A Level Physics Practice Exam

What happens to the charge of a positive plate when electrons are ejected due to ultraviolet light?

1. The charge becomes neutral

2. The charge increases

3. The charge decreases

4. The charge remains the same

The correct answer is: The charge increases

When ultraviolet light is shone onto a positive plate, it provides energy to the electrons within the material. This energy can be sufficient to overcome the binding forces holding the electrons to the atoms in the plate, allowing them to be ejected. As electrons carry a negative charge, the removal of these negatively charged particles results in a net increase in positive charge on the plate. This can be understood through the concept of charge conservation. Before the ejection, the plate has a certain positive charge, and ejecting negative charges (electrons) means that there are fewer negative charges to balance out the positive ones. Therefore, the overall effect is that the positive charge of the plate increases as a result of losing negatively charged electrons due to the illumination from ultraviolet light.