Which sensor outputs a voltage when a magnetic field is present?

• A. Hall effect sensor
• B. Magnetic reed switch
• C. Photoelectric sensor
• D. Capacitive sensor

Answer: (A)

The fundamental idea here is that a Hall effect sensor directly converts a magnetic field into an electrical signal. When a magnetic field passes perpendicular to the current in a conducting element, charge carriers are deflected and produce a voltage across the sensor—the Hall voltage. This output is proportional to the magnetic field strength, so the sensor provides an electrical voltage that indicates the presence (and even the magnitude) of the magnetic field. Some Hall sensors give a continuous analog voltage, while others include an internal threshold to produce a digital signal when the field crosses a set level.

In contrast, a magnetic reed switch is a mechanical switch that closes a circuit in the presence of a magnetic field but does not generate a voltage on its own. A photoelectric sensor uses light to detect objects, not magnetism, and a capacitive sensor detects changes in capacitance due to nearby materials, also unrelated to magnetic fields.