Question

The work function of a substance is 4.0 eV. The longest wavelength of light that can cause photo-emission from this substance is approximately (h = 6.63 × 10^-34 Js)[1eV = 1.6 × 10^-19 J]

Options

• 540 nm

• 400 nm

• 220 nm

• 310 nm

Answer 1

310 nm

Explanation:

`phi_0 = "hv"_0`

`lambda_0 = "hc"/phi_0`

`= (6.63 xx 10^-34 xx 3 xx 10^8)/(4 xx 1.6 xx 10^-19) = 3.10 xx 10^-7 = 310 xx 10^-9`