The work function of a metal is 3 eV. The color of the visible light that is required to cause emission of photoelectrons is
- Red
- Green
- Blue
- Yellow
Answer
(3) Blue
Solution
Threshold wavelength 0 = hc 0 = 1240 eV nm3 eV 413 nm
Emission needs light of wavelength 0, i.e. light from the short-wavelength (violet–blue) end of the visible spectrum.
Red, yellow and green light have much longer wavelengths (lower photon energy) and cannot eject electrons.
Among the given colours, only blue lies at this high-energy end of the visible spectrum.
Answer: (3)