Umthetho wokuqala kaKirchhoff obizwa nangokuthi umthetho wendawo yokuhlangana uthi ugesi ongena endaweni yokuhlangana ufana nogesi ophuma kuleyo ndawo yokuhlangana. Indawo yokuhlangana esisekweni sikagesi yindawo lapho kuhlangana khona ababili noma ngaphezulu kwabaqondisi ababili, njengephuzu u-a esithombeni ohlangothini.
I ingugesi ongena endaweni yokuhlangana, kuyilapho u-I 1 no-I 2 kuyimisinga kagesi ephuma endaweni yokuhlangana, I = I 1 + I 2. Esinye isibonelo, bheka isithombe esingezansi.
Ngingu-ozayo okwamanje kagesi, ngenkathi mina1, Mina2, nami3 yiziphethu zikagesi eziphumayo, I = I1 + Mina2 + Mina3.
Umthetho wokuqala kaKirchhoff usekelwe emthethweni wokulondolozwa kweshaja kagesi othi ishaja ingunaphakade, ishaja kagesi engenayo kumele ilingane neshaja kagesi ephumayo, akukho shaja kagesi elahlekayo. Ugesi kagesi uyishaja kagesi egeleza phakathi nesikhathi esithile. Ugesi ongena endaweni yokuhlangana ufana nogesi ophuma kuleyo ndawo yokuhlangana.
Umthetho wokuqala kaKirchhoff owashiwo nguGustav Kirchhoff (1824-1887), isazi sefiziksi saseJalimane.
Inkinga yesampula 1:
I 1 = 2 A, I 2 = 3 A, I 3 = 5 A, I 4 = 3 A. Thola I 5!
Isixazululo:
Ngiyangena = ngiyaphuma
Mina 1 + Mina 3 = Mina 2 + Mina 4 + Mina 5
2 A + 5 A = 3 A + 3 A + I 5
7 A = 6 A + I 5
I 5 = 7 A – 6 A
I 5 = 1 A
Inkinga yesampula 2:
I = 10 A, I 1 = 2 A, I 2 = 4 A. Thola I 3!
Isixazululo:
Ngiyangena = ngiyaphuma
Mina = Mina 1 + Mina 2 + Mina 3
10 A = 2 A + 4 A + I 3
10 A = 6 A + I 3
I 3 = 10 A – 6 A
I 3 = 4 A
