ohmn.²

Brit.

/əʊm/, U.S.

/oʊm/

Forms: 1800s ohma, 1800s– ohm.

Origin: From a proper name. Etymon: proper name Ohm.

Etymology: < the name of Georg Simon Ohm (1787–1854), German physicist, who determined mathematically the law of the flow of electricity (see Ohm's law n. 1).With form ohma in quot. 1861 at main sense compare -a suffix¹ 1.

A unit of electrical resistance (also used for reactance and impedance, and incorporated in the International System of Units), defined as the resistance that exists between two points when a potential difference between them of one volt produces a current of one ampere. Symbol Ω.The word ohma was originally proposed for the practical unit of ‘tension’ (voltage), along with volt for the unit of resistance (see quot. 1861, which also appears in Electrician (1861) 9 Nov. 4 and is from the paper read at the Sept. 1861 meeting of the British Association for the Advancement of Science). The origin of the change in application of the word has not been traced in print. See also ohmad n.In 1893, at the International Electrical Congress, a further definition of the ohm (the international ohm) was established. It was defined as the resistance of a 106.3 cm long column of mercury of constant cross-sectional area, with a mass of 14.4521 grams, held at a temperature of zero degrees Celsius. At the 1948 General Conference on Weights and Measures, the use of the international ohm was abandoned and the ohm was redefined in terms of the absolute ampere.

ΘΚΠ

the world > matter > physics > electromagnetic radiation > electricity > resistance > [noun] > unit of resistance

ohm1861

ohmad1865

ohm-centimetre1920

ohm-metre1935

milliohm1939

abohm1940

1861 L. Clark & C. Bright in L. Clark Exper. Investig. Laws Propagation Electr. Current 49 Let us derive terms from the names of some of our most eminent philosophers... We shall then have the following table: A.—Tension. 1 Daniell's Element = 1 Ohma, or unit of tension... B.—Quantity. 1 Ohma, by 1 metre square at 1 milliometre [sic] distance = 1 Farad, or unit of quantity... D.—Resistance. 1 Farad per second = 1 Volt, or unit of resistance.

1867 W. H. Preece in London, Edinb., & Dublin Philos. Mag. 4th Ser. 33 397 I beg to suggest..to those physicists and electricians who have adopted the British-Association unit for electrical measurements, that in place of expressing this unit, as is variously done at present, by B.A. unit, Ohmad, Ohm, 10⁷ metre/second, &c., it would be very convenient to adopt some universal symbol analogous to that used for degrees (°). The Greek letter ω appears to me very convenient.

1889 Nature 14 Feb. 368/2 At the Congress of Electricians in Paris in 1881, the Ohm was unanimously adopted as an international standard.

1894 Proc. Internat. Electr. Congr. Chicago 1893 17 As a unit of resistance, the international ohm,..is represented by the resistance offered to an unvarying electric current by a column of mercury at the temperature of melting ice, 14,4521 grammes in mass of a constant cross-sectional area and of a length of 106.3 centimetres.

1943 F. E. Terman Radio Engineers' Handbk. ii. 40 Wire-wound variable resistors of these types are available up to about 100,000 ohms, and are capable of dissipating up to about 15 watts.

1973 D. Aldous in Pye Bk. Audio vii. 75/2 Most transistor amplifiers offer a wide range of output impedances, usually from 4 to 16 ohms.

1994 Gramophone July 143/2 Using advanced ‘full-size’ diaphragms with neodymium magnets, the headphones have an 85 ohms impedance.

Compounds

ohm-ammeter n. rare an instrument for measuring electrical current and resistance, a combination of an ammeter and an ohmmeter.Apparently only attested in dictionaries or glossaries.

ΚΠ

1902 N.E.D. at Ohm² Ohm-ammeter.

ohm-centimetre n. the unit of electrical resistivity in the cgs system, equal to 0.01 ohm-metre.

ΘΚΠ

the world > matter > physics > electromagnetic radiation > electricity > resistance > [noun] > unit of resistance

ohm1861

ohmad1865

ohm-centimetre1920

ohm-metre1935

milliohm1939

abohm1940

1920 W. T. Maccall Continuous Current Electr. Engin. (ed. 2) iii. 18 The resistance of a conductor 1 cm. long and 1 sq. cm. cross-section..is called the specific resistance per centimetre cube... A better name is ohm-centimetre (or microhm-cm.).

1957 H. Cotton Electr. Technol. (ed. 7) iii. 67 It is..logical to express ρ as so many ohms-centimetre..or ohm-metre [sic]... For example, for copper at normal room temperature ρ = 1·72 × 10⁻⁶ Ω-cm.

1974 Encycl. Brit. Micropædia VIII. 524/1 The resistivity of an exceedingly good electrical conductor, such as hard-drawn copper, at 20° C (68° F) is 1·77 × 10⁻⁸ ohm-metre, 1·77 × 10⁻⁶ ohm-centimetre, or 10·7 ohm-circular mils per foot.

ohm-metre n. the unit of electrical resistivity in the International System of Units, being the resistivity of a substance of which a metre cube has a resistance of 1 ohm.

ΘΚΠ

the world > matter > physics > electromagnetic radiation > electricity > resistance > [noun] > unit of resistance

ohm1861

ohmad1865

ohm-centimetre1920

ohm-metre1935

milliohm1939

abohm1940

1935 Proc. National Acad. Sci. U.S.A. 21 582 The following table contains an incomplete list of m.k.s. units:... Resistivity..ρ..ohm.meter.

1975 G. Anderson Coring vii. 121 The porosity of the sand is above 20% and the resistivity ranges from 0.3 ohm-m for saltwater sands to several ohm-meters for oil-saturated sands.

This entry has been updated (OED Third Edition, March 2004; most recently modified version published online June 2022).

单词	ohm
释义	† ohmn.¹ Forms: 1600s ome, 1800s ohm. Origin: A borrowing from German. Etymon: German Ohm. Etymology: < German Ohm (see aum n.). N.E.D. (1902) gives the pronunciation as (ōm) /oːm/. Obsolete. A liquid measure formerly used in Germany, varying locally between 30 and 36 gallons (approx. 137 to 164 litres). Cf. aum n. ΘΚΠ the world > relative properties > measurement > the scientific measurement of volume > measure(s) of capacity > [noun] > liquid measure of capacity > specific units of liquid measure > German units strif1495 ohm1851 1611 T. Coryate Crudities sig. Oo This huge vessel..containeth a hundred and two and thirty fuders, three omes, and as many firtles. These are peculiar names for certaine German measures... The ome is a measure whereof sixe do make a fuder. 1851 H. W. Longfellow Golden Legend iv. 169 It comes from Bacharach on the Rhine..And costs some hundred florins the ohm [rhyme Rome]. This entry has been updated (OED Third Edition, March 2004; most recently modified version published online December 2020). ohmn.² Brit. /əʊm/, U.S. /oʊm/ Forms: 1800s ohma, 1800s– ohm. Origin: From a proper name. Etymon: proper name Ohm. Etymology: < the name of Georg Simon Ohm (1787–1854), German physicist, who determined mathematically the law of the flow of electricity (see Ohm's law n. 1).With form ohma in quot. 1861 at main sense compare -a suffix¹ 1. A unit of electrical resistance (also used for reactance and impedance, and incorporated in the International System of Units), defined as the resistance that exists between two points when a potential difference between them of one volt produces a current of one ampere. Symbol Ω.The word ohma was originally proposed for the practical unit of ‘tension’ (voltage), along with volt for the unit of resistance (see quot. 1861, which also appears in Electrician (1861) 9 Nov. 4 and is from the paper read at the Sept. 1861 meeting of the British Association for the Advancement of Science). The origin of the change in application of the word has not been traced in print. See also ohmad n.In 1893, at the International Electrical Congress, a further definition of the ohm (the international ohm) was established. It was defined as the resistance of a 106.3 cm long column of mercury of constant cross-sectional area, with a mass of 14.4521 grams, held at a temperature of zero degrees Celsius. At the 1948 General Conference on Weights and Measures, the use of the international ohm was abandoned and the ohm was redefined in terms of the absolute ampere. ΘΚΠ the world > matter > physics > electromagnetic radiation > electricity > resistance > [noun] > unit of resistance ohm1861 ohmad1865 ohm-centimetre1920 ohm-metre1935 milliohm1939 abohm1940 1861 L. Clark & C. Bright in L. Clark Exper. Investig. Laws Propagation Electr. Current 49 Let us derive terms from the names of some of our most eminent philosophers... We shall then have the following table: A.—Tension. 1 Daniell's Element = 1 Ohma, or unit of tension... B.—Quantity. 1 Ohma, by 1 metre square at 1 milliometre [sic] distance = 1 Farad, or unit of quantity... D.—Resistance. 1 Farad per second = 1 Volt, or unit of resistance. 1867 W. H. Preece in London, Edinb., & Dublin Philos. Mag. 4th Ser. 33 397 I beg to suggest..to those physicists and electricians who have adopted the British-Association unit for electrical measurements, that in place of expressing this unit, as is variously done at present, by B.A. unit, Ohmad, Ohm, 10⁷ metre/second, &c., it would be very convenient to adopt some universal symbol analogous to that used for degrees (°). The Greek letter ω appears to me very convenient. 1889 Nature 14 Feb. 368/2 At the Congress of Electricians in Paris in 1881, the Ohm was unanimously adopted as an international standard. 1894 Proc. Internat. Electr. Congr. Chicago 1893 17 As a unit of resistance, the international ohm,..is represented by the resistance offered to an unvarying electric current by a column of mercury at the temperature of melting ice, 14,4521 grammes in mass of a constant cross-sectional area and of a length of 106.3 centimetres. 1943 F. E. Terman Radio Engineers' Handbk. ii. 40 Wire-wound variable resistors of these types are available up to about 100,000 ohms, and are capable of dissipating up to about 15 watts. 1973 D. Aldous in Pye Bk. Audio vii. 75/2 Most transistor amplifiers offer a wide range of output impedances, usually from 4 to 16 ohms. 1994 Gramophone July 143/2 Using advanced ‘full-size’ diaphragms with neodymium magnets, the headphones have an 85 ohms impedance. Compounds ohm-ammeter n. rare an instrument for measuring electrical current and resistance, a combination of an ammeter and an ohmmeter.Apparently only attested in dictionaries or glossaries. ΚΠ 1902 N.E.D. at Ohm² Ohm-ammeter. ohm-centimetre n. the unit of electrical resistivity in the cgs system, equal to 0.01 ohm-metre. ΘΚΠ the world > matter > physics > electromagnetic radiation > electricity > resistance > [noun] > unit of resistance ohm1861 ohmad1865 ohm-centimetre1920 ohm-metre1935 milliohm1939 abohm1940 1920 W. T. Maccall Continuous Current Electr. Engin. (ed. 2) iii. 18 The resistance of a conductor 1 cm. long and 1 sq. cm. cross-section..is called the specific resistance per centimetre cube... A better name is ohm-centimetre (or microhm-cm.). 1957 H. Cotton Electr. Technol. (ed. 7) iii. 67 It is..logical to express ρ as so many ohms-centimetre..or ohm-metre [sic]... For example, for copper at normal room temperature ρ = 1·72 × 10⁻⁶ Ω-cm. 1974 Encycl. Brit. Micropædia VIII. 524/1 The resistivity of an exceedingly good electrical conductor, such as hard-drawn copper, at 20° C (68° F) is 1·77 × 10⁻⁸ ohm-metre, 1·77 × 10⁻⁶ ohm-centimetre, or 10·7 ohm-circular mils per foot. ohm-metre n. the unit of electrical resistivity in the International System of Units, being the resistivity of a substance of which a metre cube has a resistance of 1 ohm. ΘΚΠ the world > matter > physics > electromagnetic radiation > electricity > resistance > [noun] > unit of resistance ohm1861 ohmad1865 ohm-centimetre1920 ohm-metre1935 milliohm1939 abohm1940 1935 Proc. National Acad. Sci. U.S.A. 21 582 The following table contains an incomplete list of m.k.s. units:... Resistivity..ρ..ohm.meter. 1957 H. Cotton Electr. Technol. (ed. 7) iii. 67 It is..logical to express ρ as so many ohms-centimetre..or ohm-metre [sic]... For example, for copper at normal room temperature ρ..= 1·72 × 10⁻⁸ Ω-m. 1975 G. Anderson Coring vii. 121 The porosity of the sand is above 20% and the resistivity ranges from 0.3 ohm-m for saltwater sands to several ohm-meters for oil-saturated sands. This entry has been updated (OED Third Edition, March 2004; most recently modified version published online June 2022). < n.¹1611n.²1861
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† ohmn.1

ohmn.2

Compounds

† ohmn.¹

ohmn.²