Question

The work function of a photosensitive material is
4.0 eV. The longest wavelength of light that can
cause photon emission from the substance is
(approximately)
[NEET - 2019 (Odisha)]
(1) 310 nm
(2) 3100 nm
(3) 966 nm
(4) 31 nm

Answer 1

answer : option (1) 310 nm

work function of a photosensitive material is 4 eV.

we know, 1eV = 1.6 × 10^-19 J

so, work function = 4 × 1.6 × 10^-19 J

let's find threshold wavelength,

work function, Φ = hc/λ

⇒4 × 1.6 × 10^-19 J = 6.625 × 10^-34 × 3 × 10^8/λ

⇒λ = (6.625 × 3 × 10^-26)/(6.4 × 10^-19)

⇒ λ = 3.1 × 10^-7 m = 310 nm

for emission of photons from metal surface, wavelength must be less than or equal to threshold wavelength.

hence, maximum wavelength = threshold wavelength = 310 nm

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Answer 2

$\huge\star\mathfrak\blue{{Answer:-}}$

$\huge\bold\purple{option (1) 310 nm}$