When a certain material is illuminated with visible light, electrons jump from lower to higher energy states in atoms of the material. When illuminated by ultraviolet light, atoms are ionized as some of them eject electrons. Why do the two kinds of illumination produce such different results?
UV light has more energy than visible light; therefore, the UV light has the potential to move the electrons far enough so that the electrons are in an ionized state.
The difference in the results obtained when a certain material is illuminated with visible light versus ultraviolet light can be understood by examining the energy levels of the atoms in the material.
In an atom, electrons occupy specific energy levels or "shells" around the nucleus. These energy levels are quantized, meaning that electrons can only occupy certain specific energy states. When an atom is illuminated with visible light, which has lower energy than ultraviolet light, the electrons in the atom can absorb enough energy from the light to jump to higher energy levels within the atom. This process is known as excitation. The electron absorbs the energy from the visible light and moves from a lower energy level to a higher one.
On the other hand, when atoms are illuminated with ultraviolet light, which has higher energy than visible light, the atoms may absorb enough energy for electrons to be completely removed from the atom. This process is known as ionization. The high-energy ultraviolet light can provide enough energy to the atoms to overcome the attractive force between the electron and the nucleus, causing the electron to be ejected from the atom, resulting in ionization. The electrons that are ejected from the atom are known as photoelectrons.
So, the different results observed when a certain material is illuminated with visible light versus ultraviolet light can be attributed to the difference in energy levels of the atoms and the ability of the light to either excite the electrons to higher energy states or ionize the atoms by ejecting electrons completely. Visible light is typically not energetic enough to cause ionization, while ultraviolet light has sufficient energy to overcome the forces binding the electron and nucleus, leading to ionization.