JEE Main levelNumerical answerDifficulty 2 of 3as022
The work function of a metal is 2.3eV. Find the threshold wavelength in nm, to the nearest integer. Use h=6.626×10−34Js, c=3.0×108ms−1, 1eV=1.6×10−19J.
Numerical answer type, answer in nm, tolerance 1.
Answer: 540 nm
W = 2.3 x 1.6e-19 = 3.680e-19 J. The threshold wavelength is where hc/λ = W, so λ0 = hc/W = 1.9878e-25/3.680e-19 = 5.402e-07 m = 540.2 nm, i.e. 540 nm.