The magnetic field is confirmed in a square region. A positive charged particle of charge q and mass m the limiting velocities of the particles so that it may come out of face (1), (2), (3), and (4).

Explanation

For the positive charge coming out from face `(1)`, the radius of the path in magnetic field should be less than or equal to `l//4` . For limiting case

`r_(max)=(l)/(4)=(mv)/(qB)impliesv_(max)=(qBl)/(4m).` Hence, if the velocity is `lt(qBl)/(4m)`, the charge particle comes out of face `(1)`. We can observe from right palm rule that the particle cannot come out from face `(1)`. For a positive charge coming out of face `(4)` let particle come out at point `N` from `DeltaOMN`
`(ON)^(2)=(OM)^(2)+(MN)^(2)`,
`r^(2)=(r-(1)/(2))^(2)+t^(2)impliesr=(5)/(4)l`.If the particle comes out from face `(4),rlt(5)/(4)implies(mv)/(qB)lt(5)/(4)l(or)vlt(5)/(4)(qBl)/(m)`. If velocity `vgt(5)/(4)(qBl)/(m)`, the particle will come out from face 3.