Der Gerechte geht heim, doch sein Licht bleibt.


A machine is produced for the physic lessons in the HTL Mössingerstraße in Klagenfurt.   This machine measures approximately the speed of the light. This measurement is realized with the aim of the cheval mirror method from Foucault.

A laser beam is thrown through a half-mirror. A part of the laser is directly projected to the wall and the second part of the laser is thrown at the rotating hexagonal mirror. This deflected beam is diverted trough a mirror system and thrown back to the hexagonal mirror. Meanwhile this mirror has turned a little bit and that’s why the laser beam is reflected differently. As a result the second laser point occur a little displaced to the first one. Through the rotation speed of the mirror the distance travelled of the distracted laser beam and the distance between the two laser points at the wall the light speed is calculated.

With a wireless remote control the motor and the laser module can be switched ON or OFF. The desired rotation speed of the engine can also be adjusted by the remote control. This rotation speed is additionally displayed by a LC-Display on the control.

The real rotation speed of the engine which boosts the hexagonal mirror is controlled via a motor controller and displayed at a display which is integrated in the machine.

The program for the display, remote control and the motor controller are implanted in a microcontroller.

The used laser is green because this color is optimally identified by the eye.

Finally the light speed measurement is wired and installed in the physics room.

Light Speed Measurement