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Engineering Thread

Brian

We really should have our own forum entirely, but I think a thread'll do.

I rather enjoy the relaxed nature of a thread derailment, but in the general public's interest, maybe we should all hang out here.

tl;dr TR032 ARE GO!

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Jonathan

1E6 – PF – Electricity and Magnetism

(1) Armature: In electrical engineering, an armature is one of the two principal electrical components of an electro-mechanical machine, i.e.: a motor/generator. The other principal is field winding or field magnet.

(2) Amplitude Modulation (AM): The encoding of a carrier wave by variation of the amplitude in accordance with the input signal.

(3) Back emf: A voltage induced into an inductor due to an alternating or pulsating current. The counter emf is always in polarity, opposing the applied voltage.

(4) Baseband: A band of frequencies occupied by all transmitted signals used to modulate the radio waves.

(5) Bandwidth: The numerical difference between the upper and lower frequencies of a band of electromagnetic radiation, especially an assigned range of radio frequencies.

(6) Carrier wave: An electromagnetic wave that modulates, as in frequency, amplitude, or phase to transmit speech, sound, images, and other signals.

(7) Commutator: An cylindrical arrangement of metal bars connected to the coil of a dc electric motor or generator providing a unidirectional current from the generator or a reversal of current into the coils of the motor.

(8) Depth of Modulation: In directive systems employing overlapping lobes with modulated signals, a ratio obtained by subtracting from the percentage of modulation of the larger signal, the percentage of modulation of the smaller signal, and then dividing by 100.

(9) D Layer: The lowest region of the ionosphere existing only during the day extending from about 40km to 65km above the earth. Also known as the D region.

(10) E Layer: Another region in the ionosphere extending from about 90km to 150km above the earth influencing long-distance communication by strongly reflecting radio waves in the range or 1MHz to 3MHz. Also known as the E region or Heaviside layer.

(11) F Layer: The highest region of the ionosphere extending at night from about 190km to 400 km and extending during the day from about 145km to 400km above the earth. Also known as the F region.

(12) DSB: An amplitude modulation in which the modulated wave is composed by the carrier, the upper sideband whose frequency is the sum of the carrier and the modulation frequencies, the lower sideband whose frequency is the difference between the carrier and modulation frequencies. Stands for double sideband. DSB-TC modulation = Double sideband transmitted-carrier modulation.

(13) DSBSC: Double sideband suppressed-carrier transmission. A transmission in which
1. Frequencies produced by the amplitude modulation are symmetrically spaced above and below the carrier frequency
2. The carrier level is reduced to its lowest practical level, ideally completely suppressed.

(14) Eddy currents: An electric current induced within the body of a conductor where the conductor either moves through a non uniform electric field or it is in a region where there is a change in magnetic flux. Also known as the Foucault current.

(15) Electromotive Force: The energy per unit charge that is converted reversibly from one form of energy into electrical energy in a battery or dynamo.

(16) Envelope: A curve that bounds another curve or a set of curves as the modulation envelope of an amplitude-modulated carrier wave.

(17) Faraday's Law of Induction: A Voltage induced across a conductor which moves at right angles through a magnetic field is proportional to the velocity of that moving conductor.

(18) Fleming's Rules: 1. LHR: First finger represents the direction of the field. Second finger represents the direction of current. The thumb represents the resultant motion.
2. RHR: Thumb represents the direction of motion of the conductor. The first finger represents the direction of the field and the second finger represents the direction of the current.

(19) Frequency Modulation (FM): The encoding of a carrier wave by variation of the frequency in accordance with the input signal.

(20) Folded Dipole: A dipole antenna whose outer ends are folded back and joined at the centre, with an impedance of 300ohms compared to the 70ohms of a single wire dipole, widely used in TVs and frequency modulation receivers.

(21) Ground Wave: A radio wave that travels along the surface of the earth.

(22) Heterodyning: In telecommunications, heterodyning is the new generation of frequencies by mixing two or more signals in a nonlinear device such as a vacuum tube, a transistor, or a diode mixer. The mixing of each two frequencies results in the creation of two new frequencies, one being the sum of the two frequencies mixed, the other being the difference.

(23) Intermediate Frequency (IF): A frequency produced by combining the received signal with that of the local oscillator in a superheterodyne receiver.

(24) Ionosphere: A region of the earth's atmosphere where ionisation is caused by incoming solar radiation affects the transmission of radio waves. It extends from about 70km to about 400km above the earth's surface.

(25) Isotropic radiator: A theoretical point source of waves that exhibits the same magnitude or properties when measured in all directions. It has no preferred direction of radiation. It radiates uniformly in all direction over a sphere centred on the source. It is a reference radiator with which other sources are compared. They obey Lambert's Law.

(26) Lap Winding: A two-layer winding in which each coil is connected in series to the adjacent coil.

(27) Lenz's Law: For a current induced in a conductor, the current is in such a direction that its own magnetic field opposes the change that produced it.

(28) Magnetomotive Force: The work that would be required to carry a hypothetical isolated magnetic pole of unit strength completely around a magnetic circuit.

(30) Permeability: In electromagnetism, permeability is the degree of magnetisation of a material that responds linearly to an applied magnetic field. Its sign is mu.

(31) Rotor: It was designed to reproduce audio frequencies from near 0Hz - 20Hz.

(32) Reluctance: A measure of the opposition of magnetic flux to electric resistance.

(33) Series Wound Motor: A commutator-type motor having armature and field windings in series. Its characteristics are it has a high starting torque, and its speed varies due to load.

(34) Shunt-Wound Motor: A Motor having the armature and field windings in parallel.

(35) Sideband: Either of the two band of frequencies, one just above and one just below the carrier frequency, that are a result of the modulation of the carrier wave.

(36) Sky wave: A radio wave that travels upward.

(38) Slip-Rings: A metal ring mounted onto the rotating part of a machine that provides a continuous electrical connection through brushes of stationary contacts.

Peleus

thanks jmc/baza!

just going through the mechanics there. anyone else not have a clue about corriolis acceleration etc??? i looked up coriolis in the university physics book and it wasn't there. Not a good sign...

TheAmateur

Peleus wrote: »

thanks jmc/baza!

just going through the mechanics there. anyone else not have a clue about corriolis acceleration etc??? i looked up coriolis in the university physics book and it wasn't there. Not a good sign...

Yep I've pretty much given up on those questions...

Jonathan

Has IS given notes for his 1e6 section this year? He didnt last year, but I found notes from the previous lecturer from the year before if ye are interested?

devinejay

We got some slides, haven't looked at them yet so I'm not sure how useful they might be. Any extra notes are welcome though,

Peleus

ha, i just realised i actually went to some mechanics lectures and have notes. I always just assumed that i just didnt go to the lectures for any of the stuff on the mechancis course i didnt understand. Although there are a load of gaps.

Jonathan

http://jmccrohan.com/public/1e6.zip

password: boardsie

I don't know how much of that is still on the syllabus/relevant.

TheAmateur

Jonathan wrote: »

Has IS given notes for his 1e6 section this year? He didnt last year, but I found notes from the previous lecturer from the year before if ye are interested?

That's what we got. I don't think it'll make much of a difference based on his past exam questions. They're pretty crazy.

Jonathan

TheAmateur wrote: »

That's what we got. I don't think it'll make much of a difference based on his past exam questions. They're pretty crazy.

We got none of that.

When someone asked, they were told, "I am a phyicist, not a printer" apparently.

Brian

Coriolis acceleration is -2ωv. That's all I know, and I'm sticking with that.

Peleus

hey whats the answer to this?

attachment.php?attachmentid=80162&stc=1&d=1242590278

I thought it was D. I got that by getting the moment caused by the stuff to the right of C. do you need to take the other stuff into account?

Peleus

TheAmateur wrote: »

Yep I've pretty much given up on those questions...

doubt you need to know any of that. You could get a first in mechanics by just studying the applied maths leaving cert course.

Brian

Peleus wrote: »

doubt you need to know any of that. You could get a first in mechanics by just studying the applied maths leaving cert course.

That is the hope to which I am grasping.

Brian

I also think it's D. But I'm not very good at moments.

TheAmateur

pretty sure its D too, can't see why you'd have to take the other stuff into account if you have a FBD cut exactly at point C... Is D not the given answer or something?
Did anyone do Q.4 of the 2008 exam? I got E but the answers we were given say B?

Peleus

Ye i did it. The answer is B (9.0)

for constant speed, F = Frictional force

Ffrict= uN.
N=mg
Ffric=(0.3)(3)(10) - says take 10 for g
therefore F = 9N. (B)

you probably said 0.3x3=1 giving 10 (ie E).

Oh an in response to the moment question, ye i think its D. i dont think the other stuff would have any affect on C. Do you think the exam will be basically the same as the last two years?

TheAmateur

Peleus wrote: »

you probably said 0.3x3=1 giving 10 (ie E).

Do you think the exam will be basically the same as the last two years?

Yep that's what I did alright!:o The exam qs seem pretty consistent through the two years, an even split between statics and dynamics and an even split between simple remember the formula qs and crazy abstract qs.
Did you do q. 9 in the 2007 exam by any chance? I got D in that one, just want to see if what I did was right (added the two momentums and divided by time because u was in the opposite direction to v)

Jonathan

The old school engineering thread.

Peleus

TheAmateur wrote: »

Yep that's what I did alright!:o The exam qs seem pretty consistent through the two years, an even split between statics and dynamics and an even split between simple remember the formula qs and crazy abstract qs.
Did you do q. 9 in the 2007 exam by any chance? I got D in that one, just want to see if what I did was right (added the two momentums and divided by time because u was in the opposite direction to v)

ye thats what i got. I said F= rate of change in momentum. = (mv-mu)/t = 8000. but obviously either u or v will be negative (depending on how you look at it) so ye you add the two momentums in actual fact.

devinejay

Jonathan wrote: »

The old school engineering thread.

Weird!

Wrt to all the chatter on that old thread about part time jobs, does anyone else work here? I used to do 16 hours a week, now I'm down to 7 for my sanity but I wouldn't agree with people saying "Do you really want to take engineering seriously or do you want a few quid". I always figured that I were to put more work in to college it would be during the weekdays and not intrude with part time work. I can't really say much before the exams, it could all go really wrong, maybe I should be doing college work all the time!

Jonathan

devinejay wrote: »

Weird!

Wrt to all the chatter on that old thread about part time jobs, does anyone else work here? I used to do 16 hours a week, now I'm down to 7 for my sanity but I wouldn't agree with people saying "Do you really want to take engineering seriously or do you want a few quid". I always figured that I were to put more work in to college it would be during the weekdays and not intrude with part time work. I can't really say much before the exams, it could all go really wrong, maybe I should be doing college work all the time!

I dont work during the college year.

I work all summer and work the money down over the college year.

I've done that for the past two years and it has worked for me.

Peleus

i did that this year. but i spent all my money in the first term and spent the last two terms with no money. not good. Im gonna work all year next year, if i can get my job back

TheAmateur

How many handouts did we get from Dr. Kokaram? I've only three here, could've sworn there were more...

Peleus

You're better off than me. I only have two. One that starts with something called Run Length Encoding and the other one that starts off as an exam paper and ends with a few more questions.

Don't know what else he gave us. I missed/slept in a few of his lectures so i probably missed alot. Theres loads of stuff on his website sigmedia.tv

Brian

All of his stuff is on sigmedia, apparently.

devinejay

Yeah it's on sigmedia, but it's very badly organised you you might have trouble figuring out which was his first, second lecture etc. Also it's hard to get past all the pictures of him and his oscar.

TheAmateur

Was just wondering: Was there a point in taking our blue booklets after the mechanics exam? I mean it's not like anyone's gonna look at them or anything, the mcq sheet is all they need isn't it?
EDIT: Also, one of the maths demonstrators said he'd be surprised if there was integration on the test tomorrow but seeing as 1E1 is "defined" as chapters 1-6, I can't understand how there wouldn't be. Anyone hear anything more conclusive?

Peleus

devinejay wrote: »

Also it's hard to get past all the pictures of him and his oscar.

If you manage to avoid them on the website, there in the first set of notes.

TheAmateur wrote: »

Was just wondering: Was there a point in taking our blue booklets after the mechanics exam? I mean it's not like anyone's gonna look at them or anything, the mcq sheet is all they need isn't it?

ye the mcq is all they need. dont know why we handed up the blue yokes.

EDIT:

TheAmateur wrote: »

EDIT: Also, one of the maths demonstrators said he'd be surprised if there was integration on the test tomorrow but seeing as 1E1 is "defined" as chapters 1-6, I can't understand how there wouldn't be. Anyone hear anything more conclusive?

Im guessing there wont be. 1e1 will be like christmas and 1e2 like easter. so mostly differentiaition and limits and int value thm, definitions, functions etc..

Oh whats the continuous assesment for chemistry and electricity? I heard our physics and chemistry experiments count towards 1e4 and 1e6 and as well as 1e9. Is this true? Anyone know what percent of 1e4/1e6 they count for? if its true.

Jonathan

Peleus wrote: »

ye the mcq is all they need. dont know why we handed up the blue yokes.

If you fail, they will go through your roughwork to try to award marks.

Peleus

Jonathan wrote: »

If you fail, they will go through your roughwork to try to award marks.

ha good luck to them. my rough work was all over the place.

EDIT: i may have mumps.... ooo the suspense...