A magnetic field B⃗ = B₀ ĵ exists in the region 𝑎

Question

A magnetic field B⃗ = B₀ ĵ exists in the region 𝑎< x< 2𝑎 and B⃗ = - B0ĵ, in the region 2a < x < 3a, where B₀ is a positive constant. A positive point charge moving with a velocity = v₀, where v₀ is a positive constant, enters the magnetic field at x = a. The trajectory of the charge in this region can be like,

G1 Physics · Accepted Answer

In the first strip B is +B₀ĵ and in the second it reverses to -B₀ĵ, so the magnetic curvature reverses sign at x=2a while speed remains unchanged. The only trajectory with the required continuous tangent and opposite curvature is Image 1, option A.