Question

An α particle is accelerated through potential difference of 2000 V.... Calculate K.E

Answer 1

When a particle of charge (Q) and mass (M) is accelerated through a potential difference(V), work (W) is done by  the electric filed which changes kinetic energy(KE).
Work done by the field = change in kinetic energy
Work done by the field = final kinetic energy - initial kinetic energy
If particle starts from rest then initial kinetic energy is zero.
Then, Work done by the field = final kinetic energy 
Work  s done by  the electric filed = charge X potential difference.

W = QV = KE

Charge of α particle Q = 2× $1.6\times10 ^{-19}$ C


    KE = W = 2× $1.6\times10 ^{-19}$×2000= 6.4 x 10^-16 J