# In image problems why negative charge is also earthed?

Suppose I have earthed conducting sphere of radius $$a$$ . And if we keep a change $$+Q$$ at a distance $$d$$ from the centre of the sphere then a charge of $$\frac {-Qa}{d}$$ will be induced $$\frac {a²}{d}$$ distance from the centre and $$\frac {Qa}{d}$$ charge at centre is grounded. But why not the $$\frac {-Qa}{d}$$ ? And similarly if I put $$+Q$$ and $$-Q$$ charge to the both sides of the sphere similar thing happens :- the positive charge at the centre is grounded? Why does that happen? I don't really understand. Please someone help as quick as possible.

• – Farcher Apr 26 at 6:46