State Kirchhoff’s second law.
State the conservation law that gives rise to Kirchhoff’s second law
A circuit contains a cell of internal resistance 
and two resistors of resistances 
and 
as shown below.
The potential difference (p.d.) across the two resistors is 
. The current in the circuit is 
.
Use Kirchhoff’s laws to show that the total resistance 
of the external circuit is given by
The electromotive force (e.m.f.) of the cell in the figure above is 
. When the values of and are 
and 
respectively, the p.d. measured by the voltmeter is 
. Calculate the internal resistance of the cell.
A resistor of resistance 
is added in parallel to the circuit above.
State and explain the effect, if any, of this change on:
the current in the cell
the p.d. measured by the voltmeter.
.
