**Kirchhoff came up with two laws concerning conservation in electrical circuits.**

**First law**

It states that the sum of currents entering any point in a current is equal to the sum of the currents leaving that same point (conservation of charge). Electric charge is conserved in the circuits, all charge that arrive at a point must leave it.

In the figure,

Current going in = current going out

I_{1}= I_{2} + I_{3} + I_{4}

**Second Law**

It states that the sum of the e.m.f.s around any loop in a circuit is equal to sum of the p.d.s around the loop.

In the figure,

Energy givers = energy takers

ɛ = pd_{1} + pd_{2} + pd_{3} + pd_{4}

**Combinations of Resistors**

**Resistors in series**

If the three resistors R_{1}, R_{2} and R_{3} are connected in series. Then according to Kirchhoff’s first law; the p.d. V across the combination is equal to the sum od p.d.s across the two resistors:

V = V_{1} + V_{2 }+ V_{3}

Since V = IR,

So, IR = IR_{1 }+ IR_{2 }+ IR_{3}

Canceling common factors,

R = R_{1 }+ R_{2 }+ R_{3 }………..

**Resistors in parallel**

When three resisters of resistance R_{1}, R_{2} and R_{3} are connected in parallel. Using Kirchhoff’s law,

I = I_{1} + I_{2 }+ I_{3}

We know, I =

So, substituting the value of I and cancelling the common factor V we get,

1/R=1/R1+1/R2+1/R3 ………

**Ammeters have low resistance and are connected in series in a circuit.**

**Voltmeters have a high resistance and are connected in parallel in a circuit.**