Voltage and current

Electric voltage across a part of a circuit tells us how much work is done for each coulomb of charge moved through that part, that is, the ratio of the work to the charge: U = A/q, so A = qU and q = A/U. Its unit is the volt (V): 1 V = 1 J/C, that is, when 1 C passes at a voltage of 1 V, 1 J of work is done. Smaller and larger units: 1 mV = 10⁻³ V, 1 kV = 10³ V. A dry cell gives about 1.5 V, a car accumulator 12 V; the 220 V mains of a home is extremely dangerous, and no measuring or experiments are done on it. Voltage is measured by a voltmeter, which is connected in parallel to the part being measured (the poles of the source or the ends of a consumer), with its “+” terminal towards the positive pole of the source. When several galvanic cells are connected one after another, their voltages add up.