Which type of sensor uses light to track position?

• A. Mechanical
• B. Digital
• C. Photo-electric or optical
• D. Magnetic

Answer: (C)

The key idea is sensing position by using light. Photo-electric or optical sensors emit a beam of light (usually infrared) and detect changes in that light to determine where something is or how far it has moved. Because they rely on light, they can measure position without any physical contact, which gives high resolution and reduces wear. In robotics, this shows up as optical encoders that read rotation with a slotted wheel or photoelectric units that detect the presence or absence of a target. This is different from mechanical sensors that need contact, magnetic sensors that rely on magnetic fields, or generic digital sensors that aren’t inherently about light-based position tracking. So the type that uses light to track position is the photo-electric or optical sensor.