Q87 / 90 · JEE Main 2024 (30 Jan Shift 1) · Physics

The work function of a substance is $3.0 eV$ . The longest wavelength of light that can cause the emission of photoelectrons from this substance is approximately:

Solution

For longest wavelength, the emitted electron will have nearly zero kinetic energy.

Therefore,

$λ = \frac{h c}{W_{e}}$

$\Rightarrow λ = \frac{1240 nm - eV}{3 eV}$

$\Rightarrow λ = 413.33 nm$

$\Rightarrow λ_{\max} \approx 414 nm$

Hence, the correct answer is option: 'B'.