Electricity

There are 2 NRICH Mathematical resources connected to Electricity
Hold still please
problem

Hold still please

Age
16 to 18
Challenge level
filled star empty star empty star
Can you arrange a set of charged particles so that none of them start to move when released from rest?
Placeholder: several colourful numbers
problem

Resistance

Age
16 to 18
Challenge level
filled star filled star filled star
Find the equation from which to calculate the resistance of an infinite network of resistances.