A Level Physics Practice Exam

What is the primary reason emitted electrons' kinetic energies vary?

1. The constant frequency of the incident light

2. Differences in energy required to release different electrons

3. The mass of the emitted electrons

4. The intensity of the emitted light

The correct answer is: Differences in energy required to release different electrons

The variation in the kinetic energies of emitted electrons is primarily attributed to the differences in the energy required to release different electrons from within the material. When light of a certain frequency strikes a material, it can provide enough energy to eject electrons. However, not all electrons are bound to their atomic nuclei with the same energy; some are more tightly bound (require more energy to be released), while others are less tightly bound (require less energy). This means that when photons collide with these electrons, the excess energy after overcoming the binding energy results in varying kinetic energies of the emitted electrons. If the energy from the incident photons is greater than the binding energy of the electrons, the difference contributes to the electrons' kinetic energy once they are emitted. Therefore, the specific binding energy associated with different electron configurations and levels in the material directly impacts the kinetic energy of the emitted electrons.