Question

What should be the minimum work function of a metal so that visible light is able to cause emission?
(visible light$=$400-700 $nm$)

• A. 1.77 $eV$
• B. 1.87 $eV$
• C. 1.97 $eV$
• D. None of these

Answer 1

Answer: (A)

1.77 $eV$

We have

$E=\frac{hc}{\lambda }$

where, $E$, $h$, $c$ and $\lambda$ corresponds to the energy, Planck's constant, velocity of light and wavelength respectively.
Since we have to find the minimum work function, we will consider $\lambda =700nm$. (for highest wavelength, energy will be minimum )

$⟹E=\frac{\mathrm{6.6.25}\times {10}^{-34}\times 3\times {10}^8}{700\times {10}^{-9}}=2.84\times {10}^{-19}J=1.77eV$

So, the answer is option (A).