Question

A proton, an electron, a neutron, an `alpha`-particle and an unknown particle enter a region of magnetic field with equal momental. Figure shows paths (market 1 to 5) followed by these particles. Identify which path corresponds to which particle

Answer 1

The particle going straight (path3) must be a neutron. You can check from `vec(F) = q (vec(v) xx vec(B))` that particles deviating upwards are negatively charged and particles deviating down are positively charged. Now, `r = (p)/(qB) rArr r prop (1)/(q)`, as momentum is same for each particle
`rArr` Path 4 and 5 correspond to proton and `alpha`-particle respectively. Also 2 corresponds to electron as 4 corresponds to proton. (Why?)
`rArr` Unknown particles is negatively charged (obviously with charge more than that on electron), so if follows path of smaller radius
`rArr` Path 1 and path 2 correspond to unknown particle and electron respectively