Voltage and current

Current tells us how much charge passes through a cross-section of a conductor every second, that is, the ratio of the charge to the time: I = q/t, so q = I·t. Its unit is the ampere (A): 1 A = 1 C/1 s, that is, if 1 C passes through the cross-section in 1 s the current is 1 A. In practice the milliampere (1 mA = 10⁻³ A) and the microampere (1 µA = 10⁻⁶ A) are used. Current is a scalar quantity; the word “force” in its name has nothing to do with force in mechanics. Current is measured with an ammeter, which is connected in series with the consumer, with its “+” terminal joined to the wire coming from the positive pole of the source. In a series circuit the current is the same everywhere, so the ammeter shows the same value whether it is placed before or after the consumer. Remember to convert minutes to seconds.