all of the work we do is based on computers and
microprocessor systems. During the entire degree I think I have designed
just two PCB boards that did not contain a microcontroller, and one of them
was a simple single transistor microwave amplifier.

 

[David L. Jones]

On Wed, 22 Oct 2003 19:29:31 +1000, "Death Eater Dan"
<DeathEater@Hogwarts.com> wrote:

Yep, same here.
Some really basic questions quickly sort out the morons from the ones
who have a clue. Stuff like not knowing what the beta of a transistor
is, the difference between TTL and CMOS, how to make a square wave
oscillator, being able to draw and explain a full wave rectifier
circuit etc. The hit rate on such basic questions is surprising poor,
even with people who have supposedly had design experience.
I interviewed a young but supposedly experienced "microcontroller
specialist" once who could not even name one brand of microcontroller.
The real kicker though was that he bought in his uni thesis
documentation to show off (a fairly simple 8051 lcd data logger), and
when questioned on it he didn't even know what chips did what.
A test I like, is to give them a schematic (with mixed digital and
analog) and ask them to tell me anything about it they can. The same
with a populated PCB. This gives me a good idea of the areas they are
good in, or if they have any clue at all.

Dave

I'm a 4th year student in microelectronics about to graduate and hearing
that is actually good for me, shouldn't be as hard to get a job as I
thought!

You'll be streets ahead!

I will say that today the courses in engineering are really been driven in
different directions. We do a lot of work now on project management, law and
information technology.

Yeah, at uni we did full on civil engineering, and even went on site
to learn how to use a theodolite - really useful stuff for an
electrical engineer. The first year or two is often a waste, and you
have to do all these unrelated courses "just in case" you decide to
change from electrical engineering to brain surgery. They make it as
easy and painless as possible...

In my third year I was amazed that nearly the whole
class was unable to solder (this was the first time we were required to!). I
doubt more than a couple of people in my class (of about 60) would know how
to use a FET, or for that matter design any type of analog circuit based on
transistors. Nearly all of the work we do is based on computers and
microprocessor systems. During the entire degree I think I have designed
just two PCB boards that did not contain a microcontroller, and one of them
was a simple single transistor microwave amplifier.

That's why most grads never go into actual electronics design, not
that they would have a clue, or would be the least bit interested
anyway.

Dave
---------------------------
(remove the "_" from my email address to reply)

 

[The real Andy]

"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3f95b27d$0$21653$afc38c87@news.optusnet.com.au...

Hi to all,

The September issue of the pommy EW magazine (formerly Wireless World) has
an article on basic calculus as applied to electronics. Wildly exciting
stuff. At the end there is a test for readers to do with the answers
posted
elsewhere in the mag.

I would like to hear about that mag, is it any good? Is it like SC or more
like Elektor?

There are four maths questions that can be done with the aid of a pocket
calculator:

Who needs a pocket calculator when you have Matlab?

1. What is the Slew Rate of a 3 volt rms, 1 MHz sine wave ?

2. What is the current flowing in a 100 nF capacitor when the applied
voltage increases linearly from 0 to100 in 1.5 uS ?

3. What is the rms value of a repetitive 25 kHz rectangular voltage
waveform
which is at 10 volts for 10 uS then 1 volt for the rest of each cycle ?

4. What is the rms power when the above waveform is applied to a 1 ohm
resistor ?

Hmmmm, time for another beer.

** The author of the article said that a group of recent graduate
engineers he interviewed for a design job struggled with the answers to
some
or all these. Can you do better ?

1 in 1000 graduates may be able to answer the questions. I probably could if
I wasn't so pissed an if my calculus book was in front of me. Maybe
I should go back and read the questions again, do I even need a book on
calculus? I think not. PS. Whats a capacitor.

 

[The real Andy]

"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:kphcpvk3v3le43saapi6qog1bm2lnb68c0@4ax.com...

1. What is the Slew Rate of a 3 volt rms, 1 MHz sine wave ?

Let v(t) = 3 * 1.414 * sin (2 * pi * 1E6 * t)

Then dv/dt = 3 * 1.414 * 2 * pi * 1E6 * cos ()
dv/dt (max) = 3 * 1.414 * 2 * pi * 1E6 * 1
= 26.7 * 1E6 volts/sec

Therefore, the slew rate = 26.7 V/us

Scary, i remember doing this in 1st year uni. I think that differentiation
just got progessively worse too. I would be fucked if i needed to remember
it off the top off my head now. Maybe frank cheated and read a book. I do
remember doing high order differentials now. I did enjoy engineering
materials though, i even got a 7 in that one. A bit better than my conceeded
pass in 1st year math.

 

[Phil Allison]

"The real Andy"


Phil A wrote:

The September issue of the pommy EW magazine (formerly Wireless World)
.......

I would like to hear about that mag, is it any good? Is it like SC or
more like Elector ?

** EW is the sort of electronics magazine that most hobbyists would not
like much. The editorial tone and general technical level is pitched much
more towards professional technicians and engineers. Many of the articles
are chock full of hairy looking maths !!!

The are a fair number of items relating to basic electronic component
behaviour and ( genuine ) hi-fi audio articles gets a good run since it
seems to be common ground for so many technical bods as their passionate
hobby.

Most Aussie newsagents stock it - or will get it in for you if you
ask them.




............ Phil

 

[cdb]

I would like to hear about that mag, is it any good? Is it like SC or more
like Elektor?
Wireless World (that dates me) is very much a theory based magazine, by that

I mean they don't always have complete projects, but info that would enable
someone to incorporate into another project. For example going back a year
or so - Making transmission lines out of co-ax and the maths required.

Probably closer to Circuit Cellar.

If you ever want to see IEEE's having a bun fight over whether a wire placed
at 89.9327 degrees versus one placed at 89.9911 would induce extra noise
into an amplifier - then the letters pages of this mag are for you!

In past years the person on the recieving end has been Doug Self - an audio
person

At present it is Ivor Catt who is receiving vitriole.

In Qld costs $11.20.

Colin


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.528 / Virus Database: 324 - Release Date: 16.October.2003

 

[Franc Zabkar]

On Wed, 22 Oct 2003 20:03:49 +1000, "The real Andy"
<ihatehifitrolls@yahoo.com.au> put finger to keyboard and composed:

"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:kphcpvk3v3le43saapi6qog1bm2lnb68c0@4ax.com...

1. What is the Slew Rate of a 3 volt rms, 1 MHz sine wave ?

Let v(t) = 3 * 1.414 * sin (2 * pi * 1E6 * t)

Then dv/dt = 3 * 1.414 * 2 * pi * 1E6 * cos ()
dv/dt (max) = 3 * 1.414 * 2 * pi * 1E6 * 1
= 26.7 * 1E6 volts/sec

Therefore, the slew rate = 26.7 V/us

Scary, i remember doing this in 1st year uni. I think that differentiation
just got progessively worse too. I would be fucked if i needed to remember
it off the top off my head now. Maybe frank cheated and read a book.

Maybe Franc's favourite subject was maths. And just maybe the
questions were really, really, really simple. After all, 1st year Uni
covers the *fundamentals*.

I do
remember doing high order differentials now.

The questions require a knowledge of first order differentials.

I did enjoy engineering
materials though, i even got a 7 in that one. A bit better than my conceeded
pass in 1st year math.

- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[The real Andy]

"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:7todpvs590gg6n84sm5v5ljnbcdrmdm4u6@4ax.com...

Scary, i remember doing this in 1st year uni. I think that
differentiation
just got progessively worse too. I would be fucked if i needed to
remember
it off the top off my head now. Maybe frank cheated and read a book.

Maybe Franc's favourite subject was maths. And just maybe the
questions were really, really, really simple. After all, 1st year Uni
covers the *fundamentals*.

Maybe Frank was one of those nerds that sat at home rather than drinking at
the campus club with all the other engineers!!

I do
remember doing high order differentials now.

The questions require a knowledge of first order differentials.

I'll be dammed if I can even remember them!!

 

[Mark Hathaway]

scary to think, Douglas Self is rather objective about things too.


Mark Hathaway

markhathawayREMOVEME@bigblue.net.au






"cdb" <barnDOTc@webcityuk.zznDOTcom> wrote in message
news:3f966591$0$4845$afc38c87@news.optusnet.com.au...

I would like to hear about that mag, is it any good? Is it like SC or
more
like Elektor?
Wireless World (that dates me) is very much a theory based magazine, by
that
I mean they don't always have complete projects, but info that would
enable
someone to incorporate into another project. For example going back a
year
or so - Making transmission lines out of co-ax and the maths required.

Probably closer to Circuit Cellar.

If you ever want to see IEEE's having a bun fight over whether a wire
placed
at 89.9327 degrees versus one placed at 89.9911 would induce extra noise
into an amplifier - then the letters pages of this mag are for you!

In past years the person on the recieving end has been Doug Self - an
audio
person

At present it is Ivor Catt who is receiving vitriole.

In Qld costs $11.20.

Colin


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.528 / Virus Database: 324 - Release Date: 16.October.2003

 

[Phil Allison]

"cdb"

At present it is Ivor Catt who is receiving vitriole.

** Who remembers Ivor Catt's famous nemesis - Ouida Dogg ??






...................... Phil

 

[Franc Zabkar]

On Thu, 23 Oct 2003 17:21:09 +1000, "The real Andy"
<ihatehifitrolls@yahoo.com.au> put finger to keyboard and composed:

"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:7todpvs590gg6n84sm5v5ljnbcdrmdm4u6@4ax.com...

Scary, i remember doing this in 1st year uni. I think that
differentiation
just got progessively worse too. I would be fucked if i needed to
remember
it off the top off my head now. Maybe frank cheated and read a book.

Maybe Franc's favourite subject was maths. And just maybe the
questions were really, really, really simple. After all, 1st year Uni
covers the *fundamentals*.

Maybe Frank was one of those nerds that sat at home rather than drinking at
the campus club with all the other engineers!!

To be honest, Uni wasn't the happiest time of my life. But I didn't
spend it studying, or drinking, at least not to excess. As for the
other would-be engineers, by the time 4th year came around there were
only about 100 of them left out of a starting lineup of ~400.

I do
remember doing high order differentials now.

The questions require a knowledge of first order differentials.

I'll be dammed if I can even remember them!!

Maybe it's because we were introduced to them way back in high school.
Pretty basic stuff, in fact ...


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[cdb]

Maybe it's because we were introduced to them way back in high school.
Pretty basic stuff, in fact ...

One of the problems with the way higher maths is sometimes taught in schools
(yes I can only talk about UK schools from 20 years or so ago), is that the
maths is presented in technical terms rather than relating it to ways that
it is used in normal life without a thought.
For example say to to a school kid - how far is the Gold Coast from your
house and they'll reply X amount, then you say 'ah yes, how long did it take
to get there?' reply about an hour, so what speed approx were you doing
them, X Klms per hour. the you say do this sum

v=dk/dt they'll go huh?

Colin



---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.528 / Virus Database: 324 - Release Date: 16.October.2003

 

[Mike Harding]

On Fri, 24 Oct 2003 07:37:37 +1000, "cdb"
<barnDOTc@webcityuk.zznDOTcom> wrote:

Maybe it's because we were introduced to them way back in high school.
Pretty basic stuff, in fact ...

One of the problems with the way higher maths is sometimes taught in schools
(yes I can only talk about UK schools from 20 years or so ago), is that the
maths is presented in technical terms rather than relating it to ways that
it is used in normal life without a thought.
For example say to to a school kid - how far is the Gold Coast from your
house and they'll reply X amount, then you say 'ah yes, how long did it take
to get there?' reply about an hour, so what speed approx were you doing
them, X Klms per hour. the you say do this sum

v=dk/dt they'll go huh?

Very good point. It wasn't until I started to do calculus that I
realised why I'd spent all those boring hours learning algebra
and calculus made a lot of sense when we proved that the
reasons food was put into cylindrical tins was that they were
the most efficient use of metal for such purposes. Absolutely,
relate maths to real life and it will make more sense for most
people.

Mike Harding

 

[The real Andy]

"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:bdbgpvk8hoich3dq079035rntccg7t1o5u@4ax.com...

On Thu, 23 Oct 2003 17:21:09 +1000, "The real Andy"
ihatehifitrolls@yahoo.com.au> put finger to keyboard and composed:

"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:7todpvs590gg6n84sm5v5ljnbcdrmdm4u6@4ax.com...

Scary, i remember doing this in 1st year uni. I think that
differentiation
just got progessively worse too. I would be fucked if i needed to
remember
it off the top off my head now. Maybe frank cheated and read a book.

Maybe Franc's favourite subject was maths. And just maybe the
questions were really, really, really simple. After all, 1st year Uni
covers the *fundamentals*.

Maybe Frank was one of those nerds that sat at home rather than drinking
at
the campus club with all the other engineers!!

To be honest, Uni wasn't the happiest time of my life. But I didn't
spend it studying, or drinking, at least not to excess. As for the
other would-be engineers, by the time 4th year came around there were
only about 100 of them left out of a starting lineup of ~400.

I think that is pretty common. Most of those high school students spend all
their time chatting in the lectures making it difficult for us mature-age
(not so mature in my case) students and the other kids that want to learn.
It seems that all the chatters' are the ones that drop out, much to the
relief of the ones who wish to learn.

I do
remember doing high order differentials now.

The questions require a knowledge of first order differentials.

I'll be dammed if I can even remember them!!

Maybe it's because we were introduced to them way back in high school.
Pretty basic stuff, in fact ...

Ahh, maybe that's the problem. I am one of those high school drop-outs that
really struggled with first year uni math.

 

[Tony Pearce]

"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:bdbgpvk8hoich3dq079035rntccg7t1o5u@4ax.com...

As for the
other would-be engineers, by the time 4th year came around there were
only about 100 of them left out of a starting lineup of ~400.

The others woke up and moved to courses leading to higher paying jobs?

TonyP.
(who dropped out of the course after coming top of the class in the first
two years)