In a straight conductor of uniform crosss section charge q is flowing for time t. Let s be the specific charge of an electron. the momentum of all the free electrons per unit length of the conductor . due to their drift velocity only is

Answer is q/ts

@raghavendra  I = nAeV_d  where n = no. of electrons per unit volume, A= area of cross section of the wire , e = charge of an electron , V_d = drift velocity

what we want is momentum per unit length of wire.(ie) mV_d , where m is the total mass of all electrons in the unit length of wire. here  I = (q/t) = nAeV_d . and m = n*(A*1)*(m_e). As n = no. of electrons per unit volume and A*1 is the volume of the unit length cross section and m_e is the mass of one electron.

Therefore mV_d  = (nAV_d)*m_e = (q*m_e)/(t*e)

As e/m_e = specific charge  = s,

mV_d  = q/(t*s)