Sphere P has twice the radius of sphere Q. P is initially at +400 V relative to infinity, and Q is at +100 V. The spheres are very far apart and are briefly connected with a thin conducting wire, then separated again. Which statement best describes their potentials after the wire is removed?
a) Both spheres come to a common potential of +300V, a value between their initial +100 V and +400 V, because the wire forces them to share the same potential.
b) Both spheres remain at +400V because the sphere that started at the higher potential dominates after contact.
c) Both spheres drop to +100V since charge flows until the lower-potential sphere is restored to its original value.
d) Both spheres settle at +250V, the simple average of their initial potentials, because potentials equalize by averaging.