# Would electromagnetic radiation impart a pressure on a surface of neutrons?

In my physics textbook, it says that a qualitative way to envision pressure from EM waves is as follows: the electric field drives charges in the $x$ direction, and the magnetic field then exerts on them a force $q\vec{v}\times\vec{B}$ in the $z$ direction. The net force on all the charges in the surface produces the pressure.

But if this is the case, then does that mean that EM waves wouldn't impart any pressure on a surface of neutrons, given there are no charges to move?

Let me know if this is just an analogy that doesn't hold... but in this case, is there another intuitive way to understand why there's a pressure associated with the waves? I understand mathematically, but not physically.

In my physics textbook, it says that a qualitative way to envision pressure from EM waves is as follows: the electric field drives charges in the x direction, and the magnetic field then exerts on them a force qv⃗ ×B⃗ in the z direction. The net force on all the charges in the surface produces the pressure.

This is a bit inaccurate, the pressure is not produced but shown off, exhibited, because light has a momentum that impacts the surface atoms, in the manner shown in the paragraph, and this momentum is transferred as pressure to the material : pressure is force per unit area, and dp/dt is force in incremental form.

It is intuitively simpler to think of light as innumerable photons, i.e. light particles. Then it is like a cloud of balls impacting a surface and transferring their momentum.

But if this is the case, then does that mean that EM waves wouldn't impart any pressure on a surface of neutrons, given there are no charges to move?

There is no matter composed only of neutrons except some in neutron stars. Neutrons are tied in with protons in creating the atoms which build up the molecules and the surfaces described in the paragraph in your book. There always is a spill over electric field about atoms.

Now for the sake of argument, let us suppose we had a bit of a neutron star with only neutrons and we threw a beam of light at them. Would the light pass through?

Again thinking in term of photons, i.e. individual interactions , tells us that the photons will be scattering on the neutrons because the neutrons have a magnetic moment (spin) and therefore a magnetic field and the photons will interact with that. It will be a smaller interaction than an interaction on atoms, called higher order, and light would penetrate further, but still finally the momentum would be transferred and a pressure will be evident from the wave.