10 pointsl Zero Deflection A particle with charge +q and velocity W enters the region between...

here,

the upper plate of the capacitor is connected to positive plate so it is positively charged

so, the direction of electric field lines is downwards

so, the direction of electric force must be in downward direction for positive charge

for the particle to pass undeflected , the net force must be zero

to cancel out the electrostatic force , magnetic force must be in upward direction

and velocity is to the right

using right hand rule

the direction of magnetic field is INTO THE PAGE

and

as the net force must be zero

q * u * B = q * E

B = E /u

B = ( dV /d) /u

B = (dV)/(d * u)