Q. The work functions of cesium (Cs) and lithium (Li) metals are 1.9 eV and 2.5 eV , respectively. If we incident a light of wavelength 550 nm on these two metal surfaces, then photo-electric effect is possible for the case of
A) Both Cs and Li
B) Neither Cs nor Li
C) Cs only
D) Li only
Explanation
[Solution by Dr. Abubacker] $E=\frac{1240}{550}\approx2.25$ eV. This exceeds the work function of Cs (1.9 eV) but not that of Li (2.5 eV). Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.