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If φ is the work function of a photosensitive material in eV and light of wavelength of numerical value λ=(hc)/e metre is incident on it with energy above its threshold value at an instant, then the maximum kinetic energy of the photoelectron ejected by it at that instant is (in SI units): (Take h as Planck's constant and c as the velocity of light in free space)

Asked in NEET 2024 Re-exam · Work function and the photoelectric equation

• (1) e+2φ
• (2) 2e-φ
• (3) e-φ
• (4) e+φ

Step-by-step solution

Why the other options are wrong

• (1) comes from needs two slips at once, adding the work function instead of subtracting it and then counting it twice; no single error produces it
• (2) comes from doubling the photon energy. Substituting λ=hc/e into hc/λ gives e exactly once, with nothing left over to double
• (4) comes from the sign slip in Einstein's equation: the work function is the energy spent freeing the electron, so it is taken away from the photon energy, never added to it

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