A photodetector converts energy from which form to electrical energy?

• A. Light to electrical
• B. Electrical to light
• C. Light to heat
• D. Electrical to magnetic

Answer: (A)

Photodetectors are devices that respond to light by producing an electrical signal. When photons enter the semiconductor, their energy is absorbed and can promote electrons from the valence band to the conduction band, creating electron–hole pairs. An internal electric field or an applied bias then separates these charge carriers, generating a current or voltage that can be measured. This is a direct conversion of light energy into electrical energy, which is why light to electrical is the right description. The other possibilities describe different energy conversions—electrical to light (as in LEDs), light to heat (photothermal effects), or electrical to magnetic (changing magnetic fields)—which aren’t what a photodetector does.