_____ uses light to allow current to flow.

• A. Electromagnetic Induction
• B. Capacitive Coupling
• C. Ohmic Conduction
• D. Photoelectric Effect

Answer: (D)

Light supplies the energy that frees electrons from a material in the photoelectric effect. When photons have enough energy (hf) to overcome the material’s work function, electrons are ejected from the surface. Those emitted electrons can then move as a current in a connected circuit. The stronger the light (more photons), the more electrons are emitted, up to limits, so the current increases with light intensity; if the light is below the threshold energy, no electrons are emitted and no current flows. This behavior is specific to light-induced emission, unlike electromagnetic induction (which relies on changing magnetic flux to make current), capacitive coupling (electric-field interaction without emission), or simple Ohmic conduction (current from a voltage across a conductor without light).