InterviewSolution
Saved Bookmarks
InterviewSolution
| 1. |
A magnetic field set up using Helmholtz coils (described in Question 16 above) is uniform in a small region and has a magnitude of `0*75T`. In the same region, a uniform electrostatic field is maintained in a direction normal to the common axis of the coils. A narrow beam of (single species) charged particles all accelerated through `15kV` enters this region in a direction perpendicular to both the axis of the coils and the electrostatic field. If the beam remains undeflected when the electrostatic field is `9xx10^5Vm^-1`, make a simple guess so to what the beam contains. Why is the answer not unique? |
|
Answer» Here, `B=0*75T`, `E=9xx10^5Vm^-1`, `V=15kV=15000V, e//m=?` Let e be the charge and m be the mass of the particles. Let v be the velocity acquired by the particles, when accelerated under an accelerating voltage V, then `1/2mv^2=eV` Since the particles are not deflected by the two crossed fields, so `eE=evB` or `v=E//B` `:. 1/2m(E^2)/(B^2)=eV` or `e/m=(E^2)/(2VB^2)=((9*0xx10^5)^2)/(2xx15000xx(0*75)^2)=4*8xx10^7C//kg` This value of `e//m(=4*8xx10^7C//kg)` corresponds to deutrons, hence particles are deutrons ions. But the above value of `e//m` is also for `He^(++)` and `Li^(+++)`. [As `e//m=2 e//2m=3 e//3m]`, so the particles can be `He^(+++)` or `Li^(+++)` also. |
|