Question

What is the electrical charge on the plate that causes the beam to bend toward the plate

Answer 1

The beam was attracted to a positively charged plate and repelled by a negatively charged plate.  The particles have a positive charge.   The plates caused the beam to deflect (bend) from its straight path since it was attracted by the positively charged plate.

Answer 2

Answer:

The electrical charge on the plate is positive.

Explanation:

The beam is a combination of cascading electrons. Since electrons are negatively charged, then the beam is negatively charged. Thus, it could either be attracted or repelled when in the neighborhood of a positive or negative charge. The law of electrostatic states that; like charge repels while unlike charge attracts. Thus, the beam was attracted to the plate because the former was positively charged. The plates caused the deflection of the beam from its initial path because it was attracted by the opposite charged plate.

Therefore, the beam was negatively charged while the plate was positively charged.