A4. A photon with an energy of 13.6 eV knocks an electron out of a hydroge atom. The kinctic energy of the ejected electron is cqual to __ eV. 1. 13.6 2. 3.4 3. 10.2 4. 0

The correct answer is 4. 0 eV.<br /><br />When a photon with an energy of 13.6 eV knocks an electron out of a hydrogen atom, the process is known as the photoelectric effect. In this case, the photon's energy is used to overcome the binding energy of the electron in the hydrogen atom, which is also 13.6 eV. As a result, the kinetic energy of the ejected electron is zero eV because all the photon's energy is used to ionize the hydrogen atom, leaving no energy left for the electron's kinetic energy.