If we stretch the wire to double its length what will be effect on drift velocity?

I will answer the question considering the following 2 cases :-

1. The length of the weir is doubles but the cross sectional are of the wire is not changes ( 2 wires of same crooks sectional area and made up of the same material are connected end to end and the same potential difference is applied) - In this case the resistance of the wire increases 2 times. Since drift velocity of electrons is inversely proportional to the resistance of the wire, it becomes one half.

I = N×E×A×V

I=current

N= no. Density of electrons

A= area of cross section of the wire

V= drift velocity.

I is inversely proportional to R and thus V is also inversely proportional to R.

2. The length of the wire is doubled and thus cross section of the wire gets halved - In this case the resistance of the wire increases by 4 times and thus drift velocity becomes one fourth.