What do you understand by magnetic field ? What is the force acting on a moving charge in a uniform magnetic field ? Discuss the cases when the force is maximum and minimum.

Explanation

Magnetic : Field : It is space around a magnet or a current-carrying conductor, in which its magnetic influence can be experienced. It is represented by `vecB.`
Expression for the force acing on moving charge placed in a magnetic field `vecB:`
Consider a positive charge .q. moving in a uniform magnetic field `vecB` with velocity `vecv.` Let hte angle between `vec v and vec B.` be ` theta.` The moving charge experiences a force F which depends upon the following factors :

(i) The force F is directly proportional to charge q i.e., `F prop q.`
(ii) F is directly proportional to component of velocity perpendicular to `vecB` i.e., v sin `theta `
`therefore F prop r sin theta.`
(iii) F is directly proportional applied magnetic field `vecB i.e., F prop B` Combinating all these factors,
we get ` F prop q v sin theta B : or F = k q v B sin theta `
where k is constant of proportionality and its value is found to be l.
`implies F = q v B sin theta " "...(i)`
or in vector form `vecF = q ( vec v xx vecb)" "...(ii)`