Hello!
We can use the following equation for magnetic force on a charged particle:
![F_B = qv \times B](https://tex.z-dn.net/?f=F_B%20%3D%20qv%20%5Ctimes%20B)
= Magnetic force (N)
q = Charge of particle (1.6 × 10⁻¹⁹ C)
v = velocity of particle (5.2 × 10⁷ m/s)
B = Magnetic field strength (1.4 T)
This is a cross-product, so the equation can be rewritten to F = qvBsinφ where φ is the angle between the magnetic field and particle velocity vectors.
Since the proton's velocity vector and the magnetic field vector are perpendicular, sin(90) = 1. We can reduce the equation to:
![F_B = qvB](https://tex.z-dn.net/?f=F_B%20%3D%20qvB)
Plug in the known values.
![F_B = (1.6*10^{-19})(5.2*10^7)(1.4) = \boxed{1.1648 *10^{-11} N}](https://tex.z-dn.net/?f=F_B%20%3D%20%281.6%2A10%5E%7B-19%7D%29%285.2%2A10%5E7%29%281.4%29%20%3D%20%5Cboxed%7B1.1648%20%2A10%5E%7B-11%7D%20N%7D)
Gas, because it's particles are not very close to each other when compared to the other two.