Practice portal › Dual Nature of Matter and Radiation › Einstein's Photoelectric Equation and Work Function
Asked in JEE Main 3rd April 1st Shift 2025 · Threshold frequency and wavelength
Given: φ=3 eV.
Threshold wavelength: λ₀=(1240 eV nm)/(3 eV)=413 nm.
Emission needs λ<413 nm, so the shortest wavelength on offer is the only candidate.
Of yellow, blue, green and red, blue is the shortest, so the printed key is blue.
Note: blue light runs from about 450 to 490 nm, which is 2.5 to 2.8 eV and still short of 3 eV. Strictly none of the four colours crosses the threshold, which sits in the violet.
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