Основы английского языка для судовых электриков - страница 27
45. /15 мин./ Ознакомьтесь со смыслом следующих 4 предложений. Прочтите следующий за ними текст, стремясь глубже понять его содержание. Отметьте буквой R истинные, а буквой W ложные утверждения.
1. Kirchhoff’s voltage law states that the sum of all voltages around a closed path in an electrical system is zero. 2. It is not quite natural to use a plus sign for a voltage rise & a minus sign for a voltage fall or drop. 3. Potential difference between two points is defined as the work done on a unit positive charge, while it is being removed from these two points. 4. The unit.positive charge has been given energy in the amount of E volts during its passage through the battery.
Kirchhoff’s Voltage Law
Kirchhoff’s voltage law states that the sum of all voltages/potential difference/ around a closed path in an electrical system is zero. In Fig.5 you can show part of an electrical network containing two sources of voltage /a battery & a generator/ & three currents with assumed positive directions. The voltage arrow in the circle Will signify voltage rise in the direction of the arrow.
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| Fig. 5. A network to illustrate Kirchhoffs. |
It is quite natural to use a plus sign for a voltage rise & a minus sign for a voltage fall or drop. There is a voltage drop from a to b which can be represented as I R, employing Ohm’s law. From b to c there is a voltage rise that will be represented in the equation as +E>2 The current is represented by an arrow. Hence I>3 is drawn in the direction of the arrow for E>2. We assume zero internal resistance in the battery & the source E>2 as well as in the wires that connect them into the circuit at points h, a, b, & c.
The following two voltage equations are written as examples of the application of Kirchhoff’s law of voltage to the loops indicated E, = IjR, + I>2R>2, E, + E = I.R, + I>3R>3.
An extremely important & basic principle is applied here, & it is the fundamental reason that Kirchhoff’s voltage law is true. This principle is no more than an application of the law of conservation of energy. Potential difference between."two points is defined as the work done on a unit positive charge, \yhile it is being moved from one of the points to the other one. If %e imagine a unit positive charge starting at the negative terminal of the battery & moving through it to the positive terminal, work will have to be done on the charge because it must be moved against the electrical field inside the battery. It is a fact that the streamlines of the field pass inside the battery from plus to minus & that the field exerts a force on the positive charge opposing its motion inside from minus to plus. So the unit positive charge has been given energy in the amount of. E volts, by chemical action, during its passage through the battery. Then, in passing on through the zero-resistance wire to point a through R, & R>2 to g & back through the zero-resistance wire to hand them to its starting point at the negative terminal, it goes'in the same.direction as the field streamlines. During this part of its journey it gives up the energy it received in the battery, in a fashion similar to the giving up of energy by a rock that is allowed to fall to the earth after its energy has been increased by lifting it a distance above the earth’s surface.
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13-1. Его собственный опыт, например, представляет большой интерес. 2. В некоторых случаях обе полосы расположены близко друг к другу. 3. Эту идею следует принять к сведению. 4. Способность некоторых веществ притягиваться друг к другу почти наверняка объясняется магнитными причинами.
16 - КТермометр показывает температуру пара в блоке. 2. Брошюра в 30 страниц по этому вопросу была опубликована в прошлом месяце. 3. У металлов группы железа плотность уровней примерно такая же, как у меди. 4. Независимо от того, какой применяется метод обработки смесью.
18-1. Мы вынуждены будем ввести в эту цепь реле, управляемое током. 2. Сопротивление току остается постоянным. %■ Современные направления вполне возможно приведут к производству вычислительных машин небольших размеров.
