Engineering Thread

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.

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

password: boardsie


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

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.

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 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.