Question

The photogates in the experiment are used to determine the speed of the gliders passing through. The photogates measure the time it takes for the photogate beam to go from being unblocked to blocked to unblocked again. You tell the photogate how long your glider is, and the speed is then calculated.

Given the description of what the photogates do, how will you determine the velocity of the glider?

Answer 1

Consider an arrangement as shown below.

A Photodetector is a device that allows electricity to pass through it, if a particular of light falls on it. Consider it as a switch, but instead of manually turning it on and off, it will automatically turn on and off depending on whether light falls on it. The arrangement can be programmed, so that current passes through it if the light stops falling on the detector.

Once the block is in between the laser and the detector, light stops to fall on the detector, and a voltage change occurs. The voltage comes back to its initial value once the block completely passes through and the laser light falls on the detector again.

Using a programming software, the time taken for the signal to come back to its initial state can be measured.

This is the time taken by the block to fall a distance equal to its own length.

Using speed = distance/time, the velocity of the glider can be calculated.