Which quantity does a Hall effect sensor sense?

• A. Light
• B. Magnetic field
• C. Sound
• D. Temperature

Answer: (B)

A Hall effect sensor measures magnetic fields. When a current flows through a thin conductor and a magnetic field is perpendicular to that current, charge carriers experience a sideways force that creates a small voltage across the material—the Hall voltage. This Hall voltage is proportional to the magnetic field’s strength, so the sensor output reflects the magnetic field present. That makes Hall sensors ideal for detecting proximity to magnets, measuring position or speed, and even sensing current by monitoring the magnetic field around a conductor.

Light, sound, and temperature are detected by entirely different phenomena and sensors (photodetectors for light, microphones for sound, thermistors/RTDs for temperature), which is why those options don’t fit.