Paradox

A little something I thought up when I was 17. I'd assumed it would be much more challenging and expensive to make than it would actually be in reality so I never tried. I'd been thinking it would involve an extremely long iron bar, not knowing that microwave frequency oscillators exist. Unfortunately I currently have neither the money nor the free time to build this, but would have definitely done so in the past had I known how easily it could have been done.
The reason this is interesting is: the laws of physics contradict each other regarding what will actually happen if such a device is actually switched on!
I don't know which law will be disproven but I have a hunch it will be the first law of thermodynamics.