# Determination of charge/mass value in E field.

1. Jun 17, 2006

### al_201314

I've been trying this out many times I just couldn't get the answer, I hope someone could help me out here.

A stream of nuclear particles are travelling horizontally at 3.9 X 10^6 ms^-1 are deflected as it passes through a vacuum between 2 parallel plates which are 5mm apart and 40mm in length. The P.D between the plates is 3000V and the angle of deflection is 4.3 degrees. Calculate q/m of a particle.

My working:

I first found out the field strength between the plates: dV/dr = 3000/0.005 = 600000 Vm^-1.

Then the time for which a particle is between the plates: 0.4/3.9 X10^6 = 1.0256 X 10^-7 s.

To find acceleration of a particle vertically downwards in terms of q/m would be => qE = ma, => a=qE/m = 600000q/m.

Horizontal velocity is after it leaves the E field would still be 3.9 X 10^6, while vertical velocity is vertical acceleration multiplied by the time, => (6.15 X 10^-3)(q/m) ms^-1.

I've found all I could, how can I solve for q/m? I tried using the equations for linear acceleration but they all consists of q/m on both sides which I cannot make the subject to determine the value.

Any help much appreciated.

alvin

2. Jun 17, 2006

### mukundpa

tan(4.3) = vy/vx