Electric circuit. Use of ammeters and voltmeters
Fig. 35.3 illustrates some of the symbols used in electric circuit diagrams. When the terminals of a cell are joined to the ends of a resistor an electric circuit is formed. If several resistors are connected end to end in the circuit so as to form a
continuous path they are said to be in series and the same current flows through each. The current may be measured with an ammeter which is placed in series with the resistors (Fig. 35.4). An ammeter has a low resistance, so that it introduces as little extra resistance as possible into the circuit.
A voltmeter is used to measure the potential difference between the ends of a
resistor, and is therefore connected across (i.e., in parallel with) the resistor. Voltmeters have a high resistance, and the current they take is usually negligible. The construction and action of ammeters and voltmeters is dealt with in chapter