A Level Physics Practice Exam

In the context of the work function, what does Ek represent?

1. The total binding energy of the outer electrons

2. The maximum kinetic energy of an electron after leaving an atom

3. The energy difference between the ground state and the ionized state

4. The kinetic energy an electron gains after being accelerated

The correct answer is: The maximum kinetic energy of an electron after leaving an atom

In the context of the work function, \(E_k\) represents the maximum kinetic energy of an electron after leaving an atom. This concept is rooted in the photoelectric effect, where electrons are emitted from a material after absorbing energy, typically from photons. When electromagnetic radiation strikes a material, electrons can absorb energy from the photons. The work function is the minimum energy required to overcome the attractive forces that bind an electron to its atom. If the energy of the incoming photon exceeds this work function, the excess energy will be converted into kinetic energy of the emitted electron. Thus, the kinetic energy \(E_k\) can be expressed by the equation: \[ E_k = E_{photon} - \phi \] where \(E_{photon}\) is the energy of the incident photon and \(\phi\) (the work function) is the energy required to liberate the electron. Therefore, \(E_k\) is indeed the maximum kinetic energy of the ejected electron after it has overcome the binding energy and escaped the atom. This understanding is central to explaining phenomena such as the photoelectric effect, where the observation of emitted electrons upon light exposure directly relates to their kinetic energy, dictated by this relationship.