Question
Thu June 23, 2011

# The distance between the plates of condenser is 2 cm.Starting from rest an electron taken 1.5*10^-8 seconds to reach from negative to positive plates.What is the potential difference between the 2 plates?

Fri June 24, 2011
Let the potential difference between plates is V.

Then, electric field, E= V/0.02 volt/m

Force on the electron, F = q E

The acceleration, a = F / me = q E / me = q V / (0.02 x me)

Now using the second equation of motion

s = u t  + (1/2 ) a t2

0.02 = 0 + (1/2 ) q V t/ (0.02 x me)

0.02 = q V t2/ (2 x 0.02 x me)

V = 0.02 x 2 x 0.02 x me / q t2

V = 8 x 10-4 x 9.1 x 10-31 / 1.6 x 10-19 x 1.5 x 1.5 x 10-16

V = 8  x 9.1 / 1.6 x 1.5 x 1.5

V= 20.22 volts

the speed of the electron = 0.02 / 1.5 x 10-8 = (4/3) x 106 m/s

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