Question

two electric charge of + 25 into 10 to the power minus 9 C minus 25 into 10 to the power minus 9 C are pleased 6 m apart. Find the field at electric field at point 4m on axial line from the center of the dipole.

Answer 1

Note that : Electric field due to dipole at axial Point from the center of dipole ,
E = 2kP / r ^3 -----( i )
Where ,
k = Coulomb's constant = 9 × 10^9
P = Dipole moment = q × 2a

Given : q = 25 × 10 ^-9 C
a = 6m

P = q × 2a = ( 25 × 10^-9 ) × 2 x 6 = 25 × 2 × 6 × 10^-9
= 50 x 6 × 10 ^-9
r = 4m

Putting values in ( i ) gives
E = 2kP / r ^3
= ( 2 × 9 × 10^9 × 50 x 6 x 10^-9 ) / ( 4 ) ^ 3
= { 2 x 50 × 6 ×9 × 10 ^ 9 + ( -9 ) } / 4 × 4 × 4
= 100 × 6 x 9 × 10 ^ 0 / 4 × 4 × 4
= ( 100 /4 ) × 6 × 9 × 1 × 1 / 16
= ( 25 × 6 × 9 ) / 16
= ( 25 × 3 x 9 ) / 8 ---- On dividing by 2
= 75 × 9 / 8
= 675 / 8
= 84.375 N/C ( approx..)