Hysteresis curve of an iron core

Christoph Holz from the University of Münster 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 (

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.

Walnut attack

This is a somewhat more unusual experiment: A little more than a week ago, the SPQR group of the University of Michigan has demonstrated, that it is possible to manipulate the readings of an accelerometer with sounds at the sensor’s resonance frequency (Original source). They called this the walnut attack and you can reproduce this with phyphox.

The phyphox version of this experiment generates a sine tone from the speaker and slowly sweeps it from 200 Hz to 20000 Hz while monitoring the data from the accelerometer. You can place your phone on a stable surface, start the experiment and wait for the result. If your accelerometer is susceptible to this type of manipulation, you will see resonances, like in this example from an iPhone 6s.

You can clearly see how the readings from the accelerometer deviate at certain frequencies although the phone is resting.

If your phone is not susceptible, you should barely see any deviations at all like in this example of an Nexus 5X.

If you want to try it yourself, just open the following link on a smartphone with phyphox. (If you came here without knowing about phyphox: It’s a free app for doing physics experiments with your phone, just go to the start page to learn about it.)
Walnut-Resonance experiment

By the way: Don’t worry if your phone shows a resonance. So far, the worst attack based on this is manipulating the number of steps counted by your fitness-tracker…

Workshop in Erfurt

Just finished the first of two workshops for teachers in Erfurt with great feedback. Looking forward to the second session. For our participants (and anyone else who is interested), here are the info sheets for each of the experiments presented in the workshop (the workshop is in German, so these are in German too): PDF