Phy question ...electricity A

a)(i) Charge density = (3.5 x 10^-15)/(4/3)pi.(2.31)^3 C/cm^3
Charge enclosed by sphere of radius 1.45 cm
= (3.5x10^-15) x (1.45/2.31)^3 C = 8.656 x 10^-16 C
Increase in potential at radius 1.45 cm
= (9x10^9).(8.656x10^-16)/0.0145 v = 5.373 x 10^-4 v
Hence potential = (5.373 x 10^-4 + 4x10^-4) v = 9.373 x 10^-4 v

(ii) Repeat the claculation using radius of 2.31 cm instead of 1.45 cm

(b)(i) Potential at A = (9x10^9).[-5/0.15 + 2/0.05]x10^-6 v = 60 000 v

(ii) Potential at B = (9x10^9).[-5/0.05 + 2/0.15] x 10^-6 v = -780 000 v

(iii) Work done = (3x10^-6).(60000 + 780000) J = 2.52 J

(iv) Increase

(v) Same work is done.