AC Power, Current Wars, the Thing, the Theremin

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Lecture 25 AC Power, Current Wars, The Thing, The Theremin

Friday, November 15, 13 Damped Oscillations: RLC circuits

Energy gradually dumped into resistor: i^2*R

Friday, November 15, 13 Alternating Current

For Example: in USA, V=120 V AC, 60 Hz

But Why Bother?

Friday, November 15, 13 2 reasons: Transformers and Power loss:

P=i^2R

Maintain low current and high voltage for transmission

Friday, November 15, 13 Current Wars

DC AC

Edison Westinghouse/ Tesla

Friday, November 15, 13 Edison's publicity campaign (from Wikipedia)

Edison carried out a campaign to discourage the use of alternating current, including spreading disinformation on fatal AC accidents, publicly killing animals, and lobbying against the use of AC in state legislatures. Edison directed his technicians, primarily Arthur Kennelly and Harold P. Brown, to preside over several AC-driven executions of animals, primarily stray cats and dogs but also unwanted cattle and horses. Acting on these directives, they were to demonstrate to the press that alternating current was more dangerous than Edison's system of direct current. He also tried to popularize the term for being electrocuted as being "Westinghoused". Years after DC had lost the "war of the currents," in 1902, his ﬁlm crew made a movie of the electrocution with high voltage AC, supervised by Edison employees, of Topsy, a Coney Island circus elephant who had recently killed a man.

Edison opposed capital punishment, but his desire to disparage the system of alternating current led to the invention of the electric chair. Harold P. Brown, who was at this time being secretly paid by Edison, constructed the ﬁrst electric chair for the state of New York in order to promote the idea that alternating current was deadlier than DC.

When the chair was ﬁrst used, on August 6, 1890, the technicians on hand misjudged the voltage needed to kill the condemned prisoner, William Kemmler. The ﬁrst jolt of electricity was not enough to kill Kemmler, and only left him badly injured. The procedure had to be repeated and a reporter on hand described it as "an awful spectacle, far worse than hanging." George Westinghouse commented: "They would have done better using an axe."

Friday, November 15, 13 Tesla on the other hand....

Radio, AC Power, ﬂorescence, ignition systems......

“We are like tenant farmers chopping down the fence around our house for fuel when we should be using Natures inexhaustible sources of energy — sun, wind and tide. ..

Friday, November 15, 13 Tesla on the other hand....

Radio, AC Power, ﬂorescence, ignition systems......

“There is no thing endowed with life—from man, who is enslaving the elements, to the nimblest creature—in all this world that does not sway in its turn. Whenever action is born from force, though it be inﬁnitesimal, the cosmic balance is upset and the universal motion results.”

Friday, November 15, 13 Phasor Notation:

• http://www.animations.physics.unsw.edu.au/jw/ AC.html • http://science.sbcc.edu/physics/ﬂash/optics/ phasors4.swf

Friday, November 15, 13 Diode

Current is allowed in one direction, but not the other

Friday, November 15, 13 Use Diodes to build “rectiﬁers”

Half wave:

Friday, November 15, 13 Full Wave:

Friday, November 15, 13 DC is then smoothed with “ﬁlters”

High pass ﬁlter

Friday, November 15, 13 DC is then smoothed with “ﬁlters”

Low pass ﬁlter

Friday, November 15, 13 Leon Theremin (1896-1993) Soviet Inventor/ KGB Espionage Engineer

• Theremin – the classic Theremin (1920) • Burglar alarm, or "Signalling Apparatus" which used the Theremin effect (1920s) • Electromechanical television – Nipkow disk with mirrors instead of slots (ca. 1925) • Terpsitone – platform that converts dance movements into tones (1932) • Theremin cello – an electronic cello with no strings and no bow, using a plastic fingerboard, a handle for volume and two knobs for sound shaping (ca. 1930)[32][33][34][35] • Keyboard theremin (ca. 1930), looking like a small piano, "with hornlike tones"[36] • Rhythmicon – world's first drum machine (1931) • The Buran eavesdropping device (1947 or earlier) • The Great Seal bug, also known as "The Thing" – one of the first passive covert listening devices; first used by the USSR for spying (1945 or earlier)

Friday, November 15, 13 “The Thing” or “Great Seal Bug”

Theremins device was implanted inside a carved wooden plaque of the US seal given to ambassador to Soviets as a gesture of friendship. Was discovered by British radio operator and reverse engineered by MI5. Later was presented at special UN meeting in response to the downing of the U2 spy plane

Friday, November 15, 13 Forced Oscillations in 3 Easy Pieces

• Resistive Load • Capacitive Load • Inductive Load

Friday, November 15, 13 Alternating Current

Purely Resistive Load:

•Phase angle (ϕ) = 0 •Current and Voltage are in phase

Friday, November 15, 13 Alternating Current Purely Capacitive Load:

•Phase angle (ϕ) =-90 •Voltage “lags” current

Friday, November 15, 13 Alternating Current Purely Inductive Load:

•Phase angle (ϕ) =+90 •Voltage “leads” current

Friday, November 15, 13 Type Resistance Phase of (i) V relation

R R 0 V=IR

0 C X = 1/ωC leads v by 90 V=IX C C

0 L X = ωL lags v by 90 V=IX L L

Friday, November 15, 13 Leon Theremin (1896-1993) Soviet Inventor/ KGB Espionage Engineer

Friday, November 15, 13 “The Thing” or “Great Seal Bug”

Theremins device was implanted inside a carved wooden plaque of the US seal given to ambassador to Soviets as a gesture of friendship. Was discovered by British radio operator and reverse engineered by MI5. Later was presented as special UN meeting in response to the downing of the U2 spy plane

Friday, November 15, 13 Meissner Effect

Friday, November 15, 13 Pulsars -Highly magnetized remnant of supernova explosion -B-ﬁeld inclined with respect to angular motion

As star rotates, B ﬁeld sweeps radiation past our line of sight-> lighthouse effect Friday, November 15, 13 Jocelyn Bell-Discovery:1967

Dubbed: LGM-1

Friday, November 15, 13