Which sensor type uses a wire coiled around a permanent magnet?

• A. Magnetic
• B. Hall-effect
• C. Optical
• D. Piezoelectric

Answer: (A)

Understanding how sensors translate physical changes into signals helps here: a wire wound around a permanent magnet uses electromagnetic induction. As the magnetic field from the magnet interacts with the coil, or as the magnet moves relative to the coil, a voltage is induced in the wire. This behavior is the hallmark of a magnetic sensor, which relies on a changing magnetic field and a conductor to generate a signal.

In contrast, Hall-effect sensors detect magnetic fields with a semiconductor element to produce a Hall voltage, optical sensors depend on light and detectors, and piezoelectric sensors generate charge from mechanical stress in a crystal. So the described coil-and-magnet setup fits the magnetic sensor category.