Final answer:
Beta particles will be deflected upward when they pass between two charged plates, with a positive charge at the top and a negative charge at the bottom, due to their negative charge being attracted to the positive plate.
Therefore, the correct answer is: option a). be deflected upward
Step-by-step explanation:
According to the principles of electromagnetism, a charged particle will experience a force when it enters an electric field, which will cause it to accelerate in a direction dictated by its charge relative to the field.
When a beta particle beam is directed between two charged plates, with a positive charge on top and a negative one below, the beam will be deflected upward. This happens because beta particles are high-speed electrons with a negative charge.
In this case, the fields created by the positively charged upper plate and negatively charged lower plate will exert a force on the beta particles that pulls them towards the positive plate. Consequently, the beta particles will be deflected upward due to their negative charge, towards the positively charged plate.