Two metallic spheres of radii 1 cm and 3 cm are given. . .

Question : Two metallic spheres of radii 1 cm and 3 cm are given charges of -1×10^-2 C and 5×10^-2 C, respectively. If these are connected by a conducting wire, the final charge on the bigger sphere is [AIPMT 2012]

(A) 2×10^-2 C

(B) 3×10^-2 C

(C) 4×10^-2 C

(D) 1×10^-2 C

Doubt by Nevaeh

Solution : 

Q₁+Q₂=Q

Q₁=-1×10^-2 C

Q₂=5×10^-2 C

So

Q=4×10^-2 C

Final Charge 

Q₁'=?

Q₂'=?

But As per the law of conservation 

Q₁'+Q₂'=Q

Q₁'+Q₂'=4×10^-2 C

V₁=V₂

kQ₁'/R₁=kQ₂'/R₂

Q₁'/1=Q₂'/3

Q₁'/Q₂'=1/3

Now Charge on bigger sphere

Q₂'=[3/4]×4×10^-2 C

Q₂'=3×10^-2 C

Hence, (B) 3×10^-2 C, would be the correct option.