News

Magnetic Field of a Current Loop

The web form to collect the data (as part of an online script).

I just had a look at the data of our latest experiment assignment for our students. Just like in our previous collective measurement of pendulum frequencies, the students were supposed to submit their results through an online form, so we can combine all the data to test a model that will be discussed in an upcoming lecture. This time, they should measure the magnetic field generated by a current loop.

Since we could not expect that every student has got an adjustable current available, we instructed them to simply use an AA battery (non rechargeable, non Lithium, etc. for safety reasons) and connect it to any cable (like the USB cable in the picture above). After finding the location of the magnetometer in their phones, they simply should create a loop with the magnetometer in its center and measure the change in the magnetic field perpendicular to this loop. Repeat five times with varying radius and submit the results:

Since we do not know the actual current used in this experiment (at 1.5V this still depends on the cable and the battery’s internal resistance), we told them to include one measurement at a radius of 5cm and plotted the ratio B(r)/B(5cm) of the B field at any radius to the one at 5cm, to eliminate this unknown. Also, the plot only shows the absolute value as some students submitted negative changes.

I am quite satisfied with the results and am looking forward to the lecture in which we can presented the collective data to the students.

100.000 installs!

Woohoo, we have reached 100.000 installs (combined, Android and iOS) in less than a year. This is so amazing, thanks to you all! Please help us spread the word about phyphox even further by sharing your favorite experiment, a tweet/post/youtube video or just a link to our site with friends and colleagues – on the web or face-to-face.

Thanks again, to all of you!

Version 1.0.7 (GPS, saving of experiment states, …)

While we are already working on the big stuff like zoomable graphs, we decided to release yet another minor update in-between with some interesting features.

Full Changelog

And again, the full changelog for those who want to know every little detail or those who don’t like videos…

Changes for both Android and iOS

  • Save or share and load experiment states including your recorded data – even across platforms.
  • GPS support.
  • Audio autocorrelation and spectrum show corresponding musical notes.
  • You can now pick between different number of samples in audio spectrum.
  • New experiments: Accelerometer and magnetometer spectrum.
  • Time period of audio scope is now selectable.
  • Improved algorithm for audio autocorrelation.
  • Audio amplitude can now be calibrated to give sound pressure level in dB.
  • Splash screen with university logo.
  • Show magnetometer accuracy.
  • Move clear function to the action bar as a button.
  • Minor improvements to TalkBack / VoiceOver by adding descriptions to unlabeled buttons.
  • Buffer for acoustic stopwatch and inelastic collision has been increased, which might help on slower phones.

Changes for Android

  • Fix crash on Android 7.1 and Android O when reading non-3D sensors (like pressure or light).
  • Fix crash when rotating while the description hint starts showing.
  • Fix crash on bad experiment icons in main menu.

Changes for iOS

  • Fix crash on consecutive Fourier transforms.
  • Code has been converted to Swift 3. Ideally, there should be no noticable change. Ideally.
  • Old, discontinued audio engine has been replaced.
  • Fix: VoiceOver stopped working when phyphox handled audio.
  • University logo added to credits dialog.

File format update to version 1.5

  • Allow initializing buffers using a list of values.
  • Add mapping of ranges to value element to show text instead of numbers.
  • Add accuracy channel to sensors (magnetometer only).
  • Allow for dynamic sleep times of analysis cycles.
  • New analysis modules: round and log.
  • Fix handling of start value in subrange module.
  • Fix on Android: FFT module now uses actual number of data points instead of just the buffer size.
  • Fix on iOS: Button elements could not use buffers as inputs.

The editor and Wiki entries will be updated over the next few hours.

Hysteresis curve of an iron core

Christoph Holz from the University of M√ľnster has just added a fascinating new experiment to our Wiki: Hysteresis curve of an iron core.

He has created a phyphox experiment file which allows you to measure a hysteresis curve of a coil with an iron core using your phone’s magnetometer. In order to measure it as a function of the current through the coil he uses a simple method that could certainly be applied to other experiments as well – He simply uses a second coil without an iron core, which produces a magnetic field on another axis of the magnetometer, which is proportional to the current.

This is the first extensive contribution to our Wiki and this is exactly how the Wiki is meant to be used. If you have an experiment you would like to share, simply create a user account and start adding your article/experiment/note to the Wiki. Even if it is just a small contribution, we will welcome it glady.

phyphox visits the USA

There will be a short contributed phyphox talk and a poster at the AAPT Summer Meeting in Cincinnati from July 22nd till July 26th. If you want to meet me and discuss smartphone physics, I will be happy to meet you at a convenient time at the meeting (the poster session might be a little short and busy) – just send me an email (kuhlen@physik.rwth-aachen.de).

Tracking the speed of a wheel


We have just published an article in the German journal “Physik in unserer Zeit”, presenting phyphox and discussing its abilities to create customized experiments and remote control. We demonstrate this using a wheel rolling down a hill with the smartphone placed in its rim. In this experiment, phyphox autonomously determines the radius of the wheel and its velocity (similar to the roll experiment shipped with phyphox).

Physik in unserer Zeit 48, 148-149 (2017) (article in German)

If you want to try the experiment described in the article, you can open it directly in phyphox or download it. The experiment expects the phone to be as close to the outer radius of the wheel as possible and rotate about the x axis.