A long, straight wire of radius r carries a current i and is placed horizontally in a uniform magnetic field B pointing vertically upward. The current is uniformly distributed over its cross section. (a) At what points will the resultantant magnetic field have maximum magnitude? What will be the maximum magnitude? (b) What will be the minimum magnitude of the resultant magnetic field?

Explanation

The magnetic field will be maximum at point P whare net magnetic field `= B + (mu_0i)/(2pir)`
`. (b) magnetic field B = 0 when `rlt(mu_0i)/(2piB)`
`. But when `rgt(mu_0i)/(2piB)`
`. Net magnetic field = B - (mu_0i)/(2pr)`.