1. When light of wavelength 1 is incident on a certain photoelectric cathode, no electrons are emitted...

Question:

1. When light of wavelength λ1 is incident on a certain photoelectric cathode, no electrons are emitted no matter how intense the incident light is. Yet when light of wavelength λ2 < λ1 is incident, electrons are emitted even when the incident light has low intensity. Explain.

2. The distance between Li+ and Cl- ions in a LiCl crystal is 0.257 nm. Find the energy of electrons that have a wavelength equal to this spacing.