This diagram shows two parallel metal plates which have beenplaced 8cm apart and
ID: 1675728 • Letter: T
Question
This diagram shows two parallel metal plates which have beenplaced 8cm apart and charged so there is an electrical potential of200V between them. a) What would be the magnitude and direction of the electricalforce on an electron placed at point B? How would the force change at point C? b) What would be a reasonable estimate of the electricalpotential at point A? c) Would an electron gain or lose electrical potential as itmoves from points B to C? d) What would be the speed of a protonwhen it strikes the negativeplate if it started from the positive plate?
Explanation / Answer
a) Electrical field between the plates, E = Potential difference /distance between plates = V/d = 200/0.08 = 2500 V/m Force on electron = qE = e x 2500 = 1.602 x10-19 x 2500 = 4005 x 10-19 N Since the electric field is uniform between theplates, the force is same whether it is placed at A, B, or C b) Assuming potential of -ve plate to be zero, Since, electric field is uniform, potential willuniform increase from -ve to +ve plate. Potential at mid-point will be 100 V c) electron will move from higher potential (point B) regionto lower potential region (point C). But its potential energy will increasesince it is negative charge. d) work done by electric field = F x d = 4005 x10-19 x 0.08 = 320.4 x 10-19 J work done = change in K.E. 0.5mv2 = 320.4 x10-19 v =195732 m/s