# who to trust Cecil or a physics teacher... **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [April 14, 2002, 4:47am UTC](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533 "2002-04-14T04:47:27Z")\ **Posts on this page:** 9\ **Page:** 3
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [September 12, 2003, 9:00pm UTC](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533/41 "2003-09-12T21:00:37Z")
> [@](#): > > \*Originally posted by Mogadon \* > Well, we covered multi-strand wire earlier - the skin effect is quite pronounced by 1 Mhz and above. A good example of the need for multi-strand here is loudspeaker wire. You send 1Mhz to your loudspeakers? What does that sound like? :eek: ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [September 13, 2003, 1:49am UTC](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533/42 "2003-09-13T01:49:46Z")
Sorry but that teacher quite definitely **was not** talking about anything other than normal wires used for mains power or whatever. The guy was a fruitloop. Myself and other guys in the class would often have to explain to him that what he was telling us contradicted basic concepts from the text books he was supposed to be teaching us from. Luckily he was not the type of guy to be offended (don’t get me wrong, nice guy, just not the brightest bulb in the box). And as for the science teacher who reckoned you could see the speed of light, he was not talking about any special equipment, he was talking about naked eye, and suggested we try out and “prove” his bizarro theory by watching carefully that night in our respective bedrooms. ---
**Author:** ![Mogadon](https://avatars.discourse-cdn.com/v4/letter/m/7feea3/32.png) [@Mogadon](https://boards.straightdope.com/u/Mogadon)\ **Post date:** [September 14, 2003, 1:09pm UTC](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533/43 "2003-09-14T13:09:27Z")
quote: Originally posted by Mogadon Well, we covered multi-strand wire earlier - the skin effect is quite pronounced by 1 Mhz and above. A good example of the need for multi-strand here is loudspeaker wire. You send 1Mhz to your loudspeakers? What does that sound like? … Higheeeeee! But seriously, I don’t say that I want maximum current flow to my speakers (or, more likely, a pizeo transducer) at 1 Mhz+. It’s just that at that frequency you are using about 1/100 of the thickness of the wire. At about 100k I would guess you might be using about 1/3 the thickness of a typical cable, pro rata as you get lower. In most of the audio bands the numerical effect is not very marked, unless you are using cable several inches thick, but it would probably affect the balance between high and low notes. I leave the production of more precise figures as an exercise for my readers - and to forestall any other questions; we are assuming copper wire, and though we know the current actually falls off exponentially from the surface to the centre, we will not claim that we therefore use all of the wire! ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [September 14, 2003, 1:50pm UTC](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533/44 "2003-09-14T13:50:28Z")
**Mogadon,** any calculations you are doing at 1MHz or even 100K are not very relevant to audio frequencies, which to the human ear, stop around 20K at the high end. From [Skin Effect Relevance in Speaker Cables:](http://www.audioholics.com/techtips/audioprinciples/interconnects/SkinEffect_Cables.htm) > [@](#): > > While Skin Effect is a real world problem in high frequency applications such as RF Power and Transmission, it is negligible at audio frequencies… If you want to discuss this further, I suggest starting a new thread on the topic, as this one should be devoted to the Sound of Quackers. [Julie Andrews]“The hills are alive…”[/Julie Andrews] ---
**Author:** ![AbbySthrnAccent](https://avatars.discourse-cdn.com/v4/letter/a/eb9ed0/32.png) [@AbbySthrnAccent](https://boards.straightdope.com/u/AbbySthrnAccent)\ **Post date:** [September 14, 2003, 1:58pm UTC](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533/45 "2003-09-14T13:58:22Z")
> [@](#): > > \*Originally posted by Mogadon \* > I find this an odd idea. Surely asking your school is like asking your mother for a reference - most of the time it will be marvellous, occasionally it might be accurate, but you won’t be able to trust it at all. \*\* Many colleges and universities in the U.S. use Grade Point Average and class rank, which are impacted by your class room grades, as well as college board exam scores in admission decisions. ---
**Author:** ![Mogadon](https://avatars.discourse-cdn.com/v4/letter/m/7feea3/32.png) [@Mogadon](https://boards.straightdope.com/u/Mogadon)\ **Post date:** [September 14, 2003, 9:45pm UTC](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533/46 "2003-09-14T21:45:50Z")
“Mogadon, any calculations you are doing at 1MHz or even 100K are not very relevant to audio frequencies, which to the human ear, stop around 20K at the high end…If you want to discuss this further, I suggest starting a new thread on the topic…” * * * As I tried to say before, I am not trying to have a discussion about skin effects and audio lines! I just picked an example application where I guessed there might be some effect - the point of the topic was whether a physics teacher was right when he claimed that electricity only travelled on the surface of the wires. Your cite suggests the effect is low even at the top end of human hearing - about 3% - and I would be happy to withdraw the word ‘good’ from ‘good example’; it was only a guess, after all. My point is still that there were some circumstances where the teacher’s words might make sense - and Princhester has told us that these did not apply, anyway. … “Many colleges and universities in the U.S. use Grade Point Average and class rank, which are impacted by your class room grades, as well as college board exam scores in admission decisions.” … As I mentioned above, this sounds very strange to someone brought up on externally moderated exams - doesn’t anyone point out the problems with such a system? ---
**Author:** ![AbbySthrnAccent](https://avatars.discourse-cdn.com/v4/letter/a/eb9ed0/32.png) [@AbbySthrnAccent](https://boards.straightdope.com/u/AbbySthrnAccent)\ **Post date:** [September 14, 2003, 11:29pm UTC](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533/47 "2003-09-14T23:29:09Z")
> [@](#): > > \*Originally posted by Mogadon \* > As I mentioned above, this sounds very strange to someone brought up on externally moderated exams - doesn’t anyone point out the problems with such a system? \*\* Why no, you are the first to think of it. What a grand idea. Thank you. :rolleyes: ---
**Author:** ![The\_Ryan](https://avatars.discourse-cdn.com/v4/letter/t/7feea3/32.png) [@The\_Ryan](https://boards.straightdope.com/u/The_Ryan)\ **Post date:** [September 22, 2003, 11:17pm UTC](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533/48 "2003-09-22T23:17:24Z")
> [@](#): > > \*Originally posted by Mogadon \* > I find this an odd idea. Surely asking your school is like asking your mother for a reference - most of the time it will be marvellous, occasionally it might be accurate, but you won’t be able to trust it at all. If a school were to give all of its students 4.0, universities would notice that and take it into account. They aren’t stupid. They realize that a 3.4 at a prep school that takes only the smartest students and holds them to demanding standards is better than 3.8 at some feel good school where everyone who shows up every day gets at lest a B. In fact, often class rank is used instead of GPA. Isn’t ability to get good grades a better indicator of ability to get good grades than ability to take tests? If someone has a perfect score on the SATs, but a GPA of 2.5, the conclusion that most universities come to is that he may be smart, but he’s lazy and not willing to do the work required to succeed. ---
**Author:** ![Manduck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/manduck/32/256_2.png) [@Manduck](https://boards.straightdope.com/u/Manduck)\ **Post date:** [September 23, 2003, 2:00am UTC](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533/49 "2003-09-23T02:00:14Z")
My high school physics teacher told us that The Towering Inferno is a great movie. [Previous page](https://boards.straightdope.com/t/who-to-trust-cecil-or-a-physics-teacher/103533.md?page=2)