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Kirchhoff Rules, , (a)Kirchhoffs First Rule - Junction Rule:, , At any junction, the sum of the currents entering the junction is equal to the, sum of currents leaving the junction. 1 =0 ., , \e, , ly sb, 1 th+=1, +1,, I, +12 — Is +1,-I5=0, Y1=0, , i; ly, , Kirchhoff’s junction rule is in accordance with law of conservation of charge., , (b)Kirchhoffs Second Rule -Loop Rule, The algebraic sum of changes in potential around any closed loop is, zero. >, AV = 0, , |, , , , , , ' If Path from —ve to +ve terminal, AV= + & :, For Loop ABCDA | If Path from +ve to -ve terminal AV= - &, = | For resistor :, £, —IR; — £2 — IR,=0 ' If path is in same direction of current AV=- IR, ‘ If path is in opposite direction of current AV= -+HIR |, , Kirchhoffs Loop rule is in accordance with Law of conservation of energy.
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Wheatstone Bridge, , , , For a balanced Wheatstone’s bridge , the resistors are such that the current, through th galvanometer I, = 0., , Apply Kirchhoff's junction rule to junctions B, , I, =I, -------------(1), Apply Kirchhoff's junction rule to junctions D, I, 2h (2), , Apply Kirchhoff's loop rule to closed loop ABDA, = I,Ry+ I, R,=0, , Apply Kirchhoff’s loop rule to closed loop CBDC, , 14R4 — I, Ry=0, I; Rg= 1,Ry --------------(4), eq), Ra _ Re, eq (4) I,R3 [,Rq, Ba, Ra, Rg Ry, Bs Be, , Ry Rg
