Hello,

Has anyone put a phyphox-phone in a light-tight box together with a 10F Capacitor charging/discharging connected to ta lightbulb watching the light-sensor's output?

Well, you don't have to put the capacitor in the box, just the light bulb and the phone of course.

I wonder if you'd get a nice smooth exponential curve, and whether you could use the data to determine R*C?

Best regards.

//Erik

The light intensity from any light bulb is not a linear function of the electric tension... but you can try. I wonder if it gives an exponential with a modified decay time. You can use the acoustic entry to make this experiment but where take a square wave generator? Also using the sound card?

(11-26-2021, 08:49 AM)solid Wrote: [ -> ]The light intensity from any light bulb is not a linear function of the electric tension... but you can try. I wonder if it gives an exponential with a modified decay time. You can use the acoustic entry to make this experiment but where take a square wave generator? Also using the sound card?

What about the rotation of a small electrical motor? Would that be linear?

Regardless, the first try with discharge over an purposely unbalanced motor shows a decreasing frequency that looks like it's exponential (which it should).

Best regards.

//Erik

The frequency history rather looks like a piecewise linear function…

Hm, rotation energy comes with frequency squared, so … it's complicated, isn't it?

Should be able to plot rotation frequency as a function of voltage at some point, just now I wanted to find a way to show students that what they see (i.e. that the motor runs on the charged capacitor until it stops) can be visualised with a graph that looks similar to the graphs in their books.

So it just has to look like an exponential decay.

What was quite interesting is that the frequency measurement probably picked up different harmonics of the vibration. I was holding phone and everything in my hands, so I probably damped the vibrations differently while "measuring".

Didn't try the light sensor idea yet since the 5 "lab-phones" I have don't have light sensors (SM-J500FN).

Light sensor setup worked really well with a quite old phone (GT-i9300)!

No black box needed.

It's a 10 F capacitor and a 3.5 V 0.5 A lightbulb.

Could be worth while to pin down the lightbulb's illuminance v. voltage dependence.

Best regards.

//Erik

Thanks for the update. Do you have exported the data and checked if an exponential fit is sort-of ok?

(12-15-2021, 09:02 PM)Jens Noritzsch Wrote: [ -> ]Thanks for the update. Do you have exported the data and checked if an exponential fit is sort-of ok?

Not yet, I have very little "free" time. I'm not sure I am overlooking something here, but it seems to me this could be a two step experiment (using the same simple setup) where students first determine the illuminance voltage dependence and in the second step determine whether the discharge is exponential.

Thanks for feedback!!

Best regards.

//Erik