Question

A free electron is placed in the path of a plane emw.The electron will start moving

Answer 1

If a electron is placed in the path of a electromagnetic plane then the electron will start moving along the electric field

Answer 2

An electron in an electromagnetic field, will follow a circular or helical path, according to the angle between the electric and magnetic fields. The electric field provides it the displacement and magnetic field, the direction. In case both the fields are perpendicular, the election will follow a circular path. In other cases it deep depends on each field's magnitude.