A photocell calculator

You will write three small functions for a photocell. Use $hc = 1240$ eV nm.

The idea. A photon of wavelength $\lambda$ in nm has the energy $1240/\lambda$ in eV. The largest kinetic energy is the photon energy minus the work function, and it cannot be below zero: when the photon has too little energy, no electron leaves. A beam of power $P$ sends $P/E$ photons each second.

Your tasks.

1. In photon_energy, return the energy in eV of a photon of wavelength wavelength in nm.
2. In max_kinetic_energy, return $K_{\max}$ in eV for a metal with work function phi in eV. If no electron can leave, return 0.
3. In photocurrent, return the current in A for a beam of power power in W, when a fraction efficiency of the photons each free one electron.