KIRCHHOFF'S LAWS

In solving problems and analysing circuits we need to consider two very important conservation laws. Any conservation law in physics makes it easy for physicists to predict what will happen sometime later as some quantity won’t change. ==Kirchhoff’s First Law== Charge conservation: The total charge entering a junction is equal to the total charge leaving the junction. [image:http://i.imgur.com/2Mb7a7H.png] Put simply: $$Q= Q_1+ Q_2$$ and therefore since $$I = \frac{Q}{t}$$ we have $$I= I_1+ I_2$$ ==Kirchhoff’s Second Law== '''Energy Conservation''': Around a closed circuit loop, the total '''EMF''' is equal to the total '''PD'''. Another way to look at this is that all of the electrical potential energy gained by the charge in a DC circuit is lost to other forms around a complete circuit loop. $$\sum E = \sum V$$ We examine this in a simple way following from our definitions of EMF and PD and looking at an example circuit below. [image:http://i.imgur.com/JqrpCKE.png] Indeed if we add up the energies per unit charge where energy is being converted from electrical potential to other forms that 9V EMF = 9V PD. No matter how many things we add in series, this rule has to be true. [image:http://i.imgur.com/gXeJcS9.gif]