# How to apply Faraday's Law of Induction

1. Oct 13, 2011

### HyTronix

Greetings,

I have read the explanation on this forum here: https://www.physicsforums.com/showthread.php?t=441637 which discusses Faraday's Law of Induction, but I'm having a hard time understanding how to extrapolate that to my problem.

My goal:

Construct a circuit that measures ambient magnetic field strength, i.e., for finding wires, or determining if the ambient field strength is above a recommended (and likely arbitrary) background level of .5 Gauss.

I have a great deal of electronics experience, but, frankly, I'm terrible with math. Construction of the circuit is quite simple (I have a working spice model at any rate) but where Faraday's Law enters the picture is this:

-Assume the "probe" I've placed in this device is a 1mH inductor
-I'm expecting this probe to produce a voltage I can measure, likely in micro or millivolts

So, can anyone give me a working example that would help me understand this? For instance, if my 1mH inductor was placed into a field of .5G strength coming from a 60Hz power line, what voltage would be induced on the probe?

Thanks,

-John

2. Oct 13, 2011

### Bassalisk

Google for Hall Effect. That effect is essence for measuring ambient magnetic fields, Concept is quite simple. Although that is for DC currents, I think it should apply somehow to AC.

3. Oct 13, 2011

### jim hardy

aha magnetics is not well taught IMHO. n * dphi/dt is fine but what are the units?

i used ten turns on 14 inch diameter to give 0.1 square meter coil
so the voltage induced was direct indication of omega * (d phi/dt), flux in webers/m^2 which is 10,000 gauss.. at 60 hz w is 377 so next time i might make the coil 1/3.77 square meters.

i hope i have units right...

if your 1mh inductor is air core it might work but i wouldn't trust an iron core for fear it'll concentrate flux.

you need this book