• Otávio Santiago

The Physics of the N95 Face Mask

IT’S 2022, AND by now we’ve all been wearing masks for nearly two years. And unless you are a surgeon or a construction worker who was already wearing them daily, in those two years you’ve probably learned a lot about them—which ones you like best, where to get them, and whether you have any extras stashed in a coat pocket or somewhere in your car.

But do you know what makes the prized N95 mask so special? Let’s find out.

Electric Charges

The fibers in regular cloth or paper face masks filter out particles by physically blocking them—but the fibers in an N95 mask also use a great physics trick. These fibers are electrically charged.

Electric charge is one of the fundamental properties of all particles. Just about everything around you is made of three particles: the proton, the electron and the neutron. (For now, let's ignore muons and neutrinos—both fundamental particles that actually exist—as well as other particles that are theoretically possible.)

Just as every particle has a mass, it also has a charge. The proton has a positive electric charge with a value of 1.6 x 10-19 coulombs, the unit for measuring electric charge. The electron has the exact opposite charge. That leaves the neutron with zero charge (thus the "neut" part of “neutron”).

The electric charge is a key part of the electrostatic interaction, the force between electric charges. The magnitude of this force depends on the magnitudes of the two charges and the distance between them. We can calculate this force with Coulomb's law. It looks like this:

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