| 释义 |
farad Electr.|ˈfærəd|
[short f. Faraday.]
1. a. Suggested (but apparently not used) as a name for a unit of charge, equal to approximately 9·5 × 10-10 coulomb.
The unit was defined as the charge on either plate of a capacitor that has plates one square metre in area spaced one millimetre apart and charged to the voltage of a Daniell cell, there being dry air between the plates.
1861Clark & Bright in Electrician 9 Nov. 4/2 The farad, or unit of quantity, is as small a one as is likely to be required in practice... One hundred farad, if allowed to pass through a very sensitive galvanometer, produce a visible motion of the needle.
b. A unit of charge (equal to the present microcoulomb) and also of capacitance (equal to the present microfarad). Disused.
1868Rep. Brit. Assoc. 1867 488, 105 EMF, acting on a circuit of 1013, will pass in one second 10-8 absolute units of quantity; and similarly, 105 EMF will charge a condenser of absolute capacity equal to 10-13 absolute units with 10-8 absolute units of quantity... Mr. Clark calls the unit of quantity thus defined (10-8) one Farad, and similarly says that the unit of capacity has a capacity of one Farad, it being understood that this is the capacity when charged with unit electromotive force (105). 1868L. Clark Elem. Treat. Electr. Measurement vii. 44 The farad is that quantity of electricity which, with an electromotive force of one volt, would flow through a resistance of one megohm in one second. 1875J. T. Sprague Electricity v. 156 Microfarad = Microveber/Volt = 10-8/105 = 10-13. The microfarad here represents what is usually called the farad.
2. The practical unit of capacitance (now incorporated into the International System of Units), being the capacitance of a capacitor in which a charge of one coulomb raises the potential difference between the plates by one volt. (Orig. also used as a unit of charge, equal to the present coulomb.)
1873J. C. Maxwell Electr. & Magn. II. iv. x. 244 The quantity of electricity which flows through one Ohm under the electromotive force of one Volt during one second, is equal to the charge produced in a condenser whose capacity is one Farad by an electromotive force of one Volt. 1874Phil. Trans. R. Soc. CLXIV. 1 Certain multiples have been adopted in practice and have received names, and are now in almost universal use among electricians. These units are:..Capacity.—The Farad, equal to 10-7 absolute electromagnetic units. Ibid. 2 The measure of quantity is the same as that of electrostatic capacity, and in practice generally receives the same name, although it has been sometimes called the ‘Weber’; the weber or farad quantity is equal to 10-2 absolute units. Electrical currents are defined as currents of so many farads per second. 1881Electrician 24 Sept. 297/2 At the meeting [of the Paris Electrical Congress] the report of the First Section on Electrical Units was received, and the following resolutions adopted:—..7. The name farad will be given to the capacity defined by the condition that a coulomb in a farad gives a volt. 1881Maxwell Electr. & Magn. II. 246 The practical unit of capacity is called the Farad. 1882Electrician 15 July 205/2 The unit of static quantity is a farad, or that quantity which, if discharged through one ohm in one second, would give a veber current. 1892Gloss. Electrical Terms in Lightning 3 Mar. Supp. 7 The Farad is the capacity of a conductor in which the electrical pressure is raised one volt by the addition of one coulomb. 1894Rep. Brit. Assoc. 1894 122 Governments represented by the delegates of this International Congress of Electricians..are..recommended to formally adopt as legal units of electrical measure the following... As a unit of capacity the international farad, which is the capacity of a condenser charged to a potential of one international volt by one international coulomb of electricity. 1925Bryant & Correll Alternating-Current Circuits ii. 51 The farad is too large a unit for most considerations, and the microfarad is more common, there being 1,000,000 microfarads in 1 farad. 1947Jrnl. Inst. Electr. Engineers XCIV. i. 342/1 From the 1st January, 1948, the units employed will be those derived from the centimetre, gramme and second, i.e. the so-called ‘absolute’ units... One international farad = 0·99951 ‘absolute’ farad. 1958W. C. Michels in Condon & Odishaw Handbk. Physics iv. v. 55/1 Precision standards are readily available in decade values from 10-3 ohm to 106 ohms, from 10-10 farad to 10-5 farad, and from 10-4 henry to 10 henrys. |