A mettalic sphere of radius a carries a charge Q. It is brought in contact with an uncharged sphere of radius b . what will be the charge on the first sphere.

My work
I eliminated 2 options by substitution and realised that it won't be their average as they don't have same charge capacities

3 answers

they will have equal charge densities when touched, so current wont flow.

Charge densitya=q1/4PIa^2
charge densityb=q2/4PIb^2

remember q1+q2=Q You are looking for q1.

set them equal, and you get
q1/a^2=q2/b^2

q1=(a/b)^2 (Q-q1) let a/b=k
q1=kQ-kq1

q1=kQ/(1+k)

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