For my final Physics 397 lab I’m working with Andrew Burke and Steve Jim, we’re studying propulsion. The idea is that we ionize air in the presence of a strong electric field, accelerate the electrons in one direction and the cations in the other direction. As a result in the mass difference (more than 10000:1 for atmospheric gasses) There is thrust generated according to Newton’s third law.

The magnitude of the propulsion force depends on how much air is being ionized and the electric field that it is going to be accelerated across (remember that the mean free path in air (SATP) is on the order of microns, not meters). Generating an electric field strong enough to strip electrons from air molecules isn’t all that simple when you imagine how strong it needs to be, but there is a relatively simply way of doing it. A very simple application of Gauss’s Law to an infinite line charge shows that the field goes like (lambda)/(2*pi*eo*r) where lambda is the linear charge density eo is the permittivity of free space, and r is the distance from the axis of the line charge. That means that the electric field gets arbitrarily large as you approach a theoretical line charge.

To charge a very thin wire (good approx of line charge) we just need to include it in a capacitor and put a large voltage across it. We’re just suspending the thin wire (42 gauge magnet wire) above a large radius of curvature conductor (piece of Al foil).

To measure the force generated (as the obvious manifestation of the phenomenon) we’re suspending the apparatus on a pendulum and measuring the angle of deflection from vertical.

Prelimiary tests have shown that we’re not completely out to lunch, we’re deflecting our “flyer” by close to 100 with a mass of many tens of grams if not hundred (haven’t yet measured).

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