What is the electric field strength between the disks?
A proton is shot from the negative disk toward the positive disk. What launch speed must the proton have to just barely reach the positive disk?
3 Answers

The electric field between the plates is
E = σ/εo… where σ = area charge distribution
= 10X10^9/(π*(0.010m)^2) = 3.183×10^5C/m^2
and εo = 8.854×10^12C^2/Nm^2
So E = 3.183×10^5C/m^2/8.854×10^12C^2/Nm^2 = 3.60×10^6N/C
Using conservation of energy we solve the second part
(K + U) b = (K + U)t…Here Ut – Ub = q*(Vt – Vb)…and Vt – Vb = E*d = 3.60×10^6V/m*1.0×10^3m = 3595V
Since Kt = 0 we have Kb = q*E*d = 1.60×10^19C*3595 = 5.75×10^16J
So 1/2*m*v^2 = 5.75×10^16J
Therefore v = sqrt(2*5.75×10^16J/m) = sqrt(2*5.75×10^16J/1.67×10^27kg) = 8.30×10^5m/s

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