More digital confusion

Saturday 27 September 2014


As part of the long process of learning all the skills necessary to conduct an investigation in physics, my students have been doing a circus of mechanics experiments. The pair in the photo (Hamza and Maja) are using a Vernier motion sensor to measure the acceleration of a cart down a slope. The software plots a velocity time graph and the acceleration is found from the gradient. The problem was that the computer recorded movement that wasn't there. In fact the displacement time graph was fairly regular, as if something was moving backwards and forwards in front of the sensor. We tried changing the cables, sensor, computer then by chance realised that when the sensor pointed the other way it worked fine. In fact when it pointed away from Maja it worked fine. What is it about Maja that could cause this effect? Well Maja has cochlear implants maybe that's the reason. I have written to Vernier asking if this is possibly the cause, if not we will have to find out what else is in Maja's head.

NOS

This is quite a nice example of the nature of science.
  • An experiment was performed
  • the results were not as expected
  • variations of the experiment were carried out
  • a hypothesis was suggested
  • further experiment
  • theory researched
  • other scientists consulted

In an attempt to make a theory regarding the reason for this interference I researched how a cochlear implant works. A receiver picks up the sound and turns it into a digital signal that is sent to a coil. This coil is located next to a second coil that is under the skin, this coil is connected to electrodes implanted into the cochlea. The signal is transferred from the outer to inner coil by radio frequency electromagnetic signal and this is what could be interfering with the motion sensor. lets see what the experts say.


Update: I've not heard from Vernier yet but I have heard from Maja. Her implant is actually a bonebridge. This is similar in that there is transfer of data via coils between the inside and outside of the head but different in that instead of sending an electrical signal to the cochlea the bone of the skull is made to vibrate. Maybe this vibration is interfering with the signal? Pity the ear is no longer part of the syllabus.

Just got a reply from Vernier. Not a known problem but a source of ultrasound would interfere with the sensor.


Bambigeridoo
17 Oct 2014