electricity and magnetism(2)

(a) Negative charge.

(b) Since mv^2/r = qvB

where r is the radius of the curved path at any instant
v is the speed of the particle
B is the magnetic flux density
m is the particle mass
q is the particle charge
hence, v/r = qB/m
i.e. v = (qB/m).r
v is proportional to r as the term (qB/m) is a constant.

Because the radius of the curved path gradually increases, thus the speed of the particle also increases.

(c) Becuae the particle is -ve charged and its speed gradually increases after release from the centre, the metal cylinder is thus at a potential higher than that at the centre.