Conservation of charge and energy (c) recall Kirchhoff’s first law and appreciate the link to conservation of charge (d) recall Kirchhoff’s second law and appreciate the link to conservation of Energy

Kirchoff`s 1st law Sum of currents flowing into a point is equal to the sum of currents flowing out of that point

Conservation of charge Charge cannot be created or destroyed…. So current (charge per unit time) into a junction…. Must equal the charge per unit time flowing out.

Use it….. When analysing parrallel circuits

Kirchoff`s 2nd law Around any closed loop the sum of emfs is equal to the sum of p.d.s.

Emfs and p.d.s. What is the definition of emf? Or Energy tranferred (from other forms)/Charge passing round complete circuit. And p.d. Electrical potential energy tranferred (to other forms)/Charge passing between two points.

Conservation of energy Since the start point and end point are the same they must have the same energy. So the second law says “each coulomb of charge dissipates all the energy(p.d.s) that it gains (emfs) as it goes around a complete circuit.

Practise These can get quite tricky particularly when there is more than one emf in a parallel circuit. Problems are often combined with ideas of internal resistance and power.