In a series circuit can current ever be lost

In a series circuit what is the potential difference equal to

What do you have to take into account when determining the voltage of a cell

Apart from the potential difference, emf what also adds up to give the total in a series cicuit

In parallel what is the equation for current

Express 1/R=1/R1+1/R2 in another way
(this is only used in a parallel circuit)