Consider a nonionized phosphorus donor atom in a si crystal.
(a) what is the "bohr radius" of the resulting "atom? "
(b) estimate how many si atoms are contained within a sphere of this "bohr radius"?
(c) estimate how high the concentration of impurities would have to be for the "bohr radii" to overlap, and what would you expect to happen in this case?

Why does the equilibrium position of the spring change when a mass is added to the spring? will the mass oscillate around the new equilibrium position of the spring or the previous position without a mass attached to the spring? if the equilibrium position of the spring changes by 20 cm (assuming no initial mass) when a mass is added to the spring with constant 4.9 kg/s^2, what is the mass of the object attached to the spring?