Which idea did Ptolemy's model use to explain why the planets appeared to move backward as they moved in their orbits? The planets spun in epicycles. The planets rotated on their axes. The planets revolved around the Sun. The planets were made of different materials.

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?