Elecrtric charges inmotion form electric current . Electric current is equal to the quantity of electric charges passing a given point in unit time . Conduction is the name given to a movement or flow of charges . The charges may be either positive or negative . In electrical circuits the flow of electric charges is considered to be a flow of electrons (negative charges) along a conductor or through a conducting medium . But charges may be ions when the conduction takes plane in gaseous or liquid conductors in which the ions are mobile .
To make electrons move though a metal conductor , there exists a driving force called electromotive force (e.m.f.) , which moves electric charges from one point in the circuit to another . When the e.m.f. is applied to the ends of the wire , the free electrons move in one direction . The greater the number of participating electrons , the greater is the flow of current .
As it is impossible to see electric current , its existence is provedby its effects . A current can heat a conductor , it can have a chemical action when passing through a solution , or it can produce a magmetic effect . The current can be measured by observing their heating , chemical or magmetic effects .
There exist several kinds of current : direct current , alternating current , pulsating current .
Direct current (d.c.) is an electric current that flows in one direction only and doesn't change its direction and magnitude at a constant resistance of a circuit .
The sources of direct current may be either galvanic elements , or thermoelements , or d.c. generators and accumulators . Besides , direct current may be obtained by converting alternating current into direct one with the help of rectifiers .
Almost all current calculations in d.c. circuits are based on Ohm's law . According to this law , any circuit section , connecting two points of this circuit not having electromotive force , contains current I = U/R , where U - voltage or potential difference between these two points , R - resistance of the circuit section connecting them . Ohm's law can be applied to the whole circuit in case there exists only one source of supply in it : I = E/R , where E - electromotive force of d.c. source of supply ; R - resistance of the entire circuit , including internal resistance of source of supply .
Alternating current (a.c.) is an electric current that changes both its direction and magnitude at fixed intervals of time . The strength of the current in alternating circuits , unlike that in direct ones , depends not only on resistance of the entire circuit and the voltage applied to it , but on the inductance and capacitance of the circuit sections as well .
Pulsating current is an electric current , alternative in its magnitude and stable , in its direction . It is produced when conversion of an alternating current into a direct current in current rectifiers , in anode circuits of electronic lamps etc. takes place .
To make electrons move though a metal conductor , there exists a driving force called electromotive force (e.m.f.) , which moves electric charges from one point in the circuit to another . When the e.m.f. is applied to the ends of the wire , the free electrons move in one direction . The greater the number of participating electrons , the greater is the flow of current .
As it is impossible to see electric current , its existence is provedby its effects . A current can heat a conductor , it can have a chemical action when passing through a solution , or it can produce a magmetic effect . The current can be measured by observing their heating , chemical or magmetic effects .
There exist several kinds of current : direct current , alternating current , pulsating current .
Direct current (d.c.) is an electric current that flows in one direction only and doesn't change its direction and magnitude at a constant resistance of a circuit .
The sources of direct current may be either galvanic elements , or thermoelements , or d.c. generators and accumulators . Besides , direct current may be obtained by converting alternating current into direct one with the help of rectifiers .
Almost all current calculations in d.c. circuits are based on Ohm's law . According to this law , any circuit section , connecting two points of this circuit not having electromotive force , contains current I = U/R , where U - voltage or potential difference between these two points , R - resistance of the circuit section connecting them . Ohm's law can be applied to the whole circuit in case there exists only one source of supply in it : I = E/R , where E - electromotive force of d.c. source of supply ; R - resistance of the entire circuit , including internal resistance of source of supply .
Alternating current (a.c.) is an electric current that changes both its direction and magnitude at fixed intervals of time . The strength of the current in alternating circuits , unlike that in direct ones , depends not only on resistance of the entire circuit and the voltage applied to it , but on the inductance and capacitance of the circuit sections as well .
Pulsating current is an electric current , alternative in its magnitude and stable , in its direction . It is produced when conversion of an alternating current into a direct current in current rectifiers , in anode circuits of electronic lamps etc. takes place .
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