# Need help with this question (1 Viewer)

#### Danneo

##### Member
Its from a past paper, forgot which year

'Two parralel plates are 2mm apart and have a potential difference of 100V between them. An electron is placed halfway between the plates

What is the magnitude of the force on the electron'

Any help great appreciated, thx

#### jazz519

##### Well-Known Member
Hi, so we need to know the equations that describe what occurs when there are parallel plates. The electric field strength at all points inside the parallel plates is equal and therefore the statement about being halfway between the plates is irrelevant. The field strength is given by the expression E = V/d, and the force on a particle due to an electric field in general we know is F = qE

So using equation 1, E = 100/(2x10^-3) = 50000 V/m (*note that the distance value should be in S.I. units i.e. which is metres so convert 2mm = 2x10^-3 m)

Now F = qE = (1.602*10^-19)(50000) = 8.01 * 10^-15 Newtons

(q is charge of electron you can find that on your data sheet)