DC and AC volatage and current Preparing and measuring. Presented by Kamil Wojnarowski and Sebastian Białecki February 2012

U is the symbol of voltage known as electrical potential difference or electric tension (denoted ∆V and measured in volts, or joules per coulomb)which is the potential difference between two points — or the difference in electric potential energy per unit charge between two points. It is an important parameter of a source of energy which determines the amount of electric work to do.

Electric current - tidied up (directed) move of electric charges. Direct current or DC electricity is the continuous movement of electrons from an area of negative (−) charges to an area of positive (+) charges through a conducting material such as a metal wire. A DC circuit is necessary to allow the current or steam of electrons to flow. Such a circuit consists of a source of electrical energy (such as a battery) and a conducting wire running from the positive end of the source to the negative terminal. Alternating current (AC) electricity is the type of electricity commonly used in homes and businesses throughout the world. While direct current (DC) electricity flows in one direction through a wire, AC electricity alternates its direction in a back-and-forth motion. The direction alternates between 50 and 60 times per second, depending on the electrical system of the country.

Voltage is measured using voltmeters and electric current is measured using an ammeter

The accuracy of the conducted measurement depends on many factors which it is possible to divide in so-called mistakes and measuring uncertainties. We are dividing measuring errors into three groups: 1. approximation error, 2. mistake of the omission (systematic), 3. mistakes. Approximation errors result from simplifying conditions of measurement or from applying rough formulae. When approximation errors are bigger than measuring uncertainties, then one should enforce relevant amendments.

Mistakes of the omission (systematic) result from the inaccuracy of used devices, the false method of measurement or acting with difficulty of noticeable extrinsic factors. Badly made ruler, badly gauged measure they will cause, that the result will be systematically smaller or bigger than the actual value. Detecting the source of systematic errors is difficult and requires comparing used devices with the standard and the in-depth analysis of the method of measurement. At exercises performed in the student laboratory we usually assume that devices are free from systematic errors. Mistakes (gross errors) are coming into existence as a result of false reading out readings, of incorrect writing the result and the like mistakes are letting easily notice oneself and eliminate, since the received result differs from other results of measurements of the same size. In further analysis one should omit results burdened with the gross error.

The project is realized with the finance support of the European Commission within the "Longlife learning program". The presentation was made as a result of the Leonardo da Vinci project titled "Your future career prospects" carried out in "Zespół Szkół Zawodowych" no 3 in Katowice between 2011 and The publication reflects the standpoint of the authors only and neither the European Commission nor the National Agency bear responsibility for the essential contents included in the presentation and for the way of using the enclosed information.