19. A cylindrical copper rod has resistance R. It is reformed to twice its original length with change of volume. Its new resistance is:
a. R
b. 2R
d. R/2
c. 4R

The nuclear potential that binds protons and neutrons in the nucleus of an atom is often approximated by a square well. imagine a proton conned in an innite square well of length 105 nm, a typical nuclear diameter. calculate the wavelength and energy associated with the photon that is emitted when the proton undergoes a transition from the rst excited state (n 2) to the ground state (n 1). in what region of the electromagnetic spectrum does this wavelength belong?