Question

A $15.0eV$ photon collides with and ionizes a hydrogen atom. If the atom was originally in the ground state (ionization potential $=13.6eV$), what is the kinetic energy of the ejected electron?

• A. $1.4eV$
• B. $13.6eV$
• C. $15.0eV$
• D. $28.6eV$

Answer 1

Answer: (A)

$1.4eV$

Conservation of energy requires that the $15.0eV$ photon energy first provides the ionization energy to unbind the electron, and then allows any excess energy to become the electron's kinetic energy.

The kinetic energy in this case is $15.0eV-13.6eV=1.4eV$