“lost volts” when a cell is producing current in a circuit

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“lost volts” when a cell is producing current in a circuit For practical purposes, the e.m.f. of a cell may be measured to a very close approximation by taking the reading of a high-resistance voltmeter connected directly across the cell terminals when the cell is not connected to anything else. The reason why this value is only approximate […]

Arrangement of cells

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Arrangement of cells A group of cells connected together is called a battery. Normally, cells are connected in series, the positive of one being connected to the negative of the next and so on (Fig. 35.7). On occasions, however, they may be connected in parallel, i.e., all the positives connected together and the same with the negatives […]

Practical importance of the internal resistance of a cell

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Practical importance of the internal resistance of a cell Cells of one particular kind, for example, dry cells, may be obtained in several different sizes, but so long as they are all made of exactly the same materials and have the same strength of electrolyte they will have identical e.m.f.s. The strength of the current which is […]

Resistors in parallel

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Resistors in parallel Resistors are said to be in parallel when they are placed side by side and their corresponding ends joined together (Fig. 35.6). The same potential difference will thus be applied to each, but they will share the main current in the circuit. We will suppose that the main current I divides into II, 12, and […]

Resistors in series

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Resistors in series A number of resistors R), R2′ R3′ in ohms, are said to be connected in series if they are connected end to end consecutively so that the same current I, in amperes, flows through each (Fig. 35.5). If R is the combined resistance and V, in volts, is the total potential difference across the resistors, […]

Resistors

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Resistors Radio and television receivers contain large numbers of resistors with resistances of anything from a few ohms to millions of ohms. Some are wire wound, while others are made from carbon or graphite. They are supplied with either wire ends or terminals for connection purposes. The special standard resistors designed for laboratory purposes are described in chapter 40.

Effect of temperature on resistance. Semiconductors

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Effect of temperature on resistance. Semiconductors The resistance of a pure metal increases with temperature but the resistance of certain other conducting materials, e.g., carbon decreases with temperature. Various metal alloys, notably manganin and constantan which are used for making standard resistors, show very small resistance changes with temperature under normal laboratory conditions. Certain other substances notably germanium, silicon, and […]