D.C. Circuits 49 Worked Example 2.8 Q For the network shown in Fig. 2.17 calculate the values of the marked currents. 40 A10 A80 A30 A25 AABCDI2I1I5I4I3FE Fig. 2.17 A Junction A: I 2 40 10 50 A Ans Junction C: so A IIII111280508030Ans Junction D: I 3 80 30 110 A Ans Junction E: so A IIII4344250258511Ans Junction F: so A IIIII54555308530308555Ans Note: The minus sign in the last answer tells us that the current I 5 is actually fl owing away from the junction rather than towards it as shown. 2.7 Kirchhoff ’ s Voltage Law This law also has already been used — in the explanation of p.d. and in the series and series/parallel circuits. This law states that in any closed network the algebraic sum of the emfs is equal to the algebraic sum of the p.d.s taken in order about the network. Once again, the law sounds very complicated, but it is really only common sense, and is simple to apply. So far, it has been applied only to very simple circuits, such as resistors connected in series across a source of emf. In this case we have said that the sum of the p.d.s is equal to the applied emf (e.g. V1 V2 E ). However, these simple circuits have had only one source