In the figure a particle of elementary charge e is initially
Solution
when particle is at z = 20 nm
suppose distance of dipole charge from origin is d.
PE of system = [k(q)(e) / (20-d)nm ] + [ k(-q)(e) / (20 + d)nm ]
= (9 x 10^9 x q x 1.6 x 10^-19) / (10^-9) [ 1/(20 -d) - 1/(20 + d) ]
= 1.44q [ 2d / (20^2 - d^2 ) ]
when charge e at z = 0
PE of system = [ k (q)(e) / sqrt(20^2 + d^2) ] + [ k (-q)(e) / sqrt(20^2 + d^2) ]
= [ k (q)(e) / sqrt(20^2 + d^2) ] - [ k (q)(e) / sqrt(20^2 + d^2) ]
= 0
initial PE = Wmax
Wmax = 2 vertical scale = 8 x 10^-30 ( i am liitlle confuse here whether it wil be 8 x 10^-30
or 2 x 10^-30 J)
1.44q [ 2d / (20^2 - d^2 ) ] = 8 x 10^-30
2.88qd = (20^2 - d^2) (8 x 10^-30 )
and d < < < 20
hence 20^2 - d^2 = 20^2
2.88qd = 400 x 8 x 10^-30
qd = 1.11 x 10^-27
(Or it will 0.278 x 10^-27 in other case when Wmax = 20 x 10^-30 J)
dipole moment = 2qd = 2.22 x 10^-27 Cm .........Ans
(or try 0.556 x 10^-27 C m )
