The bellows of an adjustable camera can be extended so that the largest film to lens distance is two times the focal length. If the focal length is 8 cm, the nearest object which can be sharply focused on the film must be what distance from the lens

Materials will have different energies associated with the electrons inside them. this is related to how strongly bound they are by their work function. if we sandwich a material with a very low energy between two materials with a high energy, we create a trap for an electron. if this trap is very narrow in one direction in comparison to the others, this is approximately a 1-dimensional box that confines the electron. what is the lowest energy of an electron in the box if the thinnest direction across the materials is 4.81 nm?