Question

write the condition under which an electron will move undeflected in the presence of crossed electric and magnetic fields?also explain your answer

Answer 1

The electron will move undeflected in the presence of crossed electric and magnetic field if the electric force on the electron is balanced by the magnetic force acting on the electron ,
Mathematically q E = q V B
Where q - charge
E - electric field
B - magnetic field
V - velocity of the electron
In the given problem q = v (charge on electron )
e E = eVB

Answer 2

Hey !!

Crossed electric and magnetic fields is that when electric and magnetic fields are perpendicular to each other, so under such circumstances, electrons will move undeflected due to electric force on electron which gets balanced by magnetic force acting on it.

     Hence, qE = qvB

where, q = charge , E = electric field , B = magnetic field , v = velocity of the electron

As, q = v show charge on electron, so eE = evB then v = E/B

GOOD LUCK !!