A negative charge -Q is placed inside the cavity of a hollow metal solid. The outside of the solid is grounded by connecting a conducting wire between it and the earth. Is any excess charge induced on the inner surface of the metal? Is there any excess charge on the outside surface of the metal? Why or why not? Would someone outside the solid measure an electric field due to the charge -Q? Is it reasonable to say that the grounded conductor has shielded the region outside the conductor from the effects of the charge -Q? In principle, could the same thing be done for gravity? Why or why not?

the electric field inside the conductor is zero because the charge in the cavity is negative charge. if the inner surface of the conductor must have the opposite charge of the cavity, then zero electric field inside the conductor is there. Thus, it has an excess of electrons

the surface of the sphere is connected to the ground because the earth is a good conductor so the excess electrons on the surface of the sphere will flow to the ground. Thus, there is no excess charge on the outside surface of the metal. That is shown in the diagram.

the excess electrons on the surface are removed by the ground and the net charge on the sphere will be zero thus, no electric field is applied outside the sphere. Thus, outside the solid measure there is no electric field due to the charge.

the electron's mass is very small and the gravity depends on the mass of the elements thus it will be difficult for gravitational force to act as a ground or shield. Thus, the same thing cannot be done for gravity