Electrical Apprenticeship Exemption Practice Exam 2025 – Comprehensive Test Prep

Selenium exhibits unique semiconductor properties that are highly dependent on light exposure. In darkness, the conductivity of selenium decreases significantly due to the absence of photons that help excite electrons across the energy gap in the material.

In the presence of light, selenium's conductivity increases as electrons are promoted from the valence band to the conduction band, allowing for more free charge carriers and thus better conduction. However, when it is dark, this process is inhibited, causing the number of available charge carriers to drop and reducing its overall conductivity.

This phenomenon is particularly significant in applications such as photodetectors and solar cells, where selenium's light-response characteristics are exploited. Understanding this behavior is crucial for leveraging selenium effectively in various electronic applications, as its performance is greatly influenced by light conditions.