A beam of alpha particles ( q = +2e, mass = 6.64 x 10-27 kg) is accelerated from rest through a potential difference of 1.8 kV. The beam is then entered into a region between two parallel metal plates with potential difference 120 V and a separation 8 mm, perpendicular to the direction of the field. What magnitude of magnetic field is needed so that the alpha particles emerge undeflected from between the plates?

The magnetic field required required for the beam not to be deflected  is

Explanation:

From the question we are told that

    The charge on the particle is

    The mass of the particle is  

    The potential difference is

    The potential difference between the two parallel plate is  

    The separation between the plate is  

The Kinetic energy experienced by the beam before entering the region of the parallel plate is equivalent to the potential energy of the beam  after the region having a potential difference of 1.8kV

Generelly

And      

 Equating this two formulas

making v the subject

Substituting value  

Generally the electric field between the plates is mathematically represented as

Substituting value  

the magnetic field  is mathematically evaluate