A Level Physics Practice Exam

What is the condition for an electron to leave an atom?

1. It must be in the ground state

2. It must have enough excess energy

3. It must be in an excited state

4. It must be at a critical angle

The correct answer is: It must have enough excess energy

For an electron to leave an atom, it needs to overcome the attractive forces that bind it to the nucleus. This requires that the electron possesses a sufficient amount of energy, specifically more than the ionization energy of the atom. Ionization energy is the minimum energy needed to remove an electron from its ground state. When an electron has enough excess energy, it can overcome this binding energy and become free from the atom. This means that the condition for an electron to leave an atom hinges on whether it has acquired the necessary energy to break free from these attractive forces, which aligns perfectly with your choice. The other conditions mentioned do not inherently provide the necessary criteria for ionization; for example, whether the electron is in a ground state or excited state does not guarantee it has enough energy to escape. Additionally, the concept of a critical angle typically relates to phenomena like total internal reflection and does not apply to electron ejection in atoms.