JEE MainPhysicsDual Nature of Matter
A metal surface is illuminated separately by two different monochromatic light sources. It is observed that a 10 W blue light source of wavelength 450 nm causes photoelectric emission, but a 100 W yellow light source of wavelength 580 nm does not cause any emission. If _ th is the threshold wavelength for the metal, which of the following conditions must be true?
Options
- A_ th > 580 nm
- B450 nm _ th < 580 nm
- C_ th < 450 nm
- D_ th = 515 nm
Correct answer
B. 450 nm _ th < 580 nm
Step-by-step solution
For photoelectric emission to occur, the incident wavelength must be less than or equal to the threshold wavelength _ th . Since the 10 W blue light ( = 450 nm ) causes emission, its wavelength must be less than or equal to the threshold wavelength: 450 nm _ th Since the 100 W yellow light ( = 580 nm ) does not cause emission despite its higher power (power only affects the number of photons, not their individual energies), its wavelength must be strictly greater than the threshold wavelength: 580 nm > _ th Combini