A stream of electron and protons are directed towards a narrow slit in a screen the intervening region has a uniform electric field E vertically downwards and a unifrom magnetic field B out of the plane of the as shown then

Options

A. electrons and protons with speed `|(vec(E ))/(vec(B))|` will pass through the slit
B. protons with speed `|(vec(E ))/(vec(B))|` will pass through the slite, electrons of the same speed will not
C. neither electrons nor protons will go through the slit irrespective of their speed.
D. electrons will always be deflected upwards irrespective of their speed.

Answer

C, D

Explanation

A charge q moving with velocity `vec(v)` in presence of both electric field `vec€` and magnetic field `vec(B)` experiences a Loreniz force and is given by
`vec(F)= q (vec(E )+ vec(v) xx vec(B))= vec(F)_(E )+ vec(F)_(B)`
If the total force `vec(F)` on the charge is zero, the charge will move in the fields undeflected.