photogate

A photogate is an electronic device used to measure the time an object takes to pass through a specific point. It consists of a light source and a light detector positioned opposite each other. When an object interrupts the beam of light between the source and the detector, the photogate registers the interruption. This interruption signals the start or end of a timed interval.

Photogates are commonly used in physics experiments to measure velocity and acceleration. By placing two photogates a known distance apart, the time it takes for an object to travel between them can be measured. Knowing the distance and time, the average velocity can be calculated. If the object is accelerating, the velocity measured over shorter intervals can reveal the rate of acceleration.

The mechanism involves an infrared or visible light beam. The detector is typically a phototransistor or photodiode that changes its electrical output when the light beam is broken. This change in output is then processed by a timer, which can be a dedicated timer unit or integrated into a data acquisition system. When the light beam is re-established, the timer stops. The precision of a photogate depends on the speed of its response time and the accuracy of the associated timer. They are essential tools for hands-on learning in mechanics and kinematics, providing accurate and repeatable measurements.