A multimeter can be used to measure resistance in ohms. It can also be used to measure voltage, current, and other electrical characteristics.

The ohm (symbol: Ω) is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm.

Definition[link]

Several resistors. Their resistance, in ohms, is marked using a color code.

The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere, the conductor not being the seat of any electromotive force.^[1]

Failed to parse (Missing texvc executable; please see math/README to configure.): \Omega = \dfrac{\mbox{V}}{\mbox{A}} = \dfrac{\mbox{m}^2 \cdot \mbox{kg}}{\mbox{s} \cdot \mbox{C}^2} = \dfrac{\mbox{J}}{\mbox{s} \cdot \mbox{A}^2}=\dfrac{\mbox{kg}\cdot\mbox{m}^2}{\mbox{s}^3 \cdot \mbox{A}^2}= \dfrac{\mbox{J} \cdot \mbox{s}}{\mbox{C}^2} = \dfrac{\mbox{1}}{\mbox{S}}

V=volt, A=ampere, m=meter, kg=kilogram, s=second, C=coulomb, J=joule, S=siemen

In many cases the resistance of a conductor in ohms is approximately constant within a certain range of voltages, temperatures, and other parameters; one speaks of linear resistors. In other cases resistance varies (e.g., thermistors).

Commonly used multiples and submultiples in electrical and electronic usage are the milliohm, ohm, kilohm, megohm, and gigaohm.^[2]

In alternating current circuits, electrical impedance is also measured in ohms.

Conversions[link]

The siemens (symbol: S) is the SI derived unit of electric conductance and admittance, also known as the mho (ohm spelled backwards, symbol is ℧); it is the reciprocal of resistance in ohms.

Power as a function of resistance[link]

The power dissipated by a linear resistor may be calculated from its resistance, and voltage or current. The formula is a combination of Ohm's law and Joule's laws:

Failed to parse (Missing texvc executable; please see math/README to configure.): P=V\cdot I =\frac{V^2}{R} = I^2\cdot R

where P is the power in watts, R the resistance in ohms, V the voltage across the resistor, and I the current through it.

This formula is applicable to devices whose resistance varies with current.

Ohm symbol[link]

When preparing electronic documents, some document editing software will attempt to use the Symbol typeface to render the Ω character. Where the font is not supported, a W is displayed instead ("10 W" instead of "10 Ω", for instance). As W represents the watt, the SI unit of power, not resistance, this can lead to confusion.

An "R" can be used instead of the Ω symbol if it is not supported, thus, a 10 Ω resistor can also be represented as 10R. This is the British standard BS 1852 code. It is used in many instances where the value has a decimal place i.e. 5.6 Ω would be listed as 5R6. One advantage of this method is that it is relatively easy to "rub off" a decimal point symbol ".", changing the apparent value, compared to the "R" symbol, which would require more effort.

Unicode encodes the symbol as U+2126 Ω ohm sign, distinct from Greek omega among letterlike symbols, but it is only included for backwards compatibility and the Greek uppercase omega character U+03A9 Ω greek capital letter omega (HTML: Ω Ω) is preferred.^[3] In DOS and Windows, the alt code ALT 234 may produce the Ω symbol.

See also[link]

• Abohm
• Ohm's law
• Resistor
• Resistivity

References[link]

1. ^ BIPM SI Brochure: Appendix 1, p. 144
2. ^ The NIST Guide to the SI: 9.3 Spelling unit names with prefixes reports that IEEE/ASTM SI 10-2002 IEEE/ASTM Standard for Use of the International System of Units (SI): The Modern Metric System states that there are three cases in which the final vowel of an SI prefix is commonly omitted: megohm, kilohm, and hectare. "In all other cases in which the unit name begins with a vowel, both the final vowel of the prefix and the vowel of the unit name are retained and both are pronounced."
3. ^ Excerpts from The Unicode Standard, Version 4.0, accessed 11 October 2006

External links[link]

• Scanned books of Georg Simon Ohm at the library of the University of Applied Sciences Nuernberg
• Official SI brochure
• NIST Special Publication 811
• History of the ohm at sizes.com

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Chris Poland (born December 1, 1957) is an American guitarist, best known for being a former member of heavy metal band Megadeth.

Biography[link]

Early career[link]

Poland began playing the guitar in high school in Dunkirk, New York. He later replaced a former guitar instructor, Dick "Max" Maxfield, in the Cambridge, NY based rock/jazz band Welkin. He moved to Los Angeles in 1977, where from 1977 to 1982 he was the lead guitarist in the New Yorkers, a Jazz/Rock fusion band, with Robert Pagliari on fretless bass, Gar Samuelson on drums, Stu Samuelson on guitar, and Don Roper on saxophone. He says that he learnt timing playing with Gar and also that playing with him made him a better player.

Megadeth[link]

In 1984, Poland's bandmate from the New Yorkers, Gar Samuelson, became the drummer of thrash metal band Megadeth. Megadeth had been formed the previous year by Dave Mustaine, the original lead guitarist of fellow thrash metal band Metallica, who had been fired from the band because of his substance abuse. After seeing Samuelson perform live with Megadeth, Poland went backstage and suggested an impromptu audition as a lead guitarist. Poland thereafter became a full member of the band, along with Samuelson, Mustaine, and bass player David Ellefson.

In 1985, Megadeth released their first album Killing Is My Business... And Business Is Good!, which showcased Poland's dynamic style of playing. However, he was arrested by Police for trying to score heroin, Poland left the band during the tour to support the album, and was replaced temporarily by guitarist Mike Albert. Poland later rejoined the band to record their second album Peace Sells... But Who's Buying? in 1986. The album was highly acclaimed critically for both its instrumental and lyrical complexity, and is today considered widely to be one of the defining records of thrash metal. Allmusic referred to Peace Sells... but Who's Buying? as "One of the most influential metal albums of its decade, and certainly one of the few truly definitive thrash albums".^[1]

Mustaine later referred to Poland as "an amazing guitar player—he can play circles around me".^[2] However, Poland and Samuelson's relations with Mustaine and Ellefson worsened, due in part to the former's increasing drug dependencies which led to the pair pawning the band's equipment to fund their drug habits.

In July 1987, a conflict arose between Mustaine and Poland regarding a t-shirt contract that Poland claimed to have been left out of. Poland quit the band in protest leading to an ongoing feud between the two musicians. For Megadeth's third album So Far, So Good... So What! Mustaine wrote a song called "Liar" about Poland's drug use and lifestyle. Mustaine would regularly dedicate it to Poland during live performances.

Post-Megadeth[link]

After leaving Megadeth, Poland was treated successfully for substance abuse, and joined punk rock legends The Circle Jerks as a bass player. In 1990, he released Return to Metalopolis a solo heavy metal/jazz fusion album. Shortly beforehand, he agreed to record demos for Megadeth's fourth album, Rust in Peace, but declined what would be the first of two offers to re-join the band permanently (in this instance partly because of his concentration on his solo album, and the fact that, since most of the album's music and arrangements had already been written, Poland felt that the scope for his input would be limited). Guitarist Marty Friedman joined Megadeth later that year, and adapted some of Poland's guitar solos for the release version of Rust in Peace, which would go on to be one of Megadeth's most critically praised albums.

In the mid to late 1990s, Poland worked on other collaborative musical projects, including the progressive rock band Damn the Machine, with David Randi on bass, and Dave Clemmons as vocalist and co-guitarist. In 1993, the band released their eponymous debut album (on A and M Records), with strongly political lyrical content. They also released a promotional record, Silence, featuring covers of "I'd Love to Change the World" by blues-rock band Ten Years After, and "Cat Food" by progressive rock/jazz fusion band King Crimson.

Upon Dave Clemmons' departure from the band, the remaining members recruited a new vocalist, John Skipp, and re-formed as Mumbo's Brain, recording Excerpts From The Book Of Mumbo in 1995. The band disbanded following the departures of David Randi, and John Skipp.

2000s[link]

In 2000, ten years after the release of Return to Metalopolis, Poland released his second solo album, Chasing the Sun, as well as a solo compilation album Rare Trax. In 2007, he released Return to Metalopolis - Live, featuring a live performance of the titular album.

Poland is currently a member of the primarily jazz fusion band OHM, formed in 2002, with Poland on guitar, Kofi Baker on drums and Robertino Pagliari on bass guitar. They released their self-titled debut album in 2003, followed by Amino Acid Flashback in 2005, and Circus of Sound in 2008. The band also released a live album in 2004, and a DVD, Live at the New Brookland Tavern, in 2006.

In 2003, Poland performed a solo on Purified from the Lamb of God album As The Palaces Burn. The following year, he contributed to Lamb of God's next album, Ashes of the Wake, with a guitar solo on the album's instrumental title-track (beginning at 3:45 and ending at 4:15).

In a surprise turn in 2004, Dave Mustaine requested Poland to record guitar solos for the Megadeth record The System Has Failed, the first Megadeth album not to feature original bass player and founding member David Ellefson. Poland recorded the solos on a contractual basis, but did not re-join the band. Poland and Mustaine subsequently came into dispute with one another over payments relating to the album, however, they appear to have made amends once more as Poland began posting on the official Megadeth online message board.

In 2008, Poland appeared on Misty Mountain Hop: A Millennium Tribute to Led Zeppelin by heavy metal/hard rock band Harry Slash & The Slashtones. The following year, he recorded a track for the compilation record Guitars That Ate My Brain (which also includes a track by Guns N' Roses' guitarist Bumblefoot).

In 2009, Poland formed OHMphrey, a side-project with Robby Pagliari of OHM, and Jake Cinninger, Kris Myers, and Joel Cummins of progressive rock band Umphrey's McGee. OHMphrey's debut album, OHMphrey, was released through Magna Carta Records on May 19, 2009.

Playing style[link]

Poland has a severed tendon on the index finger on his fret hand, which allows him to stretch unusually far with his finger.^{[citation needed]} He has partially attributed the greater flexibility that this affords him to the evolution of his signature guitar playing style, defined by smoothly phrased passages and wide intervallic leaps.

Discography[link]

Solo albums[link]

• 1990: Return to Metalopolis
• 2000: Chasing the Sun
• 2000: Rare Trax (compilation)
• 2007: Return to Metalopolis Live (live)

With Megadeth[link]

• 1985: Killing Is My Business... and Business Is Good!
• 1986: Peace Sells... But Who's Buying?
• 1990: Rust in Peace (Poland's solos appear on the demo recordings of "Holy Wars... The Punishment Due", "Take No Prisoners", and "Rust in Peace... Polaris", which were released as bonus tracks on the 2004 remaster)
• 2000: Capitol Punishment: The Megadeth Years (compilation)
• 2004: The System Has Failed
• 2005: Greatest Hits: Back to the Start (compilation)
• 2007: Warchest (compilation)
• 2008: Anthology: Set the World Afire (compilation)

With Damn the Machine[link]

• 1993: Damn the Machine

With Mumbo's Brain[link]

• 1995: Excerpts From The Book Of Mumbo

With Lamb of God[link]

• 2003: As the Palaces Burn
• 2004: Ashes of the Wake

With OHM[link]

• 2003: OHM
• 2004: "Live" On KPFK 90.7 FM
• 2005: Amino Acid Flashback
• 2006: Live at the New Brookland Tavern (DVD)
• 2008: Circus of Sound

With OHMphrey[link]

• 2009: OHMphrey
• 2012: Posthaste

With Polcat

• 2012: Polcat

Other album appearances[link]

• 2009: Guitars That Ate My Brain
• 2009: Misty Mountain Hop: A Millennium Tribute to Led Zeppelin
• 2012: Plains of Oblivion - Jeff Loomis

[edit] Equipment^[3]

Guitars[link]

• Yamaha SBG 2000 x 3 (2 Hollow Body)
• Yamaha AES 800
• Yamaha SG2200
• Paul Reed Smith Custom 24 during the Return To Metalopolis and early Damn The Machine eras
• B.C. Rich Custom Eagle (pre-Megadeth)
• B.C. Rich Warlock
• B.C. Rich Bich
• B.C. Rich STiii
• Jackson Randy Rhoads

Amplifiers[link]

• Bogner Fish Pre Amp
• Mosvalve 500 x 4
• Mesa/Boogie 395
• Mesa/Boogie Strategy 400
• Demeter Inverter
• Eminence Speakers
• Carvin Steve Vai 2x12 cabinets
• Earcandy Buzzbomb 2x12 cabinets

References[link]

External links[link]

• Official website
• 2006 Chris Poland Interview - by Brian D. Holland
• Tone Center Records, OHM's record company