A non-relativistic proton beam passes without deviation through a region of space where there are uniform transverse mutually perpendicular electric and magnetic fields with `E= 120 kVm^-1 and B=50 mT.` Then the beam strikes a grounded target. Find the force which the beam acts on the target if the beam current is equal to `i=0.8 mA`.
Mass of protons `= 1.67xx10^(-27) kg`.

Answer

A, B

Explanation

`F_e=F_m` or `eE=eBv`
`:. V=E/B=(120xx10^3)/(50xx10^-3)`
`=2.4xx10^6m//s`
Let `n` be the number of protons striking per second.
Then,
`"ne"=0.8xx10^-3`
or `n=(0.8xx10^-3)/(1.6xx10^-19)`
`=5xx10^15m//s`
Force imparted`=`Rate of change of momentum
`=nmv`
`5xx10^15xx1.67xx10^-27xx2.4xx10^6`
`=2.0xx10^-5N`