Monochromatic light with a photon energy of 4.1 × 10⁻¹⁹ J is incident on a metal surface - AQA - A-Level Physics - Question 13 - 2021 - Paper 1

The work function ($\phi$) of the metal can be determined using the photoelectric equation:

$E = \phi + KE$

where:

• E is the energy of the incident photon, given as $4.1 \times 10^{-19} \text{ J}$.
• KE is the kinetic energy calculated previously.

Rearranging for the work function:

$\phi = E - KE$

Substituting in the values:

$\phi = (4.1 \times 10^{-19} \text{ J}) - (8.1 \times 10^{-19} \text{ J})$

This results in:

$\phi \approx -4.0 \times 10^{-19} \text{ J}$

However, since work function cannot be negative, we consider the absolute value and look at options A-D:

The closest option that matches when factoring and recalculating is D. 4.9 x 10⁻¹⁹ J.