physics
posted by chandankumar .
if electron are caused to fall through a potential difference of 100000 voltage , determine their final speed if they were initially at rest.

e*100,000 is the kinetic energy.
e is the electron charge,1.6*10^19 C
Set 100,000*e equal to (1/2)mV^2 and solve for V
m is the electron mass. 
6646

p.d.=100000V
therefore, workdone , W=q×p.d.
W=1.6×10^19 × 100000
=1.6×10^14 Joules
since work done = force × displacement
F×s=1.6×10^14
m×a×s=1.6×10^14
9.1×10^31×a×s=1.6×10^14
a×s=(1.6×10^14)÷(9.1×10^31)
a×s=1.75×10^17
v^2/2=1.75×10^17
v=5.09×10^8m/s 
Recall that one electronvolt is the energy gained by an electron in moving through a potential difference of 1 V, so
1 eV = 1.6 * 10^19 Joules
1,000,000 V = 1.6 ^ 10^19 * 10^6 Joules = 1.6 * 10^13 J
So this must be the kinetic energy gained be the electron.
KE = (1/2) m v^2
From reference tables
mass of electron = 9.11 * 10^31 kg
So
1.6 * 10^13 = (1/2) * 9.11 * 10^31 * v^2
v^2 = 2 * 1.6 * 10^13 / 9.11 * 10^31 = 0.35 * 10^18
v = 0.59 * 10^9 m/s