At threshold, photon energy = work function. E = hc/λ. So λ = hc/φ = 1240/4.2 = 295.2 nm ≈ 295 nm.
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JEE Main 2025 — Physics Modern Physics
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2025
Official previous-year question
Verified 30 May 2026.
Question
The work function of a metal is 4.2 eV. What is the threshold wavelength for photoelectric emission? (hc = 1240 eV·nm)
Options
- A
295 nm
- B
310 nm
- C
248 nm
- D
350 nm
Solution
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